When stripped down to its most fundamental purpose, architecture is about sheltering people from the elements. From this point of view, perhaps the most important part of any building is its roof. Roofs keep us dry and, combined with walls, warm. The sheltering function of a roof is a straightforward concept, yet a quick glance at statistics on building failures will show that—in spite of having a good handle on the idea of the roof—those in the architecture, engineering, and construction industries have a rather difficult time putting it into practice in acceptably reliable ways.
Roofs, on average, last only about half of their designed lifetime. Furthermore, 40 percent of all building-related problems are due to water intrusion—and water usually intrudes through roofs. Most startling, though, is the fact that, while roofs only make up about 2 percent of construction costs, water intrusion accounts for more than 70 percent of construction litigation; roof failures and related fallout are often at the root of the issue. So what’s going wrong?
Before architects start sweating under the collar too much, it must be said that the design side of the building industry is not considered the primary culprit. “The most common thing that leads to roof failures is improper installation,” says Stan Graveline, vice president of technical services at Sika Sarnafil, a global manufacturer of roofing and waterproofing systems. “The contractor doesn’t put the materials on properly and ultimately the roof begins to leak at a joint or seam.”
Karen L. Warseck, AIA, president of Building Diagnostics Associates (BDA), a Florida-based firm that specializes in identifying and fixing building-envelope problems, breaks it down further: “Normally we find that it’s about 60 to 70 percent construction, 20 to 25 percent design, and 10 percent materials,” she says. Her firm has experience to back up her claims. BDA has been involved in 1,500 remediation projects “from Alaska to the Bahamas,” Warseck says.
Architects do play a part in this blame game, and there are measures that they can take in the design phase to help prevent roof failure. After all, contractors follow construction documents prepared by architects, and if the CDs don’t include correct details, problems are bound to occur. What follows are common reasons why architects flub roof designs, and some ways they can improve their game.
Detailing in Three Dimensions
“What do architects do to make their buildings fail?” Warseck asks. “The biggest thing they do is they don’t consider things in three dimensions. It’s ironic because architects are supposed to be able to think in 3D. But when it comes to roof details, that three-dimensional thinking goes out the window.”
The conventional set of architectural drawings includes numerous sections. Eventually, though, those sections meet other sections and designers must figure out how the two will meet (i.e., how an edge condition should be flashed to prevent water intrusion). What happens all too often is that architects turn inadequate sectional drawings over to the contractors, who in turn leave it up to a roofing subcontractor to figure it out. In those cases, you wind up with a laborer faced with challenges that he or she is not prepared to overcome. The typical on-site solution to an ambiguous edge condition is to patch everything together with roofing cement and caulk. Since these materials are not designed to last as long or to have the same amount of durability as other roofing materials, it’s only a matter of time before the whole thing fails. And when it does, the lawyers wind up at the designer’s door looking for retribution.
“Roofs should last 20-plus years, but caulking and sealant only last a few years,” Graveline says. “If you rely on caulking rather than proper details, water begins to get in. You have to go back and re-caulk and re-caulk, when in fact there are more-permanent ways to flash things. But if … [roofs are] not detailed properly, people will go to the path of least resistance. A lot of times that’s using a lot of sealant.”
By and large, the industry relies on generic details such as those found in CAD. Most generic details are 2D sections, which may not be adequate to show how an item should be flashed; what works along the length of a wall or parapet doesn’t work at the ends. Wherever there is a transition, penetration, or termination, there must be a detail. Architects must be vigilant and detail all such trouble spots to make sure that they are properly flashed, and they need to review their drawings for impossible-to-flash details. As the industry transitions to BIM, the generic 3D details need to be checked just as, if not even more, carefully on a project-by-project basis.
Some details are more common trouble spots than others. “One of the most common things we see done wrong are expansion joints,” Warseck says. “Nobody bothers to detail what happens when an expansion joint ends. The roofer just runs it up to a wall and puts a glob of sealant on it, and of course it’s going to fail.” There are other trouble spots, such as curved parapets, stairs that terminate at the roof, unistruts, channels, interior gutters, doors, and louvers not set high enough above the roof line, and penetrations too close to walls and curbs. Infill projects and additions pose another set of problems. Even if they touch, the old and new buildings may move independently of one another and—if improperly detailed—the roofing materials over the joints may be prone to rippling or cracking as a result of this movement, allowing water to intrude.