Ignorance, Lack of Foresight Can Lead to Roof Designs That Defy Common Sense

Photo 1: Really! This is ridiculous. A 24-inch curb should have been specified. Twelve-inch roof curbs in my opinion should be eliminated from manufacturing offerings and 16-inch curbs should become the new norm. Anyone listening here? IMAGES: HUTCHINSON DESIGN GROUP LTD.

As you know, I am not shy about calling out detailing that is not to the standard of care or construction that is not to the standard of workmanship. But this article is set aside for those special instances where those involved showed a great lack of intelligence or common sense. In other words, they were just plain stupid.

We are often requested to perform observation services on roof installations designed (and I use that term loosely) by others. Oh, what one can learn. It is impressive that some of the design firms are actually getting paid for the documents we see.

The following conditions and discussions border on the comical. The truth, though, is that they are sad realities, but at least they can function as a learning tool. Let this be the first step in providing better detailing.

Roof Hatches

After roof drains with the hole in the membrane cut out so small that you wonder if the drain takes any water, the condition the makes me shake my head the most is the roof hatch with a 12-inch curb set on multiple layers of wood blocking. (See Photo 1.) Sometimes I think it’s the architects’ nod to keep the carpenters’ union happy. More often than not, the reason this occurs is because the designer does not calculate the height of insulation (another violation of the standard of care) that would have buried the hatch.

Photo 2: When the carpenters’ union is supported and wood blocking used, it could at least match the size of the curb flange. The roofing contractor had to cut several layers of insulation to fit, resulting in various voids, which, you guessed it, were not filled with spray foam. Corrective work required was not so easy.

To make matters worse, the wood on the interior is exposed and creates the condition that can catch clothing. Wrapping the wood in sheet metal can alleviate this concern, which of course would require forethought and detail. Often the roof ladder ends up short because the height of the insulation is not accounted for, creating another safety condition.

In Photo 2 you can see that the wood blocking is not even the same width at the flange of the hatch, creating a condition in which the insulation may not be tight to the wood and curb. This all could have been eliminated if the designer had known the insulation height and specified a roof hatch with the appropriate curb height.

With the new insulation thermal values required by code, the old 12-inch curb heights, in my opinion, should be eliminated and 16-inch curbs should become the new standard. We specify 16-inch and 18-inch curb heights — with thermally broken curbs — as a matter of course. (See Figure 1.)

While we’re at it, let’s also talk about the roof hatch location. The role of the roof hatch is to provide safe roof access. Why, then, are they so often located at the roof edge? Often it’s so a ladder can be mounted on the exterior wall, but it just doesn’t make sense to step out of a roof hatch just feet — or even inches — from the roof edge. I do not care if there is a ladder up post and a safety rail — it’s not fun walking to a hatch 20 stories up with winds changing direction every few minutes. (See Photo 3.)

Figure 1: A properly detailed roof hatch. Specifying and detailing roof hatches with 16-inch, 18-inch or greater heights is the proper standard of care method. (Sorry, carpenters — no wood blocking needed.) The curb is also thermally broken and has greater insulation than normal. Note the 2-inch-thick rubber pavers that protect the roof insulation.

Let us not forget the protection of the roof cover. Too many roofs are designed and installed without a cover board. The membrane is directly on top of the insulation, which often has a low psi, and after a few years of foot traffic, this condition results in crushed insulation — even if walkway pads are used. (Some walkways are so thin they are almost worthless.) The result is failure of the bond with adhered roof systems and fastener penetration through the membrane with mechanically attached systems. Nothing like designing in failure. We, by the way, specify 2-inch-thick rubber pavers cut to fit.

Level Copings

Photo 3: Gee, let’s make it a bit more unsafe and turn the roof hatch around. Locating roof hatches along or near roof edges is just plain stupid.

Walking historic fortifications, castles, or fortress sites, did you ever wonder why the top of the walls, parapets, crenellations all have sloping stones? Empirical experience taught the builders that water running down the exterior walls was not good, so they sloped the battlements toward the interior. So, why do so many designers have flat copings and/or gravel stop edges? Several local schools are exhibiting the effects of water runoff from the level copings, including staining, moss, brick faces spalling off the brick, and mortar deterioration. (See Photos 4A and 4B.) Sloping copings back toward the interior helps move water and snow to the roof, preventing it from saturating brick and other façade materials. (See Photo 5.) This is a standard of care issue for designers.

Additionally, the coping is often installed on partially covered wood and most certainly underlying conditions where the membrane does not lap over the wood blocking onto the façade. This should be, in my opinion, a code requirement, along with sloping the copings back to the interior.

Lack of Coordination With Mechanical and Plumbing

Photo 4A: Taxpayer dollars at work: Flat copings above the walls on this school allow water to run down and saturate the masonry, resulting in severe deterioration. At the time of captioning this photo, the Chicago area has 18 inches of snow and portions of this wall are coated in ice.

Several years ago, I presented a paper at a Durability of Materials Conference on the need in new construction for coordination by the roof system designer with the HVAC and plumbing engineers. I argued that the same detail on the roofing sheets should also appear on the MEP sheets — the only difference being that the notes pertaining to the roofing be shown, but in a lower opacity. I am saddened that no one has read that paper. Pipe portals are one of the details that can turn my stomach. (See Photo 6.) They are seldom included on the roof drawings, and even if they are, common problems include penetrations through the roof deck that are never sealed; curbs that are never insulated; portals that are never sealed to the curb cap; and nipples that are never sealed or secured. Of course, the HVAC contractor often tries to place as many wires, pipes, and pieces of conduit as possible through one nipple and then “caulk the hell out of it.” In cold weather locations, condensation on the interior of the curb often occurs and drips into the interior creating — you got it —a “roof leak.”

Roof Drains

Photo 4B: Masonry walls that were expected to have a 40–50-year service life are deteriorating and will require substantial repair.

Selecting the correct roof drain, sump pan, extension — whether fixed or adjustable — and the type of drain dome should be a function of the roof designer and plumbing engineer working together. When you have 4 to 5 inches of insulation at the roof drain, an extension is required. The sump pan should be provided by and installed by the plumbing contractor, which results in the drain being flush with the top of the roof deck — not dropped 1.5 inches, as it is when the steel contractor installs the sump pan which is 40 years out of date. A reversible collar, an extension ring, and a cast iron dome should be specified and detailed. But there is often no coordination between the roof system designer and the plumbing engineer. The plumber shows up with just a drain, and the roofing contractor says, “I can’t sump down 4 inches.” The solution is to then set the roof drain up off the roof deck — really? More insidious is when the roof drain is actually designed to be up off the deck. This is absurd. (See Figure 2.) Have you ever tried to re-roof a building, installing a vapor retarder, and find the roof drains set up off the deck? (See Photo 7.) Not cool when it rains and the drains are high — just stupid.

Roof Access Door Sills

Photo 5: As can be seen on this photo, when the coping is properly sloped to the interior the snow, frost melt and rainwater slope onto the roof system and not onto the exterior wall.

Whether the access is for the roof, a rooftop deck, or roof patio, designers love to keep those sills as low as possible. (See Photo 8.) Then they do not detail appropriate transitions into the roof — no sill and jamb end dam waterproofing, no protective sill pans. I have one client in which the sliding glass doors on the second floor are over the first-floor interior, and the third-floor doors are over the second floor interior, and so on. This terraced design eases the height, but the leaks and the doors wreak havoc on the spaces below. Correcting the condition is not a cheap endeavor when you have to remove 12-foot sliders and transoms to install the correct waterproofing.

Is Stupid Taught?

Photo 6: I hate this type of detailing often specified by the mechanical engineer who has no clue. The curbs and/or spun aluminum portals are not insulated, the penetrations are never properly sealed, and more than one penetration is often passed through one nipple.

The conditions above are observed every week. Why do they occur? Most of the designers have little clue as to how to properly detail. There is little or no discussion in most universities on the building envelope and certainly on detailing. Thus, the graduate is forced to learn in the office from someone, and the person teaching them might have little knowledge themselves. I would have to say most architects don’t see the glory in roof system design. Way too many designs reference manufacturer details, which is a guide for detailing and a market-driven minimum to compete with other manufacturers doing the same. Contractors bid what’s on the drawing: “If it’s not shown, you’re not entitled to get it.” Many of the situations described in this article do not immediately create a concern, but the problems are latent. When the extent of the problem becomes clear, everyone has forgotten who installed the work and they call me to fix the problem. No learning takes place, and this is the true tragedy.

Figure 2: The wrong way to do it. Even today, some designers are showing the roof drains held up off the roof deck. The roofing crews, contractors, and plumbers who deal with these on roof replacement projects despise this type of detailing.
Photo 7: Roof drains set up off the deck make tying in the vapor retarder very difficult, and this is a nightmare for contractors during a re-roofing application. If a temporary roof/vapor retarder is installed and left without new roofing so that large areas of a roof can be removed, the drains are high and ponding water is a concern.
Photo 8: Having door interior floors (especially wood), doorsills and balcony or patio decks in relatively the same plane is asking for water entry. Most designers do not properly design the sill, which requires waterproofing the rough opening; sill pan with soldered end dams; and door frames and sill with proper weeping.

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

About the Author

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

1 Comment on "Ignorance, Lack of Foresight Can Lead to Roof Designs That Defy Common Sense"

  1. From what I have read, I agree that “incorrect” detailing is due to plain lack of common sense. 🙁 May this great article give insight to those working with design/detailing.

    Thanks for the insightful/comical, great read! I learned a lot.

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