About Thomas W. Hutchinson, AIA, FRCI, RRC, CSI, RRP

Thomas W. Hutchinson, AIA,FRCI, RRC, is principal of Hutchinson Design Group Ltd., Barrington, Ill., and a member of Roofing’s editorial advisory board.

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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Architects and Roof System Designers: Your Details and Drawings Are Seriously Lacking Design Intent

Dear Mr. and Ms. Architect and Roof System Designer:
The following are comments I hear over and over:

  • “Seventy-five percent of the time I cannot determine what roof assembly an architect wants from a spec.”
  • “One always feels they have to play private detective and try to figure out what [a roof system designer] actually wants.”

As an architect and registered roof consultant, I take great pride in my roof system designs and detailing, which are project specific, at minimum meet the code, and more often than not exceed code with all conditions and building components that impinge on the roof detailed for the specific project. In listening to construction managers, general contractors, roofing contractors and suppliers talk, you would think that architects barely know that the roof is on top of the building! It seems most do not even have basic knowledge and certainly don’t know when water may flow uphill. This is embarrassing to hear! It starts in the university with the curriculum placing all emphasis on building design and not how to actually construct a building. In many ways, this is good for my firm as we are busy fixing what should never have required fixing.

Peer review of several projects designed by very large (and what you would assume to be very sophisticated firms) and even small boutique firms reveals the following:

A. The roof system design is not code compliant in regard to tapered insulation.

B. The roof system itself is not code compliant, but contract documents require “contractor to verify or be responsible for code compliance”. This begs the question: Who is being paid to design? Is it the architect or the contractor?

C. Structural and, especially, structural lightweight concrete pose significant roofing challenges and architects have no clue about that, resulting in roof systems in danger of imminent failure.

D. The accuracy of construction documents in general is very, very low. Even I cannot often determine what roof assembly an architect wants from a specification.

  • 1. For example, architects do not list products in the specs that will be used in the assembly.
  • 2. Substrate boards, cover boards and vapor barriers are frequently listed in the specs but never shown on the plan.

E. The detailing of wall air barriers to roof vapor or air barriers is not shown and certainly no definition of responsibility prescribed as to who is to tie these materials together.

F. Understanding of material limitations is non-existent.

  • 1. Weather, wind, cold, snow, humidity and temperature affect the installation of roof system components. I especially get a kick out of seeing water-based adhesives being specified for construction taking place in winter; this means future work for my firm.

G. Roof edges and how they terminate at high walls is never detailed.

H. Roof drains and curbs are improperly or not detailed.

I. Specifications are inadequate—often boilerplate generic—and do not match the drawings. I’ve also seen non-specific details that are not to scale or do not reflect actual conditions.

  • 1. Design wind speed is not given when appropriate.
  • 2. Warranty requirements are in- correct, not thought-out or not specified at all.

J. Architects or consultants sometimes have multiple designs listed in the specification, leaving it to the con- tractor to issue RFIs that, more often than not, are not answered.

  • 1. These inconsistencies lead to frustration and, in many cases, the contractors just decide it is not worth the time or effort to even bid the project or add a good deal of money to cover undefined items.

K. I’ve witnessed owners who have hired professionals to design build- ings costing hundreds of millions of dollars, and yet these “professionals” often do not exhibit the standard of care expected.

  • 1. Poor designs compound when met with an irresponsible contractor who will not do his or her due diligence and investigate what is needed to install a quality system.

Illustrations: courtesy of Hutchinson Design Group Ltd.

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The Integration of Roof and Brick Requires Concise Details

PHOTO 1: The through-wall flashing stainless-steel drip can be observed projecting nicely from the wall—but the termination of the roof base flashing more than 1-inch below resulted in a section of the brick wall that allows water to pass into the wall below the through-wall flashing and behind the roof base flashing, resulting in the damage seen in Photo 2.

PHOTO 1: The through-wall flashing stainless-steel drip can be observed projecting nicely from the wall—but the termination of the roof base flashing more than 1-inch below resulted in a section of the brick wall that allows water to pass into the wall below the through-wall flashing and behind the roof base flashing, resulting in the damage seen in Photo 2.

Projects are perceived to be successful by their ability to prevent disturbance from weather, including rain. Have you ever heard two architects talking about Frank Lloyd Wright?

“What a genius! His spatial conception is magnificent, even after 100 years.”

“But all his buildings leak!”

I used to give a talk to University of Illinois architecture students in which I told them the quickest way to go out of business is to be sued. The quickest way to be sued is to have a building allow moisture intrusion. If he were alive today, Frank Lloyd Wright—God rest his soul—would be in jail (and a few current architects may be well on their way). Owners are not very kind when their “babies” leak.

Many roof termination interfaces are never even thought about by designers and are left to the roofing contractor to work out. This is not a recommended practice. One such condition—that every architect should be able to detail—is how the roof base flashing terminates at a masonry wall that has through-wall flashing and weeps at the base of the wall above the roof. I believe so fervently that architects should be proficient in detailing these conditions that I believe it should be required to procure their license.

WHY THE IMPORTANCE

The interface of roof base flashing and masonry through-wall systems occurs on a majority of commercial construction projects. If this transition is not performed correctly, moisture intrusion behind the roof base flashing to the interior will occur (see Photo 2). When this occurs, besides angering owners, it befuddles the architect. Photo 1 (left) shows a nice through-wall flashing drip extended out from the wall, weeps and roofing terminated with a termination bar and sealant. What could be wrong?

PHOTO 2: Moisture intrusion at the base of this wall was the result of water circumventing the through-wall flashing and roof base flashing termination seen in Photo 1. A big concern with conditions, such as this, is the propensity of the materials to promote mold growth.

PHOTO 2: Moisture intrusion at the base of this wall was the result of water circumventing the through-wall flashing
and roof base flashing termination seen in Photo 1. A big concern with conditions, such as this, is the propensity of the materials to promote mold growth.

The exposed brick above the termination bar and below the stain- less-steel drip of the through-wall flashing is susceptible to water flowing down the surface of the brick. Water passing through the brick above is supposed to be weeped out; however, at the exposed brick above the termination bar, the water moves into the wall and has nowhere to go but inward.

The cost to repair these conditions can be, depending on the conditions, expensive. Repairs often require brick removal and through-wall flashing mitigation. In this particular case, be- cause there is a stainless-steel drip, my team recommended a stainless-steel counterflashing be pop-riveted to the drip and extended over the termination bar.

CHALLENGES

Why is the interface of roof base flashing and masonry through-wall systems so difficult for architects and roof consultants to detail? I believe it is because they have no clue it needs to be detailed as an interface, especially because detailing of appropriate through-wall systems is so sporadic. I endeavor in this article to change at least the knowledge part.

The detailing of this condition not only requires the ability to interface two building systems, but also requires considerable time to ensure specification of wall sectional details and roofing details are appropriately placed where the responsible trades will see them.

PHOTO 3: Still under construction, the stainless-steel counterflashing has been installed. The roof base flashing will terminate below the stainless-steel counterflashing receiver. Hutch prefers brick below the through-wall flashing and above the roof deck, though the masonry mortar joints below the through-wall flashing should have been struck flush.

PHOTO 3: Still under construction, the stainless-steel counterflashing has
been installed. The roof base flashing will terminate below the stainless-steel counterflashing receiver. Hutch prefers brick below the through-wall flashing and above the roof deck, though the masonry mortar joints below the through-wall flashing should have been struck flush.

NEW CONSTRUCTION

New construction provides us a clean slate to “do it right the first time”. The first order of business is to determine the height of the base flashing. This can be tricky with tapered insulation and slope structures with saddles. Let’s consider the following examples (see Detail 4, page 3):

EXAMPLE 1
We are dealing with a flat roof, tapered insulation, cover board and bead-foam insulation in ASHRAE Climate Zone 5, which has an R-30 minimum.

  • The roof drain is 32-feet away from the wall. Code requires 5.2 inches of insulation at 4 feet from the drain, so let’s assume 5 inches at the drain.
  • 1/4-inch tapered starts at 1/2 inch at 32 feet. That’s 8 inches, plus the starting thickness of 1/2 inch, which equals 8 1/2 inches.
  • Cover-board thickness is 1/2 inch.
  • Bead foam thickness is 3/16 inch for each layer. Let’s assume five layers, so 1 foot of bead foam.
  • Thus, the surface of the roof at the wall will be 15 inches above the roof deck.

Because you would like to work at the masonry coursing level and given that concrete masonry units (CMU) are nominal 8 inches, you are looking at placing the through-wall flashing 24 inches above the roof deck.

This 24-inch dimension of where to place the through-wall flashing needs to be placed on the building section and/or wall section because the mason, which will be onsite prior to the roofing contractor, will need to know this information.

This 24-inch height begs another termination question: What occurs at the roof edge with this height? Hold that thought for now. Terminations at intersections will be discussed in future articles.

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Code-mandated Thermal Insulation Thicknesses Require Raising Roof Access Door and Clerestory Sill Details

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

The most common concern I hear related to increasing insulation thickness (a result of increased thermal values of tapered insulation), especially in regard to roofing removal and replacement, is, “OMG! What about the roof access door and/or clerestory?” You can also include, for those knowledgeable enough to consider it, existing through-wall flashing systems and weeps.

I’m a bit taken aback by this concern; I have been dealing with roof access doors and clerestory sills for the past 30 years and, for the most part, have had no problems. My first thought is that roof system designers are now being forced to take these conditions seriously. This is a big deal! They just have no clue.

In the next few pages, I’ll review several possible solutions to these dilemmas, provide some detailing suggestions and give you, the designer, some confidence to make these design and detailing solutions. For the purpose of this article, I will assume reroofing scenarios where the challenge is the greatest because the conditions requiring modification are existing.

THE ACCESS DOOR

For many and perhaps most contractors who sell and, dare I say, design roofs, it is the perceived “large” expense of modifying existing conditions that is most daunting. Often, these conditions are not recognized until the door sill is several inches below the new roof sur- face. Not a good predicament. Planning for and incorporating such details into the roof system design will go a long way to minimizing costs, easing coordination and bringing less tension to a project.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

Door access to the roof is the easiest method to access a roof. These doors are typically off a stair tower or mechanical penthouse and most often less than 12 inches above the existing roof as foresight was not often provided (see photos 1, 2 and 6 through 9). With tapered insulation thickness easily exceeding 12 inches, one can see that door sills can be issues with new roof systems and need to be considered.

Designers should first assess the condition of the door and frame, typically hollow metal. Doors and frames that are heavily rusted should not be modified and reused, but discarded, and new ones should be specified. The hardware too needs to be assessed: Are the hinges free of corrosion and distortion? Is the closure still in use or detached and hanging off the door frame? The condition of door sweeps, knobs, lockset and weather stripping should also be determined. Ninety-nine percent of the time it is prudent to replace these parts.

As the roof system design develops, the designer should start to get a feel for the thickness of insulation at the door. It is very important the designer also consider the thicknesses that vapor retarders, bead and spray-foam adhesives, cover and board and protective pavers will add. These can easily be an additional 4 inches.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

Once the sill height is determined, the design of the sill, door and frame can commence. If the sill height to be raised is small—1 1/2 to 3 inches—it can often be raised with wood blocking cut to fit the hollow metal frame, flashed with the roofing membrane, metal sill flashing and a new door threshold installed, and the door and frame painted. This will, of course, require the removal of the existing threshold and door which will need to be cut down to fit and then bottom-sealed with a new metal closure (see details A and B, page 3).

When the door sill needs to be raised above 3 inches, the design and door considerations increase. Let’s consider that the door and frame is set into a masonry wall of face brick with CMU backup. Although most hollow metal doors are 7 feet 2 inches to match masonry coursing, after the modification the door may be shorter. For example, if a door is 7 feet 2 inches and you must raise the sill 5 inches, the new door and frame will need to be 6 foot 9 inches.
PHOTOS & ILLUSTRATIONS: Hutchinson Design Group Ltd.

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Concise Details and Coordination between Trades Will Lead to a Quality Long-term Solution for Roof Drains

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

The 2015 IECC roof thermal insulation codes have forced roof system designers to actually think through the roof system design rather than rely on generic manufacturers’ details or the old built-up roof detail that has been used in the office. Don’t laugh! I see it all the time. For the purpose of this article, I will deal with new construction so I can address the coordination of the interrelated disciplines: plumbing, steel and roof design. In roofing removal and replacement projects, the process and design elements would be similar but the existing roof deck and structural framing would be in place. The existing roof drain would need to be evaluated as to whether it could remain or needs to be replaced. My firm typically replaces 85 percent of all old roof drains for a variety of reasons.

The new 2015 IECC has made two distinctive changes to the 2012 IECC in regard to the thermal insulation requirements for low-slope roofs with the continuous insulation on the exterior side of the roof deck:

  • 1. It increased the minimum requirement of thermal R-value in each of the ASHRAE regions.
  • 2. It now requires that this minimum R-value be attained within 4 feet of the roof drain.

Item two is the game changer. If you consider that with tapered insulation you now need to meet the minimum near the drain, as opposed to an aver- age, the total insulation thickness can increase substantially.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

THE ROOF DRAIN CHALLENGE

The challenge I see for designers is how to properly achieve a roof system design that will accommodate the new insulation thicknesses (without holding the drain off the roof deck, which I believe is below the designer’s standard of care), transition the roof membrane into the drain and coordinate with the related disciplines.

For the purpose of this tutorial, let’s make the following assumptions:

  • Steel roof deck, level, no slope
  • Internal roof drains
  • Vapor/air retarder required, placed on sheathing
  • Base layer and tapered insulation will be required
  • Cover board
  • Fully adhered 60-mil EPDM
  • ASHRAE Zone 5: Chicago area

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

Once the roof drain locations have been selected (for those new to this, the roof system designer should select the roof drain locations to best suit the tapered insulation layout), one should try to locate the roof drain in linear alignment to reduce tapered insulation offsets. The drain outlets should be of good size, 4-inch minimum, even if the plumbing engineer says they can be smaller. Don’t place them hundreds of feet apart. Once the roof drain location is selected, inform the plumbing and structural engineers.

STRUCTURAL ENGINEER COORDINATION
The first order of business would be to give the structural engineer a call and tell him the plumbing engineer will specify the roof drain sump pan and that the structural engineer should not specify an archaic, out-of-date sump pan for built-up roofs incorporating minimal insulation.

When located in the field of the roof, the roof drains should be at structural mid spans, not at columns. When a structural roof slope is used and sloped to an exterior roof edge, the roof drains should be located as close to walls as possible. Do not locate drains sever- al or more feet off the roof edge; it is just too difficult to back slope to them. Inform the structural engineer that the steel angles used to frame the opening need to be coped to the structure, not laid atop the structure. There’s no need to raise the roof deck right where all the water is to drain.

FIGURE 2: A threaded roof drain extension is required to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

FIGURE 2: A threaded roof drain extension is required
to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

PLUMBING COORDINATION
Now call the plumbing engineer and tell him you need a metal sump receiver (see Photo 1), underdeck clamp (see Photo 2), cast-iron roof drain with reversible collar, threaded extension ring capable of expanding upward 5 inches, and cast-iron roof drain clamping ring and dome.

Send the structural and plumbing engineer your schematic roof drain detail so they know exactly what you are thinking. Then suggest they place your detail on their drawings. Why? Because you cannot believe how much the plumbing roof-related details and architectural roof details often differ! Because details differ, the trade that works on the project first—plumbing— leaves the roofing contractor to deal with any inconsistencies.

Your detail at this point should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck (see Figure 1).

PHOTOS AND ILLUSTRATIONS: HUTCHINSON DESIGN GROUP LLC

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Increased Thermal Values Affect an Existing Roof Edge

Recent code and standard development has resulted in increased thermal insulation. This increase has required greater and greater insulation thicknesses, which are even thicker when
tapered insulation is added. This roof system thickness, especially in reroofing design, has thrown a curveball to many designers: How should they address existing rooftop conditions?

On a recent project in which the roof sustained a wind event, investigation for the design of the new roof edge and system found multiple concerns: open metal stud cavities to the parapet, open metal panel joints, wood and substrate boards attached with drywall wall screws and moisture drive concerns. This information led to the design of one of the author’s most complicated roof edges.

Photo 1: On a recent project in which the roof sustained a wind event, investigation for the design of the new roof edge and system found multiple concerns: open metal stud cavities to the parapet, open metal panel joints, wood and substrate boards attached with drywall wall screws and moisture drive concerns. This information led to the design of one of the author’s most complicated roof edges (see Figure 1).

I have successfully dealt with this for more than three decades and mostly with ease. However, based on the fight being put up by the Chicago Roofing Contractors Association (CRCA), you would think it is putting contractors out of business rather than having the potential to increase their bottom lines.

Consequently, this will be the first of several articles discussing how designers can deal with existing conditions on the roof when increased thermal values are required. This article will explain the roof edge—the first defense against wind uplift and often an aesthetic concern. Future topics will include drains, roof curbs, access doors, windows, RTUs and plumbing vents.

WHY THE NEED

Twenty-five or 30 years ago, insulation was what you placed on the roof deck to act as a separator between the roof cover and roof deck, especially with the increased use of fluted steel decks instead of monolithic-type decks, like concrete, gypsum, wood and cementitious wood fiber. Prior to that, roof covers were often placed directly on these monolithic roof decks sans insulation.

On a recent project in which the roof sustained a wind event, investigation for the design of the new roof edge and system found multiple concerns: open metal stud cavities to the parapet, open metal panel joints, wood and substrate boards attached with drywall wall screws and moisture drive concerns. This information led to the design of one of the author’s most complicated roof edges.

Figure 1: On a recent project in which the roof sustained a wind event, investigation for the design of the new roof edge and system found multiple concerns: open metal stud cavities to the parapet, open metal panel joints, wood and substrate boards attached with drywall wall screws and moisture drive concerns. This information led to the design of one of the author’s most complicated roof edges (see Photo 1).

It has only been within the last 25 to 30 years that insulation has become an integral component of the roof system, often changing how the roof cover behaved. As energy and the conservation of energy became vogue, codes and standards became more stringent in regard to thermal insulation values. With the increase in R-value came an increase in the thickness of insulation. This in turn requires roof edges be higher to accommodate the increases in insulation, ultimately changing how the roof edge on buildings without parapets are designed.

Stacking wood to raise the roof edge is old school. Here you can see the new wood blocking is the second stacking over previously installed wood on a previous reroof.

Photo 2: Stacking wood to raise the roof edge is old school. Here you can see the new wood blocking is the second stacking over previously installed wood on a previous reroof.

The use of tapered insulation with thicknesses often above 12 inches changed how the roof edge is treated, especially in reroofing situations, which has resulted in design challenges. Add to this, modern building design that forewent parapets for gravel stop; the challenge of raising the roof edge to accommodate new insulation heights has dramatically increased.

The Washington, D.C.-based American Institute of Architects has issued a challenge to the design community to make all new construction Zero Energy Buildings (buildings that produce as much energy as they use) by 2030. Intuitively, more insulation (and perhaps fewer windows) will result in a building that uses less energy and, thus, more easily achieves a balance point.

To strengthen the multiple stacks of 2xs, 3/4-inch plywood is being added on the exterior.

Photo 3: To strengthen the multiple stacks of 2xs, 3/4-inch plywood is being added on the exterior.

This altruistic, far-reaching goal is being fought. CRCA, for example, is fighting the new code increases in roof insulation. Although the organization states a variety of reasons, it appears that the fear of owners delaying work that costs more because of increased insulation thickness is the greatest concern. This is interesting because design—by state mandate—is the purvey of licensed design professionals. Is the CRCA advocating design by non-licensed designers? I believe the CRCA’s position is foolish. Why would a predominately union-based contractor organization fight a code mandate that allows their members to increase profits? Perhaps the challenge by “right to work contractors” is greater than believed.

CONCERNS: LEGITIMATE OR NOT

There are a number of concerns, or design challenges, as I like to say, to raising the roof edge. For us architects, respecting the architect’s vision and design intent is often in conflict with what may need to be accomplished. I have worked with clients in buildings of note, designed by well-known architects, and have been able to respect every detail of the roof-edge vision. It is very difficult and challenging.

When stacking, wood joints should be offset and scarfed at 45 degrees.

Photo 4: When stacking, wood joints should be offset and scarfed at 45 degrees.

Another concern can be cost. Historically, a dimensional 2x was set at the roof edge and nailed; now we often raise the roof edge with prefabricated insulated curbs. Costs are always a concern but when budgeted correctly and the client is informed during the process, the project has always been realized within a year or two.

Another concern I often hear voiced is, “It’s difficult” or “I cannot figure it out”. When one considers that the roof edge must be (let’s say should be) tied to the building structure to resist wind loads, these are true concerns. These types of conditions often call on years of experience. Therefore, I say the challenge is on!

On this detail from an older project, the roof edge is being raised with multiple layers of 2 by 12s—a bit old school but easily performed. It is recommended to not specify preservative- treated wood, coated screws and off-set joints.

Figure 2: On this detail from an older project, the roof edge is being raised with multiple layers of 2 by 12s—a bit old school but easily performed. It is recommended to not specify preservative- treated wood, coated screws and off-set joints.

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With Today’s ‘New Age’ Roofs, Removing All System Components May Not Always Be Required or in the Clients’ Best Interest

Years ago, reroofing design involved removing all roof-system components down to the roof deck and rebuilding a new roof system up from there.

PHOTO 1: This EPDM roof’s service has been extended for nine years and counting, approaching 30 years in-situ performance. Here, the restoration of perimeter gravel- stop flashing and lap seams, as well as detailing of roof drains, penetrations and roof curbs, is nearing completion.

PHOTO 1: This EPDM roof’s service has been extended for nine years and counting, approaching 30 years in-situ performance. Here, the restoration of perimeter gravel- stop flashing and lap seams, as well as detailing of roof drains, penetrations and roof curbs, is nearing completion.

Although that is still a viable option and often performed, the coming of age of many single-membrane roofs has altered the method of installing a new reroof system. Options now include EPDM roof restoration; removal of the roof membrane and the addition of new insulation and roof membrane; using the existing roof membrane as a vapor retarder and adding new insulation and roof membrane; removal of the roof cover and installation of new, leaving all the existing insulation in place.

When I first moved into roof-system replacement design some 35 years ago, the dominant roof systems being removed were bituminous, specifically gravel-surfaced asphaltic and coal- tar-pitch built-up roofs. As they aged, their surfaces often started to blister, crack and undulate with ridges—surfaces often unsuitable for roof recover. The bitumen often was deteriorating because of ultraviolet-light exposure; when that occurred, the deterioration of the felts was not far behind. The insulation was mostly perlite or high-density wood fiber; the amount was minimal (low thermal value) and, more often than not, flat or with very minimal slope. Drains were erratically placed, tapered insulation was not often the case and roof edges were predominately gravel stops. In the Midwest, many roof decks were cementitious wood fiber. The roof covers were often patched again and again, even as water infiltrated the system.

PHOTO 2: The re-flashing of roof curbs is an integral part of the restoration of EPDM roof membranes.

PHOTO 2: The re-flashing of roof curbs is an integral part of the restoration of EPDM roof membranes.

When replacement was necessary, the roof-edge sheet metal was removed; the entire existing roof system was removed down to the roof deck; and a new roof system was designed, often incorporating vapor retarders/temporary roofs so the removal of multiple layers of roofing could be accomplished, roof curbs raised, and enhancements of roof drains, curbs and roof edge could occur prior to the installation of the new roof cover. Tapered insulation designs be- came common; this would often require realignment of the roof drains to simplify the tapered design and installation. To accommodate the new insulation thickness, the roof edge had to be raised as did roof curbs, RTU curbs, plumbing vents and roof drains via extensions. Roof membranes changed from bituminous to those classified as “single plies”: EPDM, PVC, CPE, CSPE.

These new roof-system replacement designs resulted in superior roofs—85 percent of all the reroofs I have designed are still in place, still performing, still saving the owner money. Life cycles have moved from eight to 12 years, up to 18 to 25 years and longer. They certainly were more expensive than the original installation and, if a roof designer didn’t have a handle on costs to provide the owner with estimated costs of construction, were often shocking. But these roof systems were good for the client, economy, environment and public.

PHOTO 3: When restoring EPDM roof membranes, the removal of roof penetration flashings and installation of new with target patches will provide another 20 years of watertight protection.

PHOTO 3: When restoring EPDM roof membranes, the removal of roof penetration flashings and installation of new with target patches will provide another 20 years of watertight protection.

Over the years, codes and standards have changed, especially in the past decade, requiring increased insulation values and roof-edge sheet-metal compliance with greater attention to wind-uplift resistance. As the new millennium arrived, these “new age” roofs came of age and owners started to look at their replacement—often with increased costs stifling their budgets.

LEAN THINKING

A factor that increased the performance of many roof systems in the past 20 years was the emergence and growth of the professional roof consultant, often degreed in architecture or engineering, educated in roofing, tested and certified. These professionals brought a scientific approach to roof-system design. Raleigh, N.C.-based RCI Inc. (formerly Roof Consultants Institute) was the conduit for this increased level of knowledge, professionalism and the growth in quality roof-system design and installation.

PHOTO 4: On this roof, the existing loose-laid membrane was removed, open insulation joints filled with spray-foam insulation and new insulation added to meet current code requirements. A new 90-mil EPDM membrane was installed and existing ballast moved onto it to 10-pounds-per-square-foot coverage.

PHOTO 4: On this roof, the existing loose-laid membrane was removed, open insulation joints filled with spray-foam insulation and new insulation added to meet current code requirements. A new 90-mil EPDM membrane was installed and existing ballast moved onto it to 10-pounds-per-square-foot coverage.

As these professionals started to examine the older “new age” roofs, those whose first responsibility was doing what was best for the client saw greater opportunity than just a costly full-roof replacement. Although many roofs today still need to be fully removed, prudent professionals see other opportunities, such as the following:

ROOF RESTORATION
EPDM membrane ages with little change in physical characteristics as opposed to its built-up roofing predecessor; therefore, EPDM membranes often can be “restored” in lieu of removing and replacing the roof. (Studies to support the lack of change in EPDM’s physical characteristics while it ages include Gish, 1992; Trial, 2004; and ERA, 2010.)

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The Roof Cover: The Cap on the Roof System

For nearly two years in this magazine, I have been discussing the various components that make up a roof system: roof deck, substrate boards, vapor/air retarder, insulation and cover boards (see “More from Hutch”, page 3). Although each component delivers its own unique benefit to the system, they are intended to work together. When designing a roofing system, components cannot be evaluated solely on their own and consideration must be taken for a holistic view of the system; all components must work together synergistically for sustainable performance. Unfortunately, I often have seen that when components are not designed to work within the system unintended consequences occur, such as a premature roof system failure. A roof system’s strength is only as good as its weakest link. The roof cover is the last component in the design of a durable, sustainable roof system—defined previously as being of long-term performance, which is the essence of sustainability.

This ballasted 90-mil EPDM roof was designed for 50 years of service life. All the roof-system components were designed to complement each other. The author has designed numerous ballasted EPDM roofs that are still in place providing service.

PHOTO 1: This ballasted 90-mil EPDM roof was designed for 50 years of service life. All the roof-system components
were designed to complement each other. The author has designed numerous ballasted EPDM roofs that are still in place providing service.

The roof cover for this article is defined as the waterproofing membrane outboard of the roof deck and all other roof-system components. It protects the system components from the effects of climate, rooftop use, foot traffic, bird and insect infestation, and animal husbandry. Without it, there is no roof, no protection and no safety. When mankind moved from cave dwellings to the open, the first thing early humans learned to construct was basic roof-cover protection. Thus, roof covers have been in existence since man’s earliest built environment.

WHAT CONSTITUTES AN APPROPRIATE ROOF COVER?

There is no one roof cover that is appropriate for all conditions and climates. It cannot be codified or prescribed, as many are trying to do, and cannot be randomly selected. I, and numerous other consultants, earn a good living investigating roof failures that result from inappropriate roof-cover and system component selection.

There are several criteria for roof-cover selection, such as:

  • Compatibility with selected adhesives and the substrate below.
  • Climate and geographic factors: seacoast, open plains, hills, mountains, snow, ice, hail, rainfall intensity, as well as micro-climates.
  • Compatibility with the effluent coming out of rooftop exhausts.
  • Local building-code requirements, such as R-value, fire and wind requirements.
  • Local contractors knowledgeable and experienced in its installation.
  • Roof use: Will it be just a roof or have some other use, such as supporting daily foot traffic to examine ammonia lines or have fork lifts driven over it?
  • Building geometry: Can the selected roof cover be installed with success or does the building’s configuration work against you?
  • Building occupancy, relative humidity, interior temperature management, building envelope system, interior building pressure management.
  • Building structural systems that support the enclosure.
  • Interfaces with the adjacent building systems.
  • Environmental, energy conservation and related local code/jurisdictional factors.
  • Delivering on the expectations of the building owner: Is it a LEED building? Does he/she want to go above and beyond roof insulation thermal-value requirements to achieve even better energy savings? Is he/she going to sell the building in the near future?

ROOF-COVER TYPES

There are many types of roof-cover options for the designer. Wood, stone, asphalt, tile, metal, reed, thatch, skins, mud and concrete are all roof covers used around the world in steep-slope applications. This article will examine the low-slope materials.

The dominant roof covers in the low-slope roof market are:

    Thermoset: EPDM

  • Roof sheets joined via tape and adhesive
  • Installed: mechanically fastened, fully adhered or ballasted
  • Thermoplastic: TPO or PVC

  • Roof sheets joined via heat welding
  • Installed: mechanically fastened, fully adhered or plate-bonded (often referred to as the “RhinoBond System”)
  • Asphaltic: modified bitumen

  • Installed in hot asphalt, cold adhesive or torch application
  • EPDM (ETHYLENE PROPYLENE DIENE MONOMER)

    Fully adhered EPDM on this high school in the Chicago suburbs is placed over a cover board, which provides a high degree of protection from hail and foot traffic.

    PHOTO 2: Fully adhered EPDM on this high school in the Chicago suburbs is placed over a cover board, which provides a high degree of protection from hail and foot traffic.


    EPDM is produced in three thicknesses— 45, 60 and 90 mil—with and without reinforcing. It can be procured with a fleece backing in traditional black or with a white laminate on top. The lap seams are typically bonded with seam tape and primer.

    EPDM has a 40-year history of performance; I have 30-year-old EPDM roof systems that I have designed that are still in place and still performing. Available in large sheets—up to 50-feet wide and 200-feet long—with factory-applied seam tape, installation can be very efficient. Fleece-back membrane and 90-mil product have superior hail and puncture resistance. Historical concerns with EPDM lap-seam failure revolved around liquid- applied splice adhesive; with seam tape technology this concern is virtually moot. Non-reinforced ballasted and mechanically fastened EPDM roof membrane can be recycled.

    EPDM can be installed as a ballasted, mechanically fastened or fully adhered system (see photos 1, 2 and 3). In my opinion, ballasted systems offer the greatest sustainability and energy-conservation potential. The majority of systems being installed today are fully adhered. Ballast lost its popularity when wind codes raised the concern of ballast coming off the roof in high-wind events. However, Clinton, Ohio-based RICOWI has observed through inspection that ballasted roofs performed well even in hurricane-prone locations when properly designed (see ANSI-SPRI RP4).

    PHOTOS: HUTCHINSON DESIGN GROUP LTD

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Cover Boards: The Membrane and Insulation Protector

Continuing on our roof system component analysis—after discussion of the roof deck, substrate board, vapor retarders and insulation—we now have worked our way up to the cover board. For the purpose of this discussion, the cover board is defined as the board placed upon the insulation as the final substrate to which the roof cover will be placed.

The purpose of the cover board is multifaceted; it can include:

    Insulation Protection: Placed to protect the thermal layer from the often deleterious effects of repeated foot traffic, which can result in insulation crushing, loss of roof-cover adhesive, inability to resist wind uplift and mechanical- fastener puncture through the membrane.

    Asphaltic core boards are very flexible and will conform to irregular surfaces and offsets without fracture. Here crews work to install the cover board in bead-foam adhesive in preparation for the three-ply modified bitumen roof cover. PHOTO: Clark Roofing

    Asphaltic core boards are very flexible and will conform to irregular
    surfaces and offsets without fracture. Here crews work to install the cover board in bead-foam adhesive in preparation for the three-ply modified bitumen roof cover. PHOTO: Clark Roofing

    Enhanced Roof-cover Adhesion: Cover boards can enhance the bond between the roof cover to the substrate.

    Enhanced Resistance to Wind Uplift: Cover boards and their ability to enhance the bond of the roof cover to the underlying substrate can result in an increased wind-uplift rating above and beyond that which can be provided with organic-faced insulations. They reduce the possible effects of facer-sheet delamination.

    Enhanced Fire Resistance: Many cover boards will enhance the fire resistance of the assembly.

    Hail Protection: Numerous studies show the value of cover boards in enhancing a roof cover’s ability to resist damage by hail.

    Provides Separation: A cover board provides separation between a roof cover and insulation that may not be compatible or the attachment adhesive of the roof membrane is not compatible with the insulation.

    Reduces Thermal Shorts (Energy Loss): Thermal insulation is often attached to the roof deck with mechanical fasteners, which results in conductive heat loss, up to 7 percent according to the Rosemont, Ill.-based National Roofing Contractors Association. This is a large value when some roof covers, which utilize mechanical attachment, purport to provide energy savings. Furthermore, when only one layer of insulation is used (a cardinal sin in my opinion) an additional 7 to 8 percent energy loss can occur. Placing a cover board above mechanically attached insulation and/or a single layer of insulation will enhance the energy performance of the roof system.

    Enhanced Roof-system Performance: I firmly believe the use of a roof cover board in a roof system improves the overall performance of the roof system and increases the probability of the roof attaining a long-term service life, which is the essence of sustainability. NRCA agrees; the organization recommends the use of cover boards in all low-slope assemblies.

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An ERA Study Proves EPDM Easily Lasts More than 30 Years

More and more building owners are seeing the light: Roof systems based on historical in situ performance for more than 30 years are the best roof system choice to benefit the environment. EPDM roof membrane has been utilized as a roof cover for more than 40 years, and there are numerous examples of ballasted roofs greater than 30-years old still performing. New seaming technologies, thicker membrane and enhanced design are creating roof systems with projected 50-year service lives. EPDM roof covers’ physical characteristics have changed little in 30 years, and because potential for 50-year-plus service life is possible, they are a solid choice of design professionals, building owners and school district representatives who truly desire a roof system that benefits the environment.

PHOTO 1: This ballasted 45-mil EPDM roof system has been in service for 32 years.

PHOTO 1: This ballasted 45-mil EPDM roof system has been in service for 32
years.

In 2010, the Washington, D.C.-based EPDM Roofing Association (ERA) was determined to answer the question: “How long can an EPDM roof perform?” Consequently, roof membrane samples from five roof systems with a minimum age of 30 years were obtained for testing of their physical properties. The physical and mechanical properties evaluated (using relevant ASTM standards) were overall thickness, tear resistance, tensile set, tensile strength and elongation, and water absorption. The results were positive, showing that even after 30 years of infield exposure nearly all the physical characteristics of EPDM membrane meet or exceed ASTM minimums. But the question of how long EPDM roofs could last remained. Thus, a second phase of testing was undertaken.

These properties were studied for “as received” and “after heat-conditioning” for up to 1,500 hours at 240 F. Results showing how these membranes performed before and after heat-conditioning are presented with the intent of defining characteristics for long-term service life of roof membranes.

TESTING PHASE ONE

Ethylene-propylene-diene terpolymer (EPDM) has been used in waterproofing and roof applications for more than 45 years in North America. Introduced into the roofing market in the 1960s, EPDM grew, especially after the 1970s oil embargo, to be a roofing membrane choice for new construction and roofing replacement projects. EPDM has achieved long-term in situ performance in part because of its chemical structure, mostly carbon black, which resists ozone and material decomposition, as well as degradation caused by UV light, which is the No. 1 degradation element to roofing materials exposed to the sun (see photo 1). The carbon black also provides reinforcement, yielding improved physical and mechanical properties.

Long-term performance of roof-cover material is dependent upon its resistance to the combined effects of ponding water, UV radiation, ozone, heat and thermal cycling. Geographical location can exacerbate or reduce the impact of climatic factors. In ballasted systems, the ballast acts to provide protection from the UV rays and minimizes the effect of climatic influences.

ERA’s study had three specific goals:

    1. Verify the long-term performance characteristics of EPDM membranes over 30 years. (At the time of the study, the only in situ membranes that were around for 30 years were 45-mil EPDM membranes. Currently 60- and 90-mil are the standard choices. It is assumed that results for the 45-mil material can be prorated for the thicker membrane.)

    2. Scientifically validate the empirical sustainability experiences.

    PHOTO 2: This recently installed, ballasted, 90-mil EPDM roof was designed for a 50-year service life.

    PHOTO 2: This recently installed, ballasted, 90-mil EPDM roof was designed for a 50-year service life.

    3. Create a foundation for specifier-to-owner discussions in regard to long-term service life. Five roofs, four ballasted and one fully adhered, with in situ service lives approaching or over 30 years were identified and samples were taken. All roofs were fully performing without moisture intrusion.

The samples were sent for testing per ASTM D4637 for:

  • Elongation
  • Tensile strength
  • Thickness
  • Factory seam strength (psi)

PHOTOS: HUTCHINSON DESIGN GROUP LTD.

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