Case Study Demonstrates the Importance of Knowing the Root Cause of the Concern Before Designing

Photo 1. In order to manufacture materials inside the facility, humidity had to be added to the space in the form of hanging moisture dispensaries. This increased the relative humidity to 90 percent with interior temperatures reaching 90 degrees. Images: Hutchinson Design Group Ltd.

The client said, “The roof leaks in the dead of winter.” Interesting when the exterior ambient temperature is below zero. The client’s firm had purchased the metal building several years earlier and water had come in every winter. A key piece of evidence was that the original building was used for storage. The new entity purchased the building for manufacturing. Not just manufacturing, but manufacturing of medical-grade textiles that require the use of humidity to reduce static electricity. Not just humidity, but 90 percent relative humidity (RH), where visible water is sprayed into the air. (See Photo 1.) Interior temperatures routinely reached 90 degrees. Now, let’s see: 90 degrees with 90 percent RH inside, zero degrees outside, and 6 inches of vinyl face batt insulation compressed at the purlins with aged, open lap seams. Not good. The mission, if I chose to accept it, was to eliminate the leaking on a roof that was watertight.

Proposed Solutions

During my first meeting with the client, I was provided with proposals from roofing contractors and, sad to say, several roof consultants. Proposed solutions ranged from coating the metal, to flute filler and cover board with a mechanically attached thermoplastic membrane, to flute filler, 2 inches of insulation and adhered thermoplastic. None of the proposals identified the interior’s relative humidity and heat as a concern, and thus these issues were not addressed. So, a good part of the morning was spent educating the client as to why none of the proposed solutions would work. Imagine spending big bucks on a roof solution that would have only exacerbated that situation.

Photo 2. Rising humidity passed breaches in the vinyl vapor barrier in the insulation and condensed on the underside of the metal roof panels. The water would then drip down on to the insulation, and eventually the vapor retarder seams would open and water would pour in.

The existing building was a metal building by Kirby (similar to a Butler Building if that helps). The roof was a trapezoidal seam metal roof panel 24 inches wide on a low slope to an offset ridge. The panel runs from ridge to eave were 200 feet to the north and 100 feet to the south. The roof drained to a gutter on the north and lower metal roof on the south. The east and west roof edges were standard metal building rake metal. The walls were vertical metal siding with exposed screws. The roof and metal wall panels were set over vinyl faced insulation draped over purlins. While there was exhausting of the interior air — typically used in the summer — and some provisions for adding exterior air in the winter and summer, there was no overall mechanical control of the interior.

The Key Issue

While a freezer building has extreme energy low trying with every ounce of its being to pull hot humid air in, this structure has extreme energy high trying to “get out.” The warm, humid air is seeking every crack, split in the insulation facer, and open lap seam to move toward equalization. This warm, humid air was making its way to the underside of the metal roof panels, condensing, and running down the underside of the panel until it dropped off.

Figure 1. Typical Roof System Section

After time, the accumulation of the water in the batt insulation created a large belly until the adjacent lap seam broke and large amounts of water came cascading down. Soiled product had to be discarded. With rolls 5 feet wide and a 6 feet diameter, the losses could be substantial. Water on the floor was also a safety issue. Additionally, when this damage occurred the insulation layer now had an opening which sucked in even more interior air; the condensation increased and water dripping to the floor was an even bigger problem. This was occurring in numerous conditions, with the greatest accumulation of water in the insulation near the ridge. (See Photo 2.)

Determining the Solution

Prior to delving into a potential solution, a parti, or overall concept of architectural design, had to be developed. In this case I decided that the metal roof would become the vapor retarder for the new roof. Simple enough. If the metal roof is to become the new vapor retarder, the key was to keep it warm enough so that even if it came in contact with the interior air, it would not result in condensation. We did this by determining the dew point for several insulation scenarios and found that with the batt insulation still in place and 90 percent RH with a temperature of 90 degrees inside, with an exterior design temperature of minus 10 degrees, 6 inches of insulation above the 2.5-inch flute filler was required.

Photo 3. For budget reasons, the liquid flashing seal of the trapezoidal seams was eliminated. As the metal roof had to act as the vapor retarder, a self-adhered membrane was installed first over the trapezoidal seam and fit into the articulated seam with “finger” rollers, and then placed over the center of the panels and fit around the panel striations.

All roof system designs need to be thought of holistically, as the success depends on the sum of all the components working together. So, let’s start with the roof panel and structural system. Designers of metal buildings are notorious for minimizing each and every structural member to lower costs. A structural check found that the existing structure was able to handle the weight of a new roof system. Prior to proceeding, a mechanical fastener pull-out test was performed by Pro-Fastening Systems of Buffalo Grove, Illinois, an Olympic Distributor (need a special or standard anchor, these guys have it). The tests showed that the 22-gauge metal panel was able to engage the buttress thread screw.

To be effective, a vapor retarder needs to be airtight — or for you purists, have extremely low or no permeability at all — and this metal roof had to function as a vapor retarder. The steel roof panel itself is impermeable, but the seams, though mechanically locked, have the potential under interior pressure to allow air to pass through. The seams had to be sealed. The mechanical fasteners penetrating the metal roof panel needed to be sealed as well. The roof transitions at the vertical rake walls, gutter and low roof also needed to be sealed. After looking at the standing seams, it was decided that they could not be assumed to be airtight, so we selected to seal them with a liquid flashing. As the mechanical fasteners would penetrate the panel, a bituminous self-adhering and hopefully self-sealing vapor retarder was placed on the panel. (See Figure 1 and Photo 3.) Transverse laps, removing the ridge cap and infilling the opening were all addressed. The rakes presented unique challenges which took some good thinking on how to seal. Ultimately, it was decided that a combination of removing the rake metal and installing a prefabricated roof curb and membrane vapor retarder would do the trick. (See Figure 2.)

Figure 2. Rake Edge Detail

My initial thought was to begin the thermal layer with a layer of expanded polystyrene (EPS) on the deck designed to fit the trapezoidal seam profile. This left a void at the seams, so the void between the seam and EPS was sealed with spray foam insulation. (See Photo 4.) The insulation was then mechanically fastened. The thickness of the EPS was 3/8 of an inch greater in height than the standing seam to compensate for varying seam heights. Over the EPS, one layer of 2.6-inch fiberglass-coated faced, 25 psi polyisocyanurate insulation was designed to be mechanically fastened to the roof panel. The top layer of insulation was a 2.6-inch fiberglass-coated faced, 25 psi polyisocyanurate insulation, which was designed to be set in full spatter cover flexible polyurethane foam adhesive. A cover board with the receiver facer to which the membrane would be attached was designed to be set in a full coverage of splatter applied polyurethane insulation. (See Photo 5.)

Photo 4. The EPS was cut to fit the panel profile. The joint at the seam was sealed with spray foam insulation.

As the installation was to take place in late fall and during the winter, adhesive use was determined to be challenging if not impossible, so the roof cover selected was a 90-mil Carlisle FleeceBACK black EPDM. The fleece on the membrane would engage with a unique hook and loop facer and reduced by 95 percent the amount of adhesive required. (See Photo 6.) Six-inch seam taped end lap seams with self-adhering cover strips were designed, while the butt seams were also double sealed with 6-inch and 12-inch cover strips.

The rake edge was designed to be sealed at the top of the metal panels and raised with an insulated metal curb. (See Photos 7 and 8.) The wall panels’ reverse batten seams and bowed inward panel were designed to be sealed with a foam closure set in sealant. The architectural sheet metal on the rakes was a four-piece system of fascia and coping. The roof edge gutter was enlarged and reinforced to hold up to solid ice.

Construction

Photo 5. Once the EPS “flute filler” was in place, two layers of 2.6-inch coated fiberglass insulation were mechanically fastened into the standing seam panels. The high-density cover board was then installed in spray foam adhesive.

The project was bid out and AR Commercial of Aurora, Illinois, was selected. Work on the project began in October 2018 and was completed in April 2019. (See Photo 9.) Like any project, various miscellaneous items not anticipated arose, such as extreme cold early in the fall that precipitated the decision to mechanically attach the insulation in lieu of cold adhesive application. I also forgot about the residual water in the existing batt insulation. While we designed for 90 percent RH and temperatures of 90 degrees, we didn’t anticipate the 100 percent RH condition where the soaked batt insulation was located, which resulted in condensation occurring during the deep freeze. You’re never too old to learn something new. The batts were cut open, dried and all is good.

Sometimes you need a good roof over your head to keep you dry, even when it doesn’t rain.

Photo 6. The FleeceBACK 90-mil EPDM sheets were aligned, rolled out, broomed in and rolled.
Photo 7. Following the removal of the existing rake metal, the roof vapor retarder was extended down and over the existing construction and onto the metal roof panel. The contractor came up with an innovative two-piece roof edge curb that allowed for ease of installation.
Photo 8. Following the installation of the interior curb side, which was accomplished with a jig for continuous alignment, the curb was insulated and the exterior cap piece installed.
Photo 9. The finished roof prevented condensation from occurring even when the ambient temperature dropped to minus 28 degrees with wind chills near minus 50 degrees.

About the author: Thomas W. Hutchinson, AIA, FRCI, RRC, CRP, CSI, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information, visit www.hutchinsondesigngroup.com.

The 7 Commandments of Roofing

If I were the Roofing God for a day, what would I change? Oh, where do I start? First of all, there would be none of this “you should,” “can,” “may” or “it is recommended” nomenclature. I would have commands: Thou shall do the following.

Freezer Buildings and Block Ice Insulation

Photos 1 and 2. When moist exterior air is pulled into the roof systems of freezer buildings, the moisture condenses and freezes. Here gaps in the insulation are filled with ice. On the interior there are icicles more than 10 feet long. The cause? Air intrusion at the roof edge under the membrane and wood blocking. Images: Hutchinson Design Group Ltd.

I have never opened up a roof over a freezer building that wasn’t solid ice between the insulation joints. How does this travesty occur? Ignorance? In part. Naiveté? Yes. Who is guilty? Whoever is the roof system designer. Most designers should know that there is an enormous moisture drive from the exterior to the interior. This drive is not a passive movement, but a huge, sucking pressure. It’s like there is a shop vac in the interior trying to pull in outside air. But designers fail to realize that the first sources of interior moisture intrusion into the roof system are moisture migrating out from exposed soil until the concrete slab is poured; moisture coming from the interior concrete floor slab; and latent air moisture (relative humidity) in the interior air before the freezer is operational.

We in the roofing industry are very good at keeping water out of the building. It’s the influx of air that is destroying these roofs shortly after bringing the freezer online. So how is the air getting in? Oh, let me count the ways: (1) though the unsealed membrane at the roof edge; (2) past beveled precast concrete joints at the roof edge; (3) below perimeter wood blocking at the roof edge; and (4) up through metal wall panel joints.

Photo 2.

Stopping air transport to the interior is key. Most designers believe that the roof membrane performs as the air/vapor barrier. In the field of the roof, perhaps, but their lack of knowledge about roof material characteristics and proper installation methods often leads designers astray. The perimeter becomes the weak link.

Let’s look at some common design mistakes:

1. In recent years, designers have revised roof membrane selection to reflective roof membranes, in part to garner a LEED point. The trouble is that these membranes are substantially ridged/stiff and can be difficult to turn over the roof edge, adhere and seal, so they are often barely turned over the edge and nailed off. The lack of a positive seal (that would be achieved by adhering the membrane to the perimeter wood blocking and wall) allows air to move up below the membrane.

2. When precast concrete panels are used at the walls, the joints are often beveled. What happens at the roof edge? The bevel extends right up to the perimeter wood of the coping that is straight and parallel to the outside wall face. The bevel becomes a gutter to channel wind up the wall to the underside of the gutter, gravel stop or coping. In a situation like the one outlined in No. 1 above, the wind can move in below the roof system.

3. When perimeter wood blocking is placed in a horizontal position at the roof edge, the underside of the wood blocking needs to be sealed. A non-curing, gun-grade butyl, applied in several rows, works well, such that when the blocking is secured to the wall, the underside of the blocking is sealed. Be aware of uneven substrates that will require additional sealant.

4. Metal wall panel joints are another potential problem spot. Ask a metal wall panel installer why they are only sealing one of the two exterior male–female joints and you are likely to hear, “because the exterior joint completes the vapor retarder” (which is on the exterior of the building when perfect). Technically they are correct. However, getting a perfect sealant joint to create a complete vapor retarder is not so easy. Think of how sealant is applied. The installer squeezes the caulk gun handle and the sealant oozes out in a thick bead, which can vary in thickness as the gun is drawn along. As the trigger is squeezed and the gun moves, the sealant bead decreases in diameter, and then the gun handle is squeezed again and a thick bead oozes out, and so on. At the end of the sealant application, the thinned-out bead is often not sufficient to properly seal the panels where they are engaged. Condensing water weeps out of the joints in the interior in cold storage areas and results in interior ice on freezer buildings. The sealant, whether factory applied or field applied, is not located at the exterior plane of the panel, but recessed in the outer tongue and groove joint, leaving the potential (almost a guarantee) that there will be a vertical “chimney” of about 1/16 of an inch that can channel air up under the membrane turned over the wall panel.

A quality vapor retarder (those of you thinking polyethylene, think again) placed on the roof deck will protect the thermal layers from vapor intrusion from the interior humidity, latent construction moisture, and ground moisture that accumulates before freezer draws down. It also prevents exterior air infiltration, which can result in interior “snow” and the huge icicle formations. (See Photos 1 and 2.)

Commandment #1: Thou shall place a vapor barrier at the roof deck on freezer/cold storage buildings and seal roof edge perimeters, drains and penetrations through the vapor retarder and all perimeter conditions to be airtight.

The Roof Drain Conspiracy

I am convinced that there is an international conspiracy to drive me nuts. It’s called the ‘how small can we cut out the membrane at the roof drain’ contest. (See Photo 3.)

Photo 3. Believe it or not, this is not even close to the winner of “who can cut the smallest hole in the roof membrane at the drain” contest. The membrane should be cut back to within 1/2 inch of the clamping ring to allow the drain to function as designed.

When I am called in as an expert on a building collapse, the first thing I tell the attorney is, “Save the roof drains and attached roof membrane!” Why, you ask? Because I want to see if the roofing contractor competed in the contest and if the installer and the consultant/architect will be party to the repair costs. Drains are designed to create a vortex to drain water most efficiently from the roof. (Watch how a toilet flushes to gain an understanding on how a drain works with the water swirling into the drainpipe.) The shape of the water flow from the roof surface to the drain bowl to the downspout is critical. When the hole cut in the membrane is too small, it can restrict drainage. Costs often drive projects, and it is not uncommon for a roof’s structural elements to be value engineered down to the bone. With intense rainfalls (you know, the 100-year rains that are occurring two or three times per year) and on larger roof areas where large outlet pipes are used, restricted water drainage can and has resulted in structural roof collapse.

So, I’m on a roof and observe the roofing crew cutting out a small hole at the drain. Being the conscientious consultant that I am, I ask, “Can you please cut out the membrane to within 1/2-inch of the clamping ring?” The answer is almost universal: “I’ll do it later.” Usually my blood pressure rises and face turns red as I explain the importance of making sure this detail is not overlooked.

Our details call out the proper way to cut out the membrane and our field observation reports call this out to be corrected, but I am forced to remind contractors again and again — sometimes even when it’s on the punch list. So, what’s a consultant to do? I reject the pay request.

Commandment #2: Call out on your roof drain details to cut back the membrane to within 1/2-inch of the clamping ring (a cloverleaf pattern around the bolts is best), and drive home the importance of this detail to the crew members in the field.

The 12-Inch Roof Curb

Photo 4. Roof insulation thicknesses now required by code make 12-inch roof curbs obsolete. Specify 18-inch curbs. Raising this curb with 16-gauge steel was very expensive. I suggested sending the bill to the engineer.

When energy was cheap, insulation was an inch or two in thickness, and the roof was built up, 12-inch-high roof curbs worked. With the new insulation requirements and tapered insulation, 12-inch curbs can be buried. Furthermore, future code mandates may increase insulation R-value, increasing insulation heights. So, consider this a public announcement to all mechanical engineers and curb manufacturers: Eliminate 12-inch curbs and specify curbs that are 18 inches or higher. (See Photo 4.)

Commandment #3: Specify only 18-inch and above roof curbs and rails.

Flapping in the Breeze

Photos 5 and 6. The membrane left unsealed at the roof perimeter has placed this roof in great jeopardy of wind damage. It is also allowing water to flow back into the insulation.

Driving around Chicago it’s not hard to see roof edges — gutters, gravel stop, and parapets — where the roof membrane is just flapping in the wind. (See Photos 5 and 6.) This is especially a concern when the roof system is mechanically attached and the air can move directly below the membrane. The roof typically is installed prior to the installation of the windows and doors, and while the building is open, airflow in the interior can create upward pressure on the roof system from below. This force, in association with the air getting below the membrane at the roof edge and with uplift above the membrane, drastically raises the risk of wind damage. Furthermore, when the membrane is not secured at the gutter roof edge, water draining off the roof will return back to the roof edge and move into the building and insulation.

Photo 6.

Wrap the membrane over the roof edge, adhere it in place and nail it off. This will save you during the installation and prevent air infiltration once the roof is complete. The designer should also delineate the area where the air barrier meets the roof vapor retarder and/or roof membrane and define who is responsible for what. Detail this explicitly.

Commandment #4: Roof membranes shall be extended down over the edge wood blocking a minimum of 1.5 inches onto the wall substrate, fully adhered and nailed off on the day it is installed. Where applicable, seal to the wall air barriers.

Holding Roof Drains Off the Roof Deck

Photo 7. Drains held up off the deck make re-roofing difficult when a vapor retarder is called for. I have seen roofs covered with 1.5 inches of water due to high drains, with the water just waiting to relieve itself to the interior at the first vapor retarder deficiency.

Nothing is more frustrating to a roofing contractor during a re-roof than removing the old roof to install a vapor retarder and finding that the roof drain has been held up off the roof deck. (See Photo 7.) This goes back to the design when the engineer and architect have no clue as to the use of proper sump pans and roof drains with extension rings — preferably threaded.

Commandment #5: Design, detail and draw the roof drain detail showing the roof deck with a sump pan provided by the roof drain manufacturer, installed by the plumbing contractor not the guys installing the roof deck), with the roof drain now flush to the roof deck, with a reversible collar (to which the extension ring threads engage), the threaded extension ring and dome.

Fill the Void, Bury the Screw, Save the Energy

Photo 8. Often a roofing contractor will leave voids like this around penetrations. Imagine the energy loss.

With the push over the past decade for energy savings/conservation, it is amazing to me that the code bodies have ignored two very highly energy consumptive or energy loss conditions: (1) voids in the thermal layer at penetrations and perimeter conditions; and (2) mechanical fasteners with plates below the roof cover. (See Photos 8-10.)

Photo 9. This photo shows multiple problems, beginning with a stud wall and a large gap at the deck. Warm air coming up the wall will cause deterioration of the water-based adhesives on the base flashing. The insulation panels are not tight to the wall or to each other. The metal strip looks pretty thin, is not a proper vapor retarder termination and will not hold the screws of the base anchor. This is a project that will continue giving work to us expert witnesses.

Some crews work to fit insulation tight to conditions. Others don’t. Eyeballing the circular cutout at vent pipes is common, resulting in fairly large voids at vent pipes. Roof edge conditions vary and significant voids can occur there, too. All of these voids need to be sealed with spray foam insulation, which should be allowed to rise and then trimmed flush to the insulation. I recommend that the spray foam be installed at each layer as subsequent insulation layers can shift the void. We have been requiring this for years without much blowback from contractors. The only issue that arose was when a contractor wanted to use polyurethane adhesive to fill voids; that was a no-go, as the polyurethane adhesive collapses down after it rises.

Photo 10. The screws and plates seen here are costing the building owner a fortune in lost energy.

Mechanical fasteners used to positively secure the insulation and membrane have become commonplace. But as I’ve noted before, we have seen roofs covered in frost with hundreds, if not thousands, of little spots of melted frost. The heat transfer through the fasteners is substantial. Research has found that on a mechanically attached roof cover, the energy loss can be over 40 percent above that of a system without exposed fasteners. As energy requirements are defined by R-value and with the potential for thermal loss due to the fasteners, I propose an R-value penalty for exposed fasteners. For example, in Chicago where the R-value requirement is 30, if you have a mechanically attached roof cover, the R-value required would be 42. That way the thermal efficiency would be equivalent and building owners wouldn’t pay the price for the designer’s lack of knowledge. Thus, as the Roofing God, I would implement this penalty and require all adhered roofs to have fasteners buried below insulation or cover board layers.

Commandment # 6: Show and note on your details the installation of spray foam insulation at penetrations, roof drains and perimeters.

Commandment # 7: All mechanical fasteners should be covered with insulation or a cover board; if not, 40 percent more R-value needs to be added to the thermal layer to compensate for the energy loss.

So, there you have the new roofing commandments that I would bestow if I were the Roofing God for a day. Let’s all work together though to bring about positive change and increase the sustainability and resiliency of our roofs. Together we can do it.

About the author: Thomas W. Hutchinson, AIA, FRCI, RRC, CRP, CSI, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information, visit www.hutchinsondesigngroup.com.

Designing Thermally Efficient Roof Systems

Photo 1. Designing and installing thermal insulation in two layers with offset and staggered joints prevents vertical heat loss through the insulation butt joints. Images: Hutchinson Design Group Ltd.

“Energy efficiency,” “energy conservation,” and “reduction of energy use” are terms that are often used interchangeably, but do they mean the same thing? Let’s look at some definitions courtesy of Messrs. Merriam and Webster, along with my interpretation and comment:

· Energy efficiency: Preventing the wasteful use of a particular resource. (Funny thing, though — when you type in “energy efficiency” in search engines, you sometimes get the definition for “energy conservation.”

· Energy conservation: The total energy of an isolated system remains constant irrespective of whatever internal changes may take place, with energy disappearing in one form reappearing in another. (Think internal condensation due to air leaking, reducing thermal R-value of the system.)

· Reduction: The action of making a specific item (in this case energy use) smaller or less in amount. (Think cost savings.)

· Conservation: Prevention of the wasteful use of a resource.

So, looking at this article’s title, what does “designing a thermally efficient roof system” imply?

Photo 2. Rigid insulation is often cut short of penetrations, in this case the roof curb. To prevent heat loss around the perimeter of the curb, the void has been sprayed with spray polyurethane foam insulation. Open joints in the insulation have also been filled with spray foam insulation. Note too, the vapor retarder beyond the insulation.

I conducted an informal survey of architects, building managers, roof consultants and building owners in Chicago, and they revealed that the goals of a thermally efficient roof system include:

  • Ensuring energy efficiency, thus preventing the wasteful use of energy.
  • Reducing energy use, thus conserving a resource.
  • Being energy conservative so that outside forces do not reduce the energy-saving capabilities of the roof system.

Unfortunately, I would hazard a guess and say that most new roof systems being designed do not achieve energy conservation.

Why is this important? The past decade has seen the world building committee strive to ensure the energy efficiency of our built environment.

A building’s roof is often the most effective part of the envelope in conserving energy. The roof system, if designed properly, can mitigate energy loss or gain and allow the building’s mechanical systems to function properly for occupant comfort.

Photo 3. Rigid insulation is often not tight to perimeter walls or roof edges. Here the roofing crew is spraying polyurethane foam insulation into the void to seal it from air and heat transfer. Once the foam rises it will be trimmed flush with the surface of the insulation.

Energy conservation is increasingly being viewed as an important performance objective for governmental, educational, commercial and industrial construction. Interest in the conservation of energy is high and is being actively discussed at all levels of the building industry, including federal and local governments; bodies that govern codes and standards; and trade organizations.

As with many systems, it is the details that are the difference between success and failure on the roof. This article will be based on the author’s 35 years of roof system design and in-field empirical experience and will review key design elements in the detailing of energy-conserving roof systems. Best design and detail practices for roofing to achieve energy conservation will be delineated, in-field examples reviewed and details provided.  

Advocacy for Improvement

In the past decade, American codes and standard associations have increased the required thermal values every updating cycle. They have realized the importance of energy conservation and the value of an effective thermal layer at the roof plane. They have done this by prescribing thermal R-values by various climatic zones defined by the American Society of Heating and Air-Conditioning Engineers, now better known by its acronym ASHRAE. Additionally, two layers of insulation with offset joints are now prescribed in the IECC (International Energy Conservation Code). Furthermore, the American Institute of Architects (AIA) has also realized the importance of conserving energy and defined an energy conservation goal called the 2030 Challenge, in which they challenge architects, owners and builders to achieve “zero energy” consuming buildings by 2030.

These codes, standards and laudable goals have gone a long way to improving energy conservation, but they are short on the details that are needed to achieve the vision.

Energy Conservation Is More Than Insulation

Roofs are systems and act as a whole. Thus, a holistic view of the system needs to be undertaken to achieve a greater good. Roof system parameters such as the following need to be considered:

  • Air and/or vapor barriers and their transitions at walls, penetrations and various roof edges.
  • Multiple layers of insulation with offset joints.
  • Preventing open voids in the thermal layers at perimeters and penetrations.
  • Protection of the thermal layer from physical damage above and warm moist air from below.
Photo 4. The mechanical fasteners below the roof membrane used to secure the insulation conduct heat through them to the fastening plate. The resultant heat loss can be observed in heavy frost and snowfall.

Air intrusion into the roof system from the interior can have extremely detrimental consequences. In fact, Oak Ridge National Laboratory research has found that air leakage is the most important aspect in reducing energy consumption. Interior air is most often conditioned, and when it moves into a roof system, especially in the northern two-thirds of the country where the potential for condensation exists, the results can include wet insulation, deteriorating insulation facers, mold growth and rendering the roof system vulnerable to wind uplift. Preventing air intrusion into the roof system from the interior of the building needs to be considered in the design when energy efficiency is a goal. Thus, vapor retarders should be considered for many reasons, as they add quality and resiliency to the roof system (refer to my September/October 2014 Roofing article, “Vapor Retarders: You Must Prevent Air and Vapor Transport from a Building’s Interior into the Roof System”). The transition of the roof vapor/air barrier and the wall air barrier should be detailed and the contractors responsible for sealing and terminations noted on the details.

One layer of insulation results in joints that are often open or could open over time, allowing heat to move from the interior to the exterior — a thermal short. Energy high to energy low is a law of physics that can be severe. Thus, the International Code Council now prescribes two layers of insulation with offset joints. (See Photo 1.)

When rigid insulation is cut to conform around penetrations, roof edges and rooftop items, the cuts in the insulation are often rough. This results in voids, often from the top surface of the roof down to the roof deck. With the penetration at the roof deck also being rough, heat loss can be substantial. Thus, we specify and require that these gaps be filled with spray foam insulation. (See Photos 2 and 3.)

Insulation Material Characteristics and Energy Conservation

In addition to the system components’ influence on energy loss, the insulation material characteristics should also be considered. The main insulation type in the United States is polyisocyanurate. Specifiers need to know the various material characteristics in order to specify the correct material. Characteristics to consider are:

Photo 5. Heat loss through the single layer insulation and the mechanical fasteners was so great that it melted the snow, and when temperatures dropped to well below freezing, the melted snow froze. This is a great visual to understand the high loss of heat through mechanical fasteners.
  • Density: 18, 20, 22 or 25 psi; nominal or minimum.
  • Facer type: Fiber reinforced paper or coated fiberglass.
  • Dimensional stability: Will the material change with influences from moisture, heat or foot traffic.
  • Thermal R-value.

In Europe, a popular insulation is mineral wool, which is high in fire resistance, but as with polyisocyanurate, knowledge of physical characteristic is required:

  • Density: If you don’t specify the density of the insulation board, you get 18 psi nominal. Options include 18, 20 and 25 psi; the higher number is more dimensionally stable. We specify 25 psi minimum.
  • Protection required: Cover board or integral cover board.
  • Thermal R-value.

Protecting the Thermal Layer

It is not uncommon for unknowledgeable roof system designers or builders looking to reduce costs to omit or remove the cover board. The cover board, in addition to providing an enhanced surface for the roof cover adhesion, provides a protective layer on the top of the insulation, preventing physical damage to the insulation from construction activities, owner foot traffic and acts of God.

The underside of the thermal layers should be protected as well from the effects of interior building air infiltration. An effective air barrier or vapor retarder, in which all the penetrations, terminations, transitions and material laps are detailed and sealed, performs this feat. If a fire rating is required, the use of gypsum and gypsum-based boards on roof decks such as steel, wood, cementitious wood fiber can help achieve the rating required.

Insulation Attachment and Energy Efficiency

The method in which the insulation is attached to the roof deck can influence the energy-saving potential of the roof system in a major way. This fact is just not acknowledged, as I see some mechanically attached systems being described as energy efficient when they are far from it. Attaching the insulation with asphalt and/or full cover spray polyurethane adhesive can — when properly installed — provide a nearly monolithic thermal layer from roof deck to roof membrane as intended by the codes.

Figure 1. Roof details should be drawn large with all components delineated. Air and vapor retarders should be clearly shown and noted and any special instructions called out. Project-specific roof assembly details go a long way to moving toward ensuring energy conservation is achieved. Here the air and vapor retarder are highlighted and definitively delineated. Voids at perimeters are called out to be filled with spray foam and methods of attachment are noted.

Another very popular method of attaching insulation to the roof deck and each other is the use of bead polyurethane foam adhesive. The beads are typically applied at 6 inches (15.24 cm), 8 inches (20.32 cm), 9 inches (22.86 cm) or 12 inches (30.48 cm).

The insulation needs to be compressed into the beads and weighted to ensure the board does not rise up off the foam. Even when well compressed and installed, there will be a ±3/16-inch void between the compressed beads, as full compression of the adhesive is not possible. This void allows air transport, which can be very detrimental if the air is laden with moisture in cold regions. The linear void below the insulation also interrupts the vertical thermal insulation section.

The most detrimental method of insulation attachment in regard to energy loss is when the insulation is mechanically fastened with the fasteners below the roof cover. Thermal bridging takes place from the conditioned interior to the exterior along the steel fastener. This can readily be observed on roofs with heavy frost and light snowfall, as the metal stress plates below the roof cover transfer heat from the interior to the membrane, which in turn melts the frost or snow above. (See Photo 4.)

The thermal values of roofs are compromised even more when a mechanically attached roof cover is installed. The volume of mechanical fasteners increases, as does the heat loss, which is not insignificant. Singh, Gulati, Srinivasan, and Bhandari in their study “Three-Dimensional Heat Transfer Analysis of Metal Fasteners in Roofing Assemblies”found an effective drop in thermal value of up to 48 percent when mechanical fasteners are used to attach roof covers. (See Photo 5). This research would suggest that for these types of roof systems, in order to meet the code-required effective thermal R-value, the designer needs to increase the required thermal R-value by 50 percent.

Recommendations to Increase Energy Savings

Code and standard bodies as well as governments around the world all agree that energy conservation is a laudable goal. Energy loss through the roof can be substantial, and an obvious location to focus on to prevent energy loss and thus create energy savings. The thermal layer works 24 hours a day, 7 days a week, 52 weeks a year. Compromises in the thermal layer will affect the performance of the insulation and decrease energy savings for years to come. Attention to installation methods and detailing transitions at roof edges, penetrations, walls and drains needs to be given in order to optimize the energy conservation potential of the roof system.

Based on empirical field observation of roof installations and forensic investigations, the following recommendations are made to increase the energy-saving potential of roof systems.

  • Vapor and air barriers are often required or beneficial and should be specifically detailed at laps, penetrations, terminations and transitions to wall air barriers. (See Figure 1.) Call out on the drawings the contractor responsible for material termination so that this is clearly understood.
  • The thermal layer (consisting of multiple layers of insulation) needs to be continuous without breaks or voids. Seal all voids at penetrations and perimeters with closed cell polyurethane sealant.
  • Design insulation layers to be a minimum of two with offset joints.
  • Select quality insulation materials. For polyisocyanurate, that would mean coated fiberglass facers. For mineral wool, that would mean high density.
  • Attach insulation layers to the roof deck in a manner to eliminate thermal breaks. If mechanically fastening the insulation, the fasteners should be covered with another layer of insulation, cover board or both.
  • Design roof covers that do not require mechanical fasteners below the membrane as an attachment method.
  • Protect the thermal layer on top with cover boards and below with appropriate air and vapor barriers.

Saving limited fossil fuels and reducing carbon emissions is a worldwide goal. Designing and installing roof systems with a well thought out, detailed and executed thermal layer will move the building industry to a higher plane. Are you ready for the challenge?

About the author: Thomas W. Hutchinson, AIA, FRCI, RRC, CRP, CSI, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information, visit www.hutchinsondesigngroup.com.

The Stud Wall and the Roof

Photo 1. With a stud wall parapet, inappropriate wall substrate and base anchor screws into a material with low pull-out resistance, this roof blew off in what would be considered moderate winds. Images: HUTCHINSON DESIGN GROUP LTD.

How do I start an article on a topic that is so problematic, yet it’s not being addressed by designers, roof system manufacturers, FM, SPRI, NRCA or any other quality assurance standard? Like many transitions in the building industry, the use of metal studs in exterior wall construction and roofing in new construction developed out of the twin concerns of value engineering and cost reduction. It has crept silently forward without any real consideration of the possible effects this less robust construction method would have on roof system performance. 

Photo 2. When the base anchors pull out of the substrate, the membrane becomes unsecured and will lift up. Here the membrane was observed lifting to heights of 3 to 4 feet, at which point it popped the coping off.

You would think that someone along the line would say, “Hmm, I wonder how strong, effective or appropriate a screw fastener through a modified gypsum board sheathing would be?” Let me answer that question: Worthless. (See Photos 1-3.) 

There are many issues with metal stud wall construction as it relates to roofing: air drive, moisture, interior pressures, and membrane adhesion to substrate, just to name a few. This article will address only one concern: The base anchor attachment horizontally into steel stud walls, most often clad with a modified gypsum substrate board. (See Photo 4.)

Why Is This a Concern?

Photo 3. All the base anchor screws pulled out of the substrate except one that was into the stud, which just tore away when the rest of the membrane lifted.

Problems often begin in the design phase when the condition is not detailed appropriately. (See Figures 1 and 2.) The architect/engineer/ designer shows some lines and figures that the roofing contractor or manufacturer will make it work — and specifies a 20-year warranty. The designer’s first mistake is to think that contractors and manufacturers design. They do not.If I were a betting man, I would guess that 99 percent of the specified wall substrate for roof-side metal stud walls is a product that is unacceptable for roofing base flashing application. You’re smiling now, aren’t you? Been there, huh? Designers often have little knowledge as to how a roof system, or even a roof membrane, is installed, and thus don’t even realize the errors of their ways. If they did, they might realize that at the very least a base anchor attachment is at 12 inches on center, and at some time a screw is going to have to go horizontally into the inappropriate sheathing substrate. Concept 1: Architects design. I know this is scary.

Figure 1. This is a common architectural stud wall parapet detail. No base anchor is even being acknowledged, nor is the concern with vertical vapor drive in the stud wall cavity. This type of detailing, in my opinion, is below the standard of care of the architect.

Architects and designers who do not prepare project-specific details seem to love manufacturers’ standard details, which are provided as a baseline for developing appropriate project-specific details. They are not an end all, and thinking they are is a huge mistake. Another common mistake is not realizing that manufacturers do not have a standard detail for base anchor attachment into metal stud walls. This is probably because they never imagined that anyone would really try to anchor into such a poor substrate. Concept 2: Manufacturers produce products that can be assembled in a roof system; they do not design.

Oh, but the contractor will make it work. Yeah, right. Concept 3: Contractors install materials provided by the manufacturer, as specified by the designer; they do not design. Are you starting to see a trend here?

You can now see the conundrum of the blind leading the blind. 

So, to be clear:

  • Architects: Design
  • Manufacturers: Produce products
  • Contractors: Install materials

To say it a bit clearer:

  • Architects: Design
  • Manufacturers: Do Not Design
  • Contractors: Do Not Design

Read it again and see where the responsibility lies. Of course, the manufacturer needs to produce quality materials, which sometimes does not occur, and contractors need to install the materials correctly, which sometimes does not occur.

Pull-Out Strength

So that we can get this detail correct, let’s look at pull-out strengths of various materials. But let’s start with trying to determine what pull-out resistance is required. For our example, let’s use 60-mil TPO, a common roofing membrane on new construction projects. 

Figure 2. This parapet detail has been well thought out in regard to thermal drive and concerns with condensation within the stud wall cavity, but ignores how the roof membrane will be attached to the wall. The insulation thickness will result in an unbraced section of the screw and allow rotation before it pulls out of what is assumed to be a gypsum base sheathing.

Manufacturers report on their data sheets for 60-mil TPO tear strength of around 130 pounds of force (lbf). The test for this isn’t pulling the membrane out from base anchors, but it’s a good start for our discussion. I suspect that if base anchors are attached at 9 inches or 12 inches on center that the series of fasteners will elevate this value.

Given that we know that the tear resistance of TPO with a series of fasteners is greater than the ASTM D751 Tearing Strength test, I will suggest that we need a substrate with a pull resistance greater than 260 lbf, or twice the tear strength value. After that the membrane will tear itself out from around the fastener plate. 

To determine the pull-out resistance of various sheathing materials, I had the pull-out resistance of a base anchor screw tested on several materials by Pro-Fastening Systems, a specialty distributor focusing on commercial roofing in the Midwest that provides certified pull-out testing. Three pull-out tests were performed on each material. (See Photo 5.) The mean resistance values are as follows:

Photo 4. This exterior view gives a good idea of how inadequate gypsum-related products are in regard to providing a pull-out resistance. A 16-, 18- or 20-gauge plate should have been placed at the stud wall from the concrete deck up above the anchor point.

1/2” plywood: 422 pounds

5/8” plywood: 402 pounds

1/2” glass-faced gypsum: 13.3 pounds

1/2” integral fiber reinforced gypsum: 110 pounds

22-gauge steel deck: 646 pounds

22-gauge acoustical steel deck: 675 pounds

18-gauge steel stud: 1,086 pounds

26-gauge metal stud: 646 pounds

16-gauge steel plate: 1,256 pounds

18-gauge steel plate: 978 pounds

20-gauge steel plate:724 pounds

22-gauge steel plate:625 pounds

So as a starter we eliminate all the typical gypsum-based sheathing materials from being used at the base of the roof. I’m not keen on plywood either, as over time, as the plywood dries, the pull-out strength lessens. Additionally, gluing to wet plywood never works well. 

Designing the Base Anchor on Metal Stud Walls

Photo 5. Various materials were tested to determine their pull-out resistance. The results confirmed what intuitively most roofing contractors would know — that gypsum-based products have very little holding power.

The concept is simple — provide a substrate with a pull-out resistance greater than the tear strength of the roofing membrane attached in series. So, let’s pretend you’re drafting. Come on now, get your paper out, a number 2H pencil, a parallel rule and triangle to get the feel of the detail — no CAD for you today. For our example, assume you’re in the Chicago area, minimum R-value of 30, tapered insulation and 24 feet from the drain to the wall. 

First, draft and show the roof deck and your wall, roof edge and studs. Now you’re ready to start your detail. First go to your roof plan, where you have shown all the tapered insulation, and calculate what the thickness will be at your studs. Remember, code requires thickness within 4 feet of the drain. For our detail, you’re near Chicago and thus the height of a tapered insulation layout might be as follows. For the R-30 at the roof drain with a substrate board, insulation and cover board, let say for simplicity it’s 6.5 inches (1/2-inch cover board + 5.4 inches of code-required insulation + 1/2-inch cover board). Now you need to calculate the tapered insulation. For our example, the distance from drain to wall is exactly 24 feet. With a taper of 1/4-inch per foot tapered that is 6.5 inches (1/4 inch x 24 feet = 6 inches, plus the 1/2-inch starting thickness of the tapered). If you plan to use foam adhesive, add 3/8 inch per layer of foam, and be sure you understand all the layers in a tapered system. So, at the wall, the insulation will be approximately 13 inches. With the screw and plate anchor say, 2 inches above the insulation surface, we have a height of 15 inches. So, let’s say we need a substrate capable of pull-outs at least 18 inches in height from the roof deck.

Figure 3. Design of a stud wall parapet includes delineating all the components and tells the contractor what is expected. Burying such information in the specification does no one any good, as the architect most likely will not know to review the shop drawings to those requirements.

Now, I know you are thinking, “OMG, 18 inches — I can cut in a little 6-inch strip at the top of the insulation.” Don’t do it. The strip will not have any continuity or strength and will often buckle under load. Additionally, this continuous substrate piece needs to be placed on the stud. 

Back to your drafting board. Draw in against your stud a continuous 16-, 18- or 20-gauge galvanized steel plate. Depending if the membrane is to be taken up and over the stud wall or terminated some distance above the roofing, the rest of the wall can be clad in less robust materials. Pick any substrate that is roofing membrane compatible and place it over the continuous steel plate and studs above. Tell the contractor how often you want the substrate anchored.

Figure 4. We often find that a simple isometric drawing showing the construction of stud wall parapets is helpful in informing all the related trades how their work interrelates.

Draw in your substrate board, vapor retarder, insulation (and don’t forget to show and call out the spray foam seal between the insulation and wall, as there is often a void). Bring your membrane to the wall, turn it up 3 inches fully adhered to the substrate and show a plate and screw. Call this plate and screw out and note the spacing on the drawing; I’ve never seen a spec up on the roof. The base flashing can now be delineated coming down over the anchors and out onto the flat. Depending on the material, show a weld or seam tape. Now compare your detail to Figures 3 and 4. Who has properly designed the condition?

Remember

There are many issues and concerns with steel stud walls and roofing. This issue with substrate cladding in regard to the interface with the roofing system is only one that I see again and again on projects that have wind damage issues. By carefully designing the roof termination conditions, taking into account all the possible impacts and then detailing the conditions properly, your standard of care can be met and the owner well served.

About the author: Thomas W. Hutchinson, AIA, FRCI, RRC, CSI, RRP, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information, visit www.hutchinsondesigngroup.com

4 Common Causes of Inadequate Drainage on Low-Slope Roofs

Photo 1. Roof decks with poor slope, drains that are up slope and deck defection can result in excessive ponding. Images: Hutchinson Design Group Ltd.

The stone church in rural Portugal was constructed some 700 years ago. The roofs of the transepts are large stone slabs: 5 feet wide, 10 feet to 12 feet long, and 8 inches thick. How they even made it into place is amazing, but to those like us who think in terms of water, what is even more amazing is the carved-out drainage channels. Moving water off the roof was important to builders 700 years ago in Europe, just as it was to the builders of Machu Picchu and Angkor Wat. Along with many indigenous building methods, the movement of water off roofs and away from buildings is becoming a lost design element.

It is not uncommon to walk upon recently installed roofs and see ponding at gutters, roof drains and across the roof. There are many reasons for this degradation of roof system design, including ignorance. A lack of knowledge by designers, a “roofer or builder will figure it out” mentality, and poor installation procedures can all be to blame.

Ponding water provides visual evidence to the owner that something isn’t quite right, and in some instances, it can result in roof structure collapse. If breaches in the roof membrane exist, standing water can result in excess moisture intrusion. (See Photo 1.) Additionally, water on the roof promotes algae growth that can attack some materials. It also allows for ice to form in winter, creating life safety issues as well as external forces affecting the roof cover.

So, what can you do?

In this article we’ll look at four key conditions on the roof that I see as the most erroneously conceived and installed:

  1. The roof system’s transition to the gutters
  2. Two-way structurally sloped roof decks with roof drains above the low point
  3. Four-way structurally sloped roof decks with drains above the low point
  4. Roof drains on level roof decks with tapered insulation

Accumulated Debris at Gutters

As perhaps you know and will see within this article, there are many things that irk me; one is walking on a new roof and seeing a 3- to 4-foot wide swath of black accumulated dirt and airborne components in front of the gutter. This situation

Photo 2. Owners do not like seeing ponding in front of their gutters, especially when it’s egregious. Proper design and installation would have prevented this problem. Images: Hutchinson Design Group Ltd.

results from restricted water drainage, and it is especially noticeable on reflective roof covers. (See Photo 2.) This restriction of water drainage can be due to several possible factors, including roof edge wood blocking that is too high, insulation that is too low, and the accumulation of roofing material above the slope plane. The roof deck itself can also be set too low.

When designing roof edge gutters, there are key design elements to consider:

  • Wood blocking:In addition to being of appropriate width and anchorage, wood blocking should be sloped to drain, even with sloped roof decks with an elevation 1/4 inch to 3/8 inch below the anticipated roof insulation height. The greatest error I see with most architects is that they do not draw the detail to scale. Insulation is not of the correct thickness, the wood is too big or too small, or it is depicted as one giant block floating atop the wall with no mention of anchorage.
  • Insulation:Please read the ASTM standard for polyisocyanurate and you will learn that the ISO has an allowable dimensional change. Thus, if you specified two layers of 2.25-inch ISO to match three layers of two-by wood blocking, you might be in for a surprise. You might get to the field and see that your two layers of insulation are 3/8 of an inch below the top of the wood, and the manufacturer whom you’ve complained to will pull out the ASTM standard and say, “We are within tolerances.”
  • Material layering:When the roof membrane is taken over the wood (yes you should do this) and sealed to the wall substrate, and the gutter is set in mastic and then stripped in, the accumulated material thickness can exceed 3/8 of an inch. Not much, you say, but on a roof with a 1/4-inch-per-linear-foot slope, that can result in 18 inches of ponding right in front of the gutter. Ouch.

Design recommendations for achieving complete drainage at the roof edge with gutter include:

  • Communicate with the structural engineer.Coordinate with the structural engineer to determine the elevation of the wall (less wood blocking) with the structure and roof deck. If perimeter steel angles attached to the wall rise above the roof deck, discuss with the structural engineer turning the angle downward or changing the angle to one with a vertical leg that doesn’t rise above the roof deck. Angles that rise above the roof deck create a void when

    Photo 3. Even when using tapered insulation and on four-way sloped roof decks, it is advantageous to accentuate the slope into the drain. Here a 1/2-inch-per-foot tapered insulation sump matches up to the tapered insulation with the help if a 1/2-inch tapered edge strip. Images: Hutchinson Design Group Ltd.

    the first layer of insulation is set that is most often not sealed, resulting in a thermal short and a place where dew points can be reached and condensation can occur. If reinforcing paper facers are on the insulation, mold growth can result.

  • Properly detail the wood blocking. I prefer and recommend the use of two layers of wood blocking. First off, do not use treated wood; use untreated Douglas fir. The wood should be at a minimum 8 inches wide (preferably wider) so that the gutter flange can have nail locations back far enough to allow for 3-inch minimum overlap on the stripping-in ply.

Often it is best if the top of the wall is sealed prior to the installation of the wood to prevent air/moisture transport to the wood, and on precast, to prevent the migration of “damp” into the wood. The first layer of wood should be anchored to the structure (wall or framing). While not always required, I prefer to set anchors at 2 feet on center, staggered. This spacing prevents the warping of the wood. The second layer of wood should match the first in width. I suggest that this second layer of blocking be sloped, and placing a continuous shim along the roof side on the first layer will provide the proper slope. The shim width and thickness are dependent on the wood size, but for two-by-ten wood blocking, a shim of 1/2 inch by 1.5 inches will work well. The second layer of wood blocking should be set with joints offset from the lower layer and then screw fastened at 12 inches on center, staggered. Joints on both layers should be scarfed at 45degrees and screwed tight. On your detail, the height of the wood blocking at the interior side above the roof deck should be dimensioned. This will allow contractors to identify height concerns well before the installation of the insulation so adjustments can be made if necessary. I suggest that this distance be 1/4 inch to 3/8 inch below the top surface of the roof insulation or cover board atop the insulation. (See Figure 1.)

  • Make sure the insulation is higher than the wood blocking.We will not discuss insulation types, substrate boards (vapor barriers) and cover boards in this article; please see earlier articles on the topic. In designing the roof edge and discussing/coordinating with the structural engineer, the goal is to have the insulation system: substrate board, vapor retarder, cover board. The thickness should be 3/8 of an inch greater than the interior top corner of the wood blocking. One key item to remember is that spray-and-bead polyurethane adhesive adds 3/8 of an inch thickness per layer. Designing the insulation to be higher than the wood blocking is important, as it compensates for that allowable dimensional change mentioned above, as well as the thickness created by the layers of gutter flange and roofing. The goal is to create a condition in which water will flow over and into the gutter.

Two-Way Structurally Sloped Roof Decks

Often long, narrow roof areas are designed with a two-way structurally sloped roof deck designed to move water from the outer roof edge to a central point. Prudent designers would like the roof drains to be located at the low point of the structurally sloped roof deck. Typically, though, there is a steel beam at the low point, which prevents the installation of the roof drain at the low point. Consequently, the roof drains must be located on the plumbing drawings up slope from the low point. I have tried for years to explain to plumbing engineers that water doesn’t typically flow uphill, but to no avail, so we as the roof system designer have to fix it. How? By moving the low point.

How is this design goal accomplished?

Let’s start with our roof system design for the following example: a new construction project in Chicago (R-30 minimum) with a steel roof deck, two-way structural slope and the low point over a steel beam. The plans call for the drains to be installed 2 feet up slope, and thus they will be more than 1/2 inch above the low point.

The goal will be to move the structural low point to the drain line. With a structural slope, to meet the thermal value we are looking at two layers of 2.6-inch insulation. Run the first layer of 2.6-inch insulation throughout the roof. Then the fun begins: Draw a line down the center of the roof drains. From this centerline, come out 4 feet on each side with a 1/2-inch-per-foot tapered edge board (Q panel, for those who know). The next layer of 2.6-inch insulation abuts the taper. The tapered insulation at the drain line effectively moves the low point to the drains. (See Figure 2.)

Now that the water is being moved to a new low point, it then needs to be moved to the drains. This is accomplished by saddles. (See Figure 3.) Sounds simple enough, but 95 percent of the saddles I see are incorrect, and water ponds on them, over them and along them. This situation leaves, once again, a bad taste in the mouth of the owner, general contractor, construction manager, and architect — even though it’s the designer’s problem. So, I will now, for the first time, reveal my secret developed years ago: The taper of the saddles mustbe twicethe roof deck slope. If the deck slopes 1/4 inch per foot, the saddles must slope at 1/2 inch per foot. If the deck slopes at 3/8 inch per foot, as it often does, the saddle needs to be at 3/4 inch per foot. And, architects and designers, the slope of the saddle is to the valley line, not the drain. The width of the saddle is the key and determining the width of the saddle is my secret.

It’s a simple formula:

(Distance Between Drain)x 33% = X

2

Increase X to the next number divisible by 4

Example: If the drains are 60 feet apart, divide 60 by 2 to get 30 feet; multiply 30 feet by 33% = 9.9 feet. Increase 9.9 to the next number divisible by 4 to get the answer: 12 feet.

Thus, the saddles at the mid-point apex should extend out three full tapered insulation boards. It’s best if you dimension this width on the detail.

On large buildings, the saddle width and thickness can be quite high, so be sure to double-check the insulation height with the height of the roof edge. I could tell you about a roof where the insulation rose several inches above the perimeter height because someone didn’t draw the detail to scale, but that is a story for another time.

Roof Drains in Four-Way Slope Roof Decks

Structurally sloped roof decks can be beneficial in that they can create positive drainage flow. But with four-way structurally sloped roof decks, the drain is not necessarily at the low point of the roof. How far off the low point is dependent on the plumbing contractor. I have seen drains installed several feet upslope. The plumbing drawings should have a note to the fact that the roof drain sump pan should be installed as close to the low point as possible.

Even when the drain is installed very close to the low point, it is still high and will result in water ponding in front of the drain. Thus, the low point needs to be artificially moved to the drain.

This is accomplished with a drain sump. Best practices suggest that the roof insulation be installed in two layers. This will allow for the installation of the sump.

Using Chicago as an example, which calls for R-30 or 5.2-inches of insulation, the first layer of insulation 2.6 inches thick is installed across the roof deck, to the roof drain. It should be cut to the roof drain extension ring. Fill the void between the roof drain and the insulation with spray foam; trim to the insulation. Next the tapered insulation sump is installed. To match the next layer of insulation, we use 1/2-inch-per-foot tapered insulation. It starts at 1/2 inch and, with a 4-foot panel, rises to a thickness of 2.5 inches. Placed around the drain, the sump created is 8 feet by 8 feet. The next layer of insulation is 2.5 inches and abuts the backside of the tapered insulation.

The 1/2-inch-per-foot slope is used as it doubles the slope of the structurally sloped roof deck, which in this case has a slope of 1/4 inch per foot.

Level Roof Decks With Tapered Insulation

Whether re-roofing or new construction, getting the drainage correct on level roof decks is still a challenge for most designers. Perhaps they don’t realize decks are not level; they have camber, they deflect, they undulate, and the drains are often near columns so the drain pipe can run along it. When the drain is near a column where no deflection takes place, it can often be high.

I like to first ensure the proper drain assembly has been selected and designed by the plumbing engineer: the roof drain, reversible collar, threaded extension ring, clamping ring, cast iron dome. (For more detail, see “Roof Drain Installation Tips” on page XX of this issue.) The sump pan should be selected and designed by the plumbing engineer and provided by the roof drain manufacturer — not by the metal deck supplier. (That the industry cannot get this correct is one on my pet peeves.) Do not raise drains off the deck with threaded rods. (See my article “Concise Details and Coordination Between Trades Will Lead to a Quality Long-Term Solution for Roof Drains,” RoofingMay/June 2016). If designing in a vapor retarder, it needs to extend to the roof drain flange and be clamped by the reversible collar. The first layer of insulation should be cut to fit and extend under and to the extension ring. Any voids should be sealed with spray foam.

To compensate for all the potential deck irregularities, I like to accentuate the slope into the roof drain by increasing the taper. More often than not, this means designing a 1/2-inch-per-foot slope sump into the drain. With a 4-foot board, this results in an 8-foot-by-8-foot sump. (See Figure 4 and Photo 3.) After detailing this sump, the main roof four-way tapered insulation can be designed and the heights at the perimeter calculated and noted on the plans. Just a reminder that the code-required thermal value needs to be attained four feet from the drain. So, for Chicago we detail to achieve R-30 at the backside of the tapered sump.

Final Thoughts

A new roof installation that results in ponding water at the drainage point is an unfortunate occurrence. Owners can be upset: “What is that?” “I didn’t pay to have water retained at the drains!” “Who is coming up and cleaning all this stuff off my roof?” Ponding water can be a standard of care issue for designers and result in damages. Learning to properly design rooftop drainage is not difficult, but it requires some thinking and some rooftop experience. Getting up on the roof during installations will help you visualize the needs to achieve proper drainage.

Making sure the roof system drains properly requires discussions with the structural engineers for new construction. I also find it helpful to have the plumbing contractor at pre-con meetings to review the interrelationship of the roofing and drains.

Getting water off the roof as quickly as possible has been a key priority for centuries — no matter the roof cover material. If the builders using stone can achieve complete and full drainage, then I challenge you to achieve it with the materials we use today.

Are You Meeting Thermal Insulation Code Requirements?

Photo 1. Conditions such as this, in which the fastener plates melt the snow, visually demonstrate the heat loss that is a known entity to roof installers and knowledgeable roofing professionals.

You may have overheard conversations such as this:

New Building Owner: “You promised energy conservation and savings.”

Mechanical Engineer: “We sized the mechanical unit based on the code required effective thermal value.”

New Building Owner: “But why are my cost 30 percent above your estimates and I am needing to run my units constantly and they still barely maintain a comfortable environment?”

Mechanical Engineer: “We have checked all the set points and systems and they are all working, albeit with a bit of laboring. We don’t know why there is not enough heat.”

New Building Owner: “Well, someone is going to have to pay for this!”

Scenarios and liability questions like this are being repeated across the northern North American continent, and to mechanical engineers, architects and owners, the cause is a mystery. Perhaps they should have talked to seasoned roofing professionals and consultants. They could’ve told them that many mechanically attached roofs, incorrectly promoted and sold as energy-saving systems, were actually energy pigs. One only needed to walk a mechanically attached roof with a few inches of snow on it to see the heat loss occurring. It doesn’t take scientific studies and long-winded scenarios to prove this — just get up on the roof and see it. (See Photo 1.)

Photo 2. When a light dusting of snow blew off this 2 million-square-foot facility in central Illinois, every single mechanical fastener and insulation joint could be identified by the ice visible at their locations. This roof needed to be replaced due to condensation issues several years after installation at a cost of more than $10 million.

I spoke on this topic back in 2007 at the RCI Cool Roofing Symposium. I always like being a soothsayer, and several recent studies are demonstrating and attempting to quantify this energy loss that most roofers could tell you was there.

For years the NRCA suggested a loss of thermal value of 7 percent to 15 percent through the joints in a single-layer insulation application and through mechanical fasteners used to secure the insulation. (The NRCA has since removed this figure and suggests that professionals be consulted to determine thermal heat loss.) The NRCA recommended a cover board to reduce this effect. This was at a time when roof covers were predominantly BUR, modified bitumen or adhered single plies. The upsurge in mechanically attached single-ply membranes, brought on by low-cost installation and the promise of energy savings, changed the game. No one was asking, if there could be a loss of 7-15 percent when mechanically attaching insulation, what could the effective R-value loss be when we install thousands of fasteners and plates 12 inches on center (or less) down a membrane lap seam? Gee, haven’t we seen that before?

Code Requirements

The code and standard bodies — ICC, IECC, ASHRAE — have been repeatedly raising required thermal insulation values over the past decade in an attempt to conserve energy; that is their intent. They listened to astute designers and

Photo 3.This is close-up of the roof shown in Photo 2. Heat loss through the screws and fastener plates and through joints in the single layer of insulation melted the snow. The water froze when the temperatures dropped and the ice was revealed when a light wind pillowed the membrane and the remaining snow blew away.

prescribed two layers of insulation, and then again to determine the minimum R-value and not allow averages. The intent is clear. The required R-value per ASHRAE zone is to be achieved.

Their goals were laudable, but not all roof systems achieved the in-place R-values required. So, this article is in part an attempt to educate code officials and explain the need for a change.

Words can explain the phenomenon of thermal loss, but photos are worth a thousand words, and since my editor has told me that I cannot have a 4,000-word article, I leave it to the photos to do the talking. (See Photos 2, 3 and 4.)

Scientific Studies

In their Buildings 2016 article titled “Three-Dimensional Heat Transfer Analysis of Metal Fasteners in Roofing Systems,” Singh, Gulati, Srinivasan and Bhandari (Singh) studied the effect of heat transfer through thermal bridging (mechanical fasteners) in various roof assembly scenarios.

Their study exposes a shortfall in many standards that have as their goal a reduction in energy loss through building envelope systems through prescriptive approaches. For roofing assemblies, standards prescribe a minimum R-value, but they do not take into consideration the heat loss that happens though metal fasteners. There are no guidelines or recommendations in regards to thermal loss, including the loss of heat through roof system fasteners. It’s actually ignored.

Figure A: The effect of mechanical fasteners below the roof cover in mechanically attached roofs is not negligible as considered by general standards. As can be seen here for systems 1A and 1 B, in which mechanical fasteners are used in the lap seams of the roof cover (systems 3A and 3B have the fasteners below a layer of insulation), the actual thermal value loss caused by mechanical fasteners can be as high as 48 percent, as seen in system 1A with a high density of mechanical fasteners. As the mechanical fastener density decreases (1B), the heat loss also decreases. Thus, a correlation appears to exist in which heat loss due to thermal bridging is proportional to the fastener density.

The results of the Singh study, as seen in the graph (Figure A), show that the effects of thermal shorts, e.g., mechanical fasteners used to secure the roof cover, is not negligible. In fact, thermal shorts can result in a loss of 48 percent of the effective value. Read that again! The thermal value of the roof insulation layer on which the mechanical engineer has in part sized the mechanical equipment — and which the owner is counting on for significant energy savings — could be about half of what was assumed. Add in gaps and voids, and the loss in the effective R-value could top 50 percent. What that means is that to achieve the code required R-30, say in Chicago, mechanically fastened roof systems need to have R-45 in the design to meet the effective code required R-value. This last sentence is for the code bodies — are you listening?

The value of this study cannot be underestimated, as thousands of buildings have been constructed since its publication that would not meet an effective R-value check in a commissioning study.

Changing the Code

The energy inefficiency of mechanically attached roof systems in ASHRAE zones 4 and above has been known to roofing crews for decades. Now, with the requisite scientific studies completed, the codes need to be revised to reflect the inherent thermal loss through mechanical fasteners. Additionally, studies from Oak Ridge National Laboratory highlight the energy increase required with inherent air changes below the membrane, confirming the need for air/vapor barriers on the deck on mechanically attached roof assemblies. (See “The Energy Penalty Associated with the Use of Mechanically Attached Roofing Systems,” by Pallin, Kehrer and Desjarlais.)

Photo 4: Heat loss also occurs through adhered roofs when the insulation is mechanically attached.

As a starting point for code groups and officials, I suggest the following code revisions:

  1. State that if a mechanically attached roof cover is being used that the prescribed thermal R-value shall be increased by 50 percent.
  2. State that if a mechanically attached roof cover is being used that an air barrier below the insulation must be used and that it shall be fully adhered to penetrations and roof perimeters.

Closing Thoughts

The goal of energy conservation is a laudable one. The American Institute of Architects’ goal of zero-energy building by 2030 will never be met until real-world empirical information can be presented at code hearings. (For those of you who do not attend code hearings or know the process, information is usually disseminated in two-minute sound bites without documentation.) This lack of information sharing is a travesty and has resulted in numerous code changes that have been detrimental to the goal of energy savings. Time has come for a new way of thinking.

Single-Ply Roofing Best Practices: Doing Everything Right the First Time.

Figure 1: Designing resilient roof systems is the best of practices. When developing details, we find it very helpful to draft out the roof system (for each different system), noting materials and installation methods. Photos: Hutchinson Design Group

Single-ply membranes have risen from being the “new guy” in the market in the early ’80s to become the roof cover of choice for most architects, consultants and contractors. Material issues have for the most part been resolved, and like no other time in recent history, the industry is realizing a period of relative calm in that regard. Whether EPDM, TPO or PVC, the ease of installation, the cleanliness of the installation (versus the use of hot or cold bitumen), the speed at which they can be installed, and the material costs all blend to make these materials a viable option for watertight roofing covers. But with this market share comes issues and concerns, some of which are hurting owners, giving forensic consultants such as myself too much business, enriching attorneys, and costing contractors and, at times, designers dearly.

Following are some of my thoughts on various issues that, in my opinion, are adversely affecting single-ply membrane roof systems. Paying attention to these issues will bring about best practices in single-ply applications.

Specifying the Roof by Warranty

OMG, can architects do any less? Don’t get me started. The proliferation of “canned” Master Specs which call for a generic 10-year or 20-year warranty and then state to install the product per manufacturer’s guidelines is disheartening. Do

Figure 2: Coordinating with the mechanical engineer in the detailing of the pipe penetrations is critical. Here you can see all the components of the curb, penetrations, roofing and waterproofing are noted. We recommend that the same detail be on the mechanical sheets so that at least an 18-inch curb is known to all. Photos: Hutchinson Design Group

designers realize that manufacturers’ specifications are a market-driven minimum? When architects leave out key details, they are simply relying on the roofing contractor to do what is right. This deserves another OMG. The minimum requirements for a warranty can be very low, and the exclusions on a warranty quite extensive. Additionally, a design that calls for products to be installed based on achieving a warranty may result in a roof system that does not meet the code. Owners are often oblivious to the warranty requirements, and all too often fail to ensure the standard of care until the service life is shortened or there is storm damage — sometimes damage the roof should have withstood if it were properly designed and detailed.

If one is not knowledgeable about roof system design, detailing and specification, then a qualified roof consultant with proven experience in single-ply membranes should be retained. Roof systems and their integration into the impinging building elements need to be designed, detailed and specified appropriately for the building’s intended use and roof function. By way of example, we at Hutchinson Design Group typically design roof systems for a 40- to 50-year service life (see Figure 1); the warranty at that point is nice, but almost immaterial. Typical specifications, which are project specific, cover all the system components and their installation. They are typically 30 pages long and call out robust and enhanced material installations.

More Than the Code

I recently had a conversation with a senior member of a very large and prominent architectural firm in the Chicago area and inquired about how they go about designing the roof systems. The first thing he said was, “We do what is required by code.”

Photo 1: The roof drain sump pans shown here were provided and installed by the plumbing contractor, not the steel deck installer. Having the roof drain level with the top of the roof deck allows for a proper integration of the roof drain and roof system.

What I heard was, “We give our clients the absolute poorest roof the code allows.” An OMG is allowed here again. Does it really need to be said again that the code is a minimum standard — as some would say, the worst you are allowed to design a building by law? Maybe you didn’t realize it, but you are allowed to design above the code. I know this will shock a few of you, but yes, it’s true. Add that extra anchor to prevent wood blocking from cupping. Add extra insulation screw fasteners to improve wind uplift resistance; if too few are used, you may meet the code, but your insulation will be susceptible to cupping. Add that extra bead of polyurethane adhesive. (If I specify 4 inches on center, then perhaps by mid-day, on a hot and humid day, I might get 6 inches on center — as opposed to specifying 6 inches or 8 inches on center, and getting 12 inches on center in spots.) Plan for construction tolerances such as an uneven decks and poorly constructed walls. Allow for foot traffic by other trades. These types of enhancements come from empirical experiences — otherwise known as getting your butt in the ringer. Architects need more time on the roof to observe what goes on.

It’s About Doing What is Right

Doing it right the first time isn’t all that difficult, and it’s certainly less stressful than dealing with the aftermath of doing so little. The cost of replacing the roof in the future could easily be more than double the original cost. Twenty years ago, I

Figure 3: Coordinating with the plumbing engineer, like coordinating with the mechanical engineer, is a requirement of best practices. In this drain detail, we can see the sump pan is called out correctly, and the roof drain, integration of the vapor barrier, extension ring, etc., are clearly defined. Photos: Hutchinson Design Group

chaired an international committee on sustainable low-slope roofing. At that time, the understanding of sustainability was nil, and I believe the committee’s Tenets of Sustainability, translated into 12 languages, helped set the stage for getting designers to understand that the essence of sustainability is long-term service life. That mantra seems to have been lost as a new generation of architects is at the helm. This is unfortunate, as it comes at a time when clients no longer ask for sustainable buildings. Why? Because they are now expected. The recent rash of violent and destructive storms — hurricanes, hail, intense rain, high winds and even wildfires — have resulted in calls for improvement. That improvement is called resiliency. If you have not heard of it, you are already behind. Where sustainability calls for a building to minimize the impact of the building (roof) on the environment, resiliency requires a building (roof) to minimize the impact of the environment on the building. This concept of resiliency requires designing a roof system to weather intense storms and to be easily repaired when damaged. (Think of Puerto Rico and consider how you would repair a roof with no power, limited access to materials, and manpower that might not be able to get to your site.)

Achieving resiliency requires the roof system designer to:

  1. Actually understand that roofs are systems and only as good as their weakest link. Think metal stud parapet and horizontal base anchor attachment; only forensic consultants and attorneys like to see screws into modified gypsum boards.
  2. Eliminate your old, out-of-date, incorrect details. Lead vent flashing and roof cement cannot be used with single-ply membrane.
  3. Design the roof system integration into associated barrier systems, such as where the roofing membrane (air/vapor retarder) meets the wall air barrier. You should be able to take a pencil and draw a line over the wall air barrier, up the wall and onto the roof without lifting it off the sheet. If you cannot, you need to redesign. Once you can, you need to consider constructability and who may get there first — the roofer or air barrier contractor. Then think material compatibility. Water-based air barrier systems don’t react well when hit with a solvent-based primer or adhesive.

    Photo 2: This roof drain is properly installed along with 6 inches of insulation and a cover board. The drain extension ring is 1/2 inch below the top of the cover board so that the water falls into the drain and is not held back by the clamping ring, resulting in ponding around the roof drain.

    Perhaps the roofing needs to be in place first, and then the air barrier brought over the top of the roofing material. This might require a stainless-steel transition piece for incompatible materials. Maybe this requires a self-adhering membrane over the top of the roof edge prior to the roofing work, as some membranes are rather rigid and do not bend well over 90-degree angles. You as the designer need to design this connectivity and detail it large and bold for all to see.

  4. Design the roof system’s integration into the impinging building elements, including:
  • Roof curbs for exhaust fans: Make sure they are insulated, of great enough height, and are not installed on wood blocking.
  • Rooftop unit (RTU) curbs: The height must allow for future re-roofing. Coordinate with the mechanical engineer regarding constructability – determine when the curb should be set and when the HVAC unit will be installed. Roof details should be on both the architectural and mechanical drawings and show the same curb, drawn to scale. Be sure the curb is insulated to the roof’s required R-value. Avoid using curb rails to support mechanical equipment. The flashing on the interior side of the rails may be inaccessible once the equipment is placed. Use a large curb where all four sides will remain accessible.
  • Piping penetrations: Detail mechanical piping penetrations through the roof and support of same, where insulation and waterproofed pipe curbs are needed (see Figure 2). If you are thinking pourable sealer pocket, stop reading and go sign up for RCI’s Basics of Roof Consulting course.
  • Roof curbs, RTU, pipe curbs and rails: Coordinate their location and show them on the roof plan to be assured that they are not inhibiting drainage.
  • Roof drains: Coordination with the plumbing engineer is essential. Sump pans should be installed by the plumbing contractor, not the steel deck installer (see Photo 1), and the location should be confirmed with the structural engineer. Be sure drains are located in the low point if the roof deck is structurally sloped — and if not, know how to design tapered insulation systems to move water up that slope. Do not hold drains off the deck to meet insulation thickness; use threaded extensions. Be sure any air/vapor barrier is integrated into the curb and that the insulation is sealed to the curb. I like to hold the drain flange a half-inch down below the insulation surface so that the clamping ring does not restrain water on the surface. Owners do not like to see a 3-foot black ring at the drain, where ponding water accumulates debris (see Figure 3 and Photo 2).
  1. Understand the roof’s intended use once the building is completed. Will the roof’s surface be used for anything besides weather protection? What about snow removal? Will there be excessive foot traffic? What about mechanical

    Photo 3: Gaps between the roof insulation and roof edges, curbs and penetrations are prevalent on most roofing projects and should be sealed with spray foam insulation as seen here. It will be trimmed flush once cured.

    equipment? Photovoltaic panels? Yes, we have designed roofs in which a forklift had to go between penthouses across the roof. Understanding how the roof will be used will help you immensely.

  2. Understand the construction process and how the roof might be used during construction. It is amazing how few architects know how a building is built and understand construction sequencing and the impact it can have on a roof. I firmly believe that architects think that after a lower roof is completed, that the masons, carpenters, glazers, sheet metal workers, welders, pipe fitters, and mechanical crews take time to fully protect the newly installed systems (often of minimal thickness and, here we go again, without a cover board — OMG) before working on them. I think not. Had the architect realized that temporary/vapor retarders could be installed as work surfaces, getting the building into the dry and allowing other trades to trash that rather than the finished roof, the roof system could be installed after those trades are off the roof.
  3. Coordinate with other disciplines. Roof systems cannot be designed in a vacuum. The architect needs to talk to and involve the structural, mechanical and plumbing engineers to ensure they realize the importance of essential details. For example, we cannot have steel angle around the drain whose flange rests on the bar joist, thus raising the roof deck surface at the roof drain. Ever wonder why you had ponding at the drain? Now you know. I attempt to always have a comprehensive, specific roofing detail on the structural, mechanical and plumbing sheets. I give the other disciplines my details and ask that they include them on their drawings, changing notes as required. That way, my 20-inch roof curb on the roof detail is a 20-inch curb on the mechanical sheets — not a standard 12-inch curb, which would more often than not be buried in insulation.
  4. Detail, detail, detail, and in case you glossed over this section, detail again. Make sure to include job-specific, clearly drawn details. Every condition of the roof should be detailed by the architect. Isn’t that what the client is paying for? Do not, as I once saw, indicate “RFO” on the drawings. Yes, that acronym stands for “Roofer Figure Out.” Apparently, the roofer did not figure it out. I enjoyed a nice Hawaiian vacation as a result of my work on that project, courtesy of the architect’s insurance company. How do you know that a condition works unless you design it and then draw it to scale?

    Figure 4: Insulation to curbs, roof edge and penetrations will not be tight, and to prevent a thermal short, the gaps created in construction need to filled with spray foam, as noted and shown here in this vent detail. Photos: Hutchinson Design Group

    I’ve seen roof insulation several inches above the roof edge because, OMG, the architect wanted gravel stop and forgot about camber. Not too big a deal (unless of course it’s a large building) to add several more layers of wood blocking and tapered edge strips at the now high wood blocking in the areas that were flush, but now the face of the roof edge sheet metal needs to increase. But what if the increase is above the allowable ANSI-SPRI ES1 standard and now a fascia and clip are required? You can see how the cost spirals, and the discussion ensues about who pays for what when there is a design error.

  5. Develop comprehensive specifications that indicate how the roof system components are to be installed. This requires empirical knowledge, the result of time on the roof observing construction. It is a very important educational tool that can prevent you, the designer, from looking like a fool.

Components

Best practices for single-ply membranes, in addition to the design elements above, also involve the system components. Below is a listing of items I feel embodies best practices for single-ply roof system components:

  1. Thicker membranes: The 45-mil membrane is insufficient for best practices, especially when one considers the thickness of the waterproofing over scrim on reinforced sheets. A 60-mil membrane is in my opinion the best practices minimum. Hear that? It’s the minimum. You are allowed to go to 75, 80 or 90 mils.
  2. Cover boards: A cover board should be specified in fully adhered and mechanically attached systems. (Ballasted systems should not incorporate a cover board.) Cover boards have enhanced adhesion of the membrane to the substrate over insulation facers and hold up better under wind load and hail. Cover boards also protect the insulation

    Photo 4: The greatest concern with the use of polyurethane adhesives is that the insulation board might not be not fully embedded into the adhesive. Weighting the boards at the corners and center with a minimum of 35 pounds for 10 minutes has proven to work well in achieving a solid bond.

    from physical damage and remain robust under foot traffic, while insulation tends to become crushed. Cover boards are dominated by the use of mat-faced modified gypsum products. Hydroscopic cover boards such as fiberboards are not recommended.

  3. Insulation: Now here is a product that designers seldom realize has many parts to be considered. First, let’s look at compression strength. If you are looking to best practices, 25 psi minimum is the way to go. The 18-psi insulation products with a fiber reinforced paper facer can be ruled out entirely, while 20 psi products are OK for ballasted systems. Now let’s look at facers. If you think about it for a second, when I say “paper-faced insulation,” you should first think “moisture absorbing” and secondly “mold growth.” Thus paper-faced products are not recommended to be incorporated if you are using best practices. You should be specifying the coated glass-faced products, which are resistant to moisture and mold resistant. A note to the manufacturers: get your acts together and be able to provide this product in a timely manner.

Additional considerations regarding insulation:

  • Insulation joints and gaps: You just can’t leave joints and gaps open. Show filling the open joints at the perimeter and curbs and around penetrations with spray foam in your details and specify this as well (see Photo 3 and Figure 4).
  • Mechanical attachment: Define the method of attachment and keep it simple. On typical projects, I commonly specify one mechanical fastener every 2 square feet over the entire roof (unless more fasteners are needed in the corners). Reducing the number of fasteners in the field compared to the perimeter can be confusing for contractors and the quality assurance observer, especially when the architect doesn’t define where that line is. The cost of the additional screws is nominal compared with the overall cost of the roof.
  • Polyurethane foam adhesive: Full cover spray foam or bead foam adhesive is taking over for asphalt, at least here in the Midwest, and I suspect in other local markets as well. The foam adhesive is great. It sticks to everything: cars, skylights, clerestories, your sunglasses. So, it is amazing how many insulation boards go down and don’t touch the foam. You must specify that the boards need to be set into place, walked on and then weighted in place until set. We specify five 35-pound weights (a 5-gallon pail filled with water works nicely), one at each corner and one in the middle for 10 minutes (see Photo 4). Yes, you need to be that specific.
  1. Photo 5: The design of exterior walls with metal studs that project above the roof deck is a multi-faceted, high-risk detail that is often poorly executed. Here you can see a gap between the deck and wall through which warm moist air will move and result in the premature failure of this roof. The sheathing on the wall cannot hold the horizontal base anchor screw, and the joints in the board allow air to pass to the base flashing, where is will condense. This is the type of architectural design that keeps on giving — giving me future work.

    Vapor/air barrier: A vapor air barrier can certainly serve more than a function as required for, say, over wet room conditions: pools, locker rooms, kitchens, gymnasiums. We incorporate them in both new construction and re-roofing as a means of addressing construction trade phasing and, for re-roofing, allowing time for the proper modification of existing elements such as roof edges, curbs, vents, drains, skylights and pipe curbs. Be sure to detail the penetrations and tie-ins with wall components.

  2. Deck type: Robust roof decks are best. Specify 80 ksi steel roof decks. Try staying away from joint spacing over 5 feet. Decks should be fully supported and extend completely to roof edges and curbs.
  3. Roof edge design: A key aesthetic concern, the termination point for the roof system, the first line of defense in regard to wind safety — the roof edge is all of these. The construction of the roof edge on typical commercial construction has changed drastically in the last 20 years, from brick and block to metal stud. Poorly designed metal stud parapets will be funding my grandkids’ college education. The challenge for the metal stud design is multifaceted: It must close off the chimney effect, prevent warm moist air from rising and condensing on the steel and wall substrate, create an acceptable substrate on the stud face in which to accept base anchor attachment, and — oh, yes — let’s not forget fire issues. Tread lightly here and create a “big stick” design (see Photo 5).
  4. Roof drains and curbs: As discussed above, there is a great need for coordination and specific detailing here. The rewards will be substantial in regard to quality and efficiency, minimizing time spent dealing with “what do we do now” scenarios.
  5. Slope: Design new structures with structural roof deck slope, then fine tune with tapered insulation.

Final Thoughts

Best practices will always be a balancing act between cost and quality. I believe in the mantra of “doing it right the first time.”

The industry has the material and contractors possess the skill. It’s the design and graphic communication arm that needs to improve to keep everyone working at the top of their game.

Designers, get out in the field and see the results of your details. See firsthand how a gypsum-based substrate board on a stud wall does not hold screws well; how a lap joint may not seal over the leading edge of tapered insulation; how the roof either ponds water at the roof drain or doesn’t meet code by drastically sumping; or how the hole cut in the roof membrane for the drain might be smaller than the drain bowl flange, thus restricting drainage. Seeing issues that the contractors deal with will help you as the designer in developing better details.

Contractors, when you see a detail that doesn’t work during the bidding, send in an RFI and not only ask a question, but take the time to inform the architect why you don’t think it will work. On a recent project here in Chicago, the architect omitted the vapor retarder over a pool. The contractor wrote an explicit explanation letter and RFI to the architect during bidding, and the architect replied, “install as designed.” In these situations, just walk away. For me, this is future work. A local contractor once told me, “I don’t get paid to RFI, I get paid to change order.” He also said, “If I ever received a response to an RFI, I would frame it!”

Manufacturers, too, can raise the bar. How about prohibiting loose base flashings at all times, and not allowing it when the salesman says the competition is allowing it. Have contractors on the cusp of quality? Decertify them. You don’t need the hassles. Owners don’t need the risk.

Seek out and welcome collaboration among contractors, roof systems designers, knowledgeable roof consultants, and engineers. Learning is a lifelong process, and the bar is changing every year. Too often we can be closed off and choose not to listen. At HDG, I am proud to say we have the building owners’ best interests at heart.

By all working together, the future of single-ply membranes can be enhanced and the systems will be retained when the next generation of roof cover arrives — and you know it will.

Roofing in Romania, Part II: Past as Prologue

[Editor’s Note: In May, Thomas W. Hutchinson presented a paper at the 2017 International Conference on Building Envelope Systems and Technologies (ICBEST) in Istanbul, Turkey, as did his good friend, Dr. Ana-Maria Dabija. After the conference, Hutchinson delivered a lecture to the architectural students at the University of Architecture in Bucharest, Romania, and spent several days touring Romania, exploring the country’s historic buildings and new architecture. Convinced that readers in the United States would appreciate information on how other countries treat roofing, he asked Dr. Dabija to report on roof systems in Romania. The first article, “Roofing in Romania: Lessons From the Past,” was published in the July/August issue of Roofing. In this follow-up article, Dr. Dabija continues her exploration of the forces shaping the architecture of Romania.]

A late 19th or early 20th century residential building in Bucharest. Photo: Ana-Maria Dabija.

(Photo 1) A late 19th or early 20th century residential building in Bucharest. Photo: Ana-Maria Dabija.

In buildings as well as in other fields of activity, there are at least three determinant factors in the choice of products:

  1. The technology. A key driving force is the technology that improves a product or system. Some systems are not at all new—the ones that use solar power, for instance—but are periodically forgotten and rediscovered; this is another story. The history of past performance is important here as well, as is the skill of the contractors installing the material or system. Technological advancements can mark important developments in industry, but the field is littered with “new and improved” products that never panned out, failed and are out of the market.
  2. The economy. The state of the economy is directly related to the state of the technology; better efficiency in the use of a type of resource leads to the use of more of that resource, as well as to a change of human behavior that adapts to the specific use of the resource. This dynamic is referred to as “the Jevons paradox” or “the rebound effect.” In a nutshell, William Stanley Jevons observed, in his 1865 book “The Coal Question,” that improvements in the way fuel is used increased the overall quantity of the utilized fuel: “It is a confusion of ideas to suppose that the economical use of fuel is equivalent to diminished consumption. The very contrary is the truth.” On the other hand, it seems that innovation is mainly accomplished in periods of crisis, as a crisis obliges one to re-evaluate what one has and to make the best of it.
  3. The political will. As one of the great contemporary architects, Ludwig Mies van der Rohe, stated, “Architecture is the will of the epoch translated into space.”

Like many other things, buildings can be read from the perspective of these factors. And so we go back to square one: history.

(Photo 2) Palace of the National Bank of Romania (1883-1900), designed by architects Cassien Bernard, Albert Galleron, Grigore Cerkez, and Constantin Băicoianu. Photo: Ana-Maria Dabija.

Our excursion in the history of the roofing systems in Romania moves from the 19th century to the present. As mentioned in the previous article, the use of metal sheets and tiles began sometime in the late 17th century (although lead hydro-insulation seems to have been used in the famous Hanging Gardens of Babylon in the sixth or seventh century, B.C.).

The Industrial Revolution that spread from the late 18th to the mid 19th century included the development of iron production processes, thus leading to the flourishing of a new range of building materials: the roofing products. The surfaces that can be covered with metal elements—tiles or sheets—span from low slopes to vertical. More complicated roofs appeared, sometimes combining different systems: pitched or curved roofs use tiles while low slopes are covered with flat sheets.

Copper, painted or galvanized common metal, zinc or other alloys cut in tiles and sheets, with different shapes or fixings—the metal roofs of the old buildings are a gift to us, from a generation that valued details more than we do, today (Photo 1).

(Photo 3) The Palace of the School of Architecture in Bucharest, designed by architect Grigore Cerchez. Photo: Ana-Maria Dabija.

In the second half of the 19th century, in 1859, two of the historic Romanian provinces—Walachia and Moldova—united under the rule of a single reigning monarch, and, in 1866, a German prince, Karl, from the family of Hohenzollern, became king of the United Principalities. In 1877 the War of Independence set us free from the Turkish Empire and led to the birth of the new kingdom of Romania. The new political situation led to the need of developing administrative institutions as well as cultural institutions, which—in their turn—needed representative buildings to host them. In only a few decades these buildings rose in all the important cities throughout the country.

The influence of the French architecture style is very strong in this period as, in the beginning, architects that worked in Romania were either educated in Paris or came from there. It is the case with the Palace of the National Bank of Romania (Photo 2), designed by two French architects and two Romanian ones.

(Photo 4) A detail of the inner courtyard and roof at the Central School by architect Ion Mincu, 1890. Photo: Ana-Maria Dabija.

The end of the 19th century is marked by the Art Nouveau movement throughout the whole world, with particular features in architecture revealing themselves in different European countries. In Romania, the style reinterprets the features of the architecture of the late 1600s, thus being called (how else?) the Neo-Romanian style. A few fabulous examples of this period that can be seen in Bucharest include the Palace of the School of Architecture (Photo 3), the Central School (Photo 4), the City Hall (Photo 5). Most of the roofs of this period use either clay tiles or metal tiles and metal sheets (Photos 6 and 7).

In parallel with the rise of the Art Nouveau style in Europe, the United States created the Chicago School, mainly in relation to high-rise office buildings. This movement was reinterpreted in the international Modernist period (between the two World Wars).

As a consequence of the Romanian participation in the First World War, in 1918 Basarabia (today a part of the Republic of Moldova, the previous Soviet state of Moldova), Bucovina (today partly in Ukraine) and Transylvania were united with Romania. The state was called Greater Romania. The capital city was Bucharest. Residential buildings as well as administrative buildings spread on both sides of the grand boulevards of the thirties, built in a genuine Romanian Modernist style (Photo 8).

(Photo 5) Bucharest City Hall, by architect Petre Antonescu 1906-1910. Photo Joe Mabel, Creative Commons Attribution.

Influences from the Chicago School are present in the roof types. Flat roofs began to be used, sometimes even provided with roof gardens (although none have survived to our day). It is probable that the hydro-insulation was a “layer cake” of melted bitumen, asphalt fabric and asphalt board, everything topped with a protection against UV and IR radiation. The “recipe” was mostly preserved and used until the mid-90s.

In the second half of the 20th century, the most common roofs were the bitumen membranes, installed layer after layer. Residential buildings and most administrative buildings had flat roofs. Still, in the center of the cities, more elaborate architecture was designed, so next to a church with a metallic roof, you might find a residential block of flats with pitched roofs covered with metal tiles, behind which the lofts are used as apartments (Photo 9).

Most of the urban mass dwellings, however, were provided with flat roofs (Photo 10). Even the famous House of the People (Photo 11)—the world’s second-largest building after the Pentagon—has flat roofs with the hydro-insulation made of bitumen (fabric and board layers).

(Photo 6) Residential buildings built in the late 19th or early 20th century in the center of Bucharest. Photo: Ana-Maria Dabija.

Corrugated steel boards or fiberboards were mainly used in industrial buildings and sometimes in village dwellings, replacing the wooden shingles as a roofing solution that could be easily installed (Photo 12).

After 1989, when the communist block collapsed, products from all over the world entered the market. The residential segment of the market exploded, as wealthy people wanted to own houses and not apartments. Pitched roofs became an interesting option, and the conversion of the loft in living spaces was also promoted. Corrugated steel panels, with traditional or vivid colors, invaded the roofs, serving as a rapid solution both for new and older buildings that needed to be refurbished. Skylights, solar tunnels and solar panels also found their way onto the traditional roofs as the new developments continued (Photo 13).

Today the building design market is mainly divided between the residential market and the office-retail market. Where roofs are concerned, unlike the period that ended in 1989 (with a vast majority of buildings with flat roofs, insulated with bitumen layers), most individual dwellings and collective dwellings with a small number of floors (3-4) are provided with pitched roofs, mainly covered with corrugated steel panels.

(Photo 7) The Minovici Villa, architect Cristofi Cerchez, 1913. Photo: Camil Iamandescu, Creative Commons Attribution.

For the high-rise buildings, the bitumen membranes (APP as well as SBS) are still the most common option, but during the past decade, elastomeric polyurethane and vinyl coatings have also been installed, with varying degrees of success. EPDM membranes, more expensive than the modified bitumen ones, are used on a smaller scale. PVC membranes have also been a choice for architects, as in the case of the “Henry Coandă” Internațional Airport in Bucharest. Bitumen shingles also cover the McDonalds buildings and other steep-slope roofs. In the last few years, green roofs became more interesting so, more such solutions are beginning to grow on our buildings.

The roof is not only the system that protects a building against weathering; today it is an important support for devices that save or produce energy. It will always be the fifth façade of the building, and it will always represent a water leakage-sensitive component of the envelope that should be dealt with professionally and responsibly. To end the article with a witty irony, the great American architect Frank Lloyd Wright is supposed to have said, “If the roof doesn’t leak, the architect hasn’t been creative enough.”

(Photo 8) The Magheru Boulevard in Bucharest. Photo: Ana-Maria Dabija.

(Photo 9) Apartment buildings of the late 20th century in Bucharest. Photo: Ana-Maria Dabija

(Photo 10) Mass dwelling building of the mid-1980s. Photo: Ana-Maria Dabija.

(Photo 11) The House of the People (today the House of the Parliament) is still unfinished. The main architect is Anca Petrescu. Photo: Mihai Petre, Creative Commons Attricbution CC BY-SA 3.0.

(Photo 12) Corrugated fiberboard on a traditional house in the Northern part of Romania. Photo: Alexandru Stan.

(Photo 13) The roof of the historic building of the Palace of the School of Architecture, with skylights, sun tunnels and BIPV panels. Photo: Silviu Gheorghe.

Roofing in Romania: Lessons From the Past

[Editor’s Note: In May, Thomas W. Hutchinson presented a paper at the 2017 International Conference on Building Envelope Systems and Technologies (ICBEST) in Istanbul, Turkey, as did his good friend, Dr. Ana-Maria Dabija. After the conference, Hutchinson delivered a lecture to the architectural students at the University of Architecture in Bucharest, Romania, and spent several days touring Romania, exploring the country’s historic buildings and new architecture. Convinced that readers in the United States would appreciate information on how other countries treat roofing, he asked Dr. Dabija to report on roof systems in Romania in the first of what is hoped to be a series of articles on roofing in foreign countries.]

Photo 1. Sanctuary in Sarmizegetusa Regia. Photo: Oroles. Public Domain.

Photo 1. Sanctuary in Sarmizegetusa Regia. Photo: Oroles. Public Domain.

Romania is somewhere in the Southeastern part of Europe, in a stunning landscape: an almost round-shaped country, with a crown of mountains—Carpathians—that close the Transylvanian highlands, with rivers that flow towards the plains, that merge into the Danube and flow to the Black Sea.

Conquered by the Romans in 106 A.D, crossed by the migrators between the fourth and the eighth centuries, split in three historic provinces—Walachia, Moldova and Transylvania—and squeezed between empires, Romania absorbed features from all the people and civilizations that passed through or stayed in its territories.

The language—Latin in its structure—has ancient Dacian words that blend in with words from languages from other countries that had influence in our history: Greek, French, Turkish, English, Slavonic, Serbian, German, Hungarian. Traditional foods vary by region; for instance, in Transylvania you won’t find fish, while at the seaside, in the Danube Delta, on the banks of the rivers, fish is traditional. Each historic province uses different ingredients and developed recipes that can be found in Austria and Hungary, in Greece and Turkey, in Russia and Ukraine.

The same applies to buildings. In Transylvania, the Austrian Empire hallmarked the houses in the villages, the mansions, the palaces, the churches, the administrative buildings. One of the most popular sites for foreign tourists is the Bran Castle, infamous home of Dracula. In Walachia, the buildings have strong Balkan influences. Close to the Black Sea, the Turkish and the Greek communities that settled there brought the style of the countries they came from. Moldova was under the influence of the Russian Empire reaching back to Peter the Great.

Photo 2. Densuș church, Hațeg County, has a roof made of stone plates. Photo: Alexandru Baboș, Creative Common Attribution.

Photo 2. Densuș church, Hațeg County, has a roof made of stone plates. Photo: Alexandru Baboș, Creative Common Attribution.

Romania is situated in the Northern hemisphere, about halfway between the Equator and the North Pole. The climate features hot, dry summers with temperatures that can rise to 113 degrees Fahrenheit in the South, and cold winters, with temperatures that can drop to minus 22 degrees in the depressions of Transylvania, with heavy snow and strong winds. There are some spots with milder temperatures, close to the sea and in the western part of the country.

Why all this introduction? Because specific geographic conditions lead to specific building systems. People living in areas with abundant rain and snow need materials and systems that resist and shed water; after all, the steeper the slope, the faster the water is evacuated off the roof.

Cultural influences color the patrimony, but climatic conditions define the geometry and the materials that are used for roofs. As there are different climatic conditions as well as diverse cultural influences, the building typologies of the roofs are, in their turn, diverse.

Ancient Settlements

Photo 3. Below-ground cottage in the Village Museum in Bucharest. Photo: Ana-Maria Dabija.

Photo 3. Below-ground cottage in the Village Museum in Bucharest. Photo: Ana-Maria Dabija.

Although these territories were inhabited for millennia, the roofs did not “travel” in time as long as the walls. The six ancient citadels of the Dacians, located almost in the center of Romania in the southwestern side of the Transylvanian highlands, still preserve ruins of the limestone, andesite or wooden columns of the shrines, altars, palaces and agoras. No roofs survived. (See Photo 1.) We can only presume that the materials that were used for the roofing were wood shingles or thatch, which would explain both why artefacts of the roofs could not be found and also why the deterioration is so advanced.

After Rome conquered Dacia, emperor Trajanus built a citadel that was supposed to represent continuity with the previous civilization: the Sarmizegetusa Ulpia Traiana. It seems to have had an active life, considering the temples, palaces and dwellings that we inherited, including an amphitheater for 5,000 people. Still, no roofing traces survived.

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Roof Rot: Ignorance Is an Easy Way to Damage Low-slope Residential Roofs

Change often brings with it unintended consequences, and the issue of reflective roof surfaces in North America is no exception. In the late 1990s, U.S. cities in northern climates started to mandate the use of reflective roof—more for politics, feel-good, pseudo-environmental reasons than sustainable, resilient and durable reasons. In my estimation, cool roofs often did more to lower the quality of buildings than enhance them. Furthermore, code and standard changes were made with no understanding of the result and no education to the architects of America.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Although the resulting unintended consequences affected commercial and residential buildings, it was the often-catastrophic results on low-slope residential buildings that went untold and left homeowners with tens of thousands of dollars of corrective work on basically new residences.

Following is a summary of how these concerns evolved in wood-framed residential construction. I’ve included case studies of failures, potential solutions and lessons learned.

HISTORY

During the industrialization of America’s large cities throughout the 1800s, the need for labor caused populations to explode. To house the labor migration, row houses (3- to 4-story structures, often with a garden level and four or more narrow units) were constructed approximately 3-feet apart, block after block, creating medium-sized apartment blocks. Most of these row houses were wood-framed, masonry veneer with low-slope roof structures. The interior walls and ceilings were finished in cementitious plaster, which provided a durable, fire-resistive finish. The plaster also performed as an effective air and vapor barrier, preventing interior conditioned air from penetrating into the non-insulated walls and ceilings where it could condense within the walls and roof on cold days.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Heating costs were low, so little—if any—insulation was installed in the walls and roof. Roofs were composed of built-up asphalt and coal tar, both smooth and aggregate surfaced. Attic spaces often 4 to 6 feet in height were vented via static vents. Any conditioned air that passed to the attic was able to dissipate through these static vents. This method of construction performed without significant attic condensation, and the roof systems and roof structure served these buildings for decades.

In the mid 1990s, researchers (theoretical researchers with no architectural, engineering, roofing, construction or practical building technology experience or knowledge) at research institutes conducted studies into the effects of minimizing solar gain through the roof via a reflective surface. Based on the researchers’ algorithmic findings and recommendations (regardless of their validity), environmental groups used the concept to promote change. Large cities started introducing new energy codes with reflective roofing requirements and prescribed reflectance values. These new codes contained greater insulation requirements, which was a benefit. However, in this one code adoption, roof systems, such as coal-tar pitch, that had performed for centuries were no longer permitted. Consequently, roofing contractors went out of business and so did some roofing material manufacturers because of unproven and suspect research.

Photos and Details: Hutchinson Design Group Ltd.

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