March 24, 2005
Finding closure on building enclosures
By ROBERT BOMBINO
RDH Building Sciences
The building enclosure, or envelope, continues to be the topic of much discussion in the building industry. Premature deterioration of the building enclosure, mostly the result of water leakage around walls and windows, continues to be the source of tremendous economic loss and headaches for building owners, contractors, designers and others involved in the building process.
One only has to look at Vancouver, B.C., for an example of how building enclosure failures of epidemic proportions in the late 1980s and 90s resulted in much economic loss, mostly on the part of condo owners. The Vancouver experience fostered a complete loss of confidence in multi-unit residential construction.
But the problem isn't just north of the border; look around Seattle and you see many buildings wrapped in tarps undergoing exterior rehabilitation.
As a result of the widespread failures in Vancouver and Seattle, more attention is being paid to the building enclosure. Owners, developers, contractors, architects and attorneys are much more aware of the likelihood of premature failures and the possibility of litigation.
Faced with significant increases in their insurance premiums, many contractors and architects are looking at developing internal risk management programs. As part of those programs, they need a specialized consultant to help them address the building enclosure for higher risk projects such as condominiums.
A look back
So what is the problem? Who is to blame? Is it a design or construction problem? Well, one thing is for sure there are many theories. So here is another take on it. As a first step towards understanding why we are having problems today, one has to look back to understand what may have led to these problems.
This article attempts to shed some light on how buildings built today are fundamentally different than those we built, say, 80 years ago. And as a result of those changes, why we have to do things differently today than we did 80 years ago.
So what is different? Lots, here are a few key differences:
There are other differences, unrelated to construction, that are a function of the society we live in. Some of these include:
By understanding some of these fundamental differences, we have a better chance of reducing the possibility of premature deterioration. Focusing on the first three key changes building form, materials and energy conservation we can develop a clearer, more effective approach to designing and building.
Buildings today are more complex shapes, meaning many more transition details that are likely locations for water penetration. The buildings of yesteryear were simple. They were often rectangular, with overhangs or cornices, and rarely had balconies. Our forefathers understood that by adding an overhang, eyebrow or cornice, you reduced the amount of water that landed on the walls.
So, do we go back to rectangular, simple buildings with big overhangs? Well, no. We can build buildings that are complex and visually interesting, but we have to address the fact that they require more attention to detail during design and construction. In many cases, the drawings do not include adequate information on how to construct these transitions, and the weather tightness is left up to a line in the specifications that requires the contractor to make the building "water tight."
Contractors, by the way, are expected to build more complex structures under tighter schedules and with a less skilled labor force.
The result is major problems can occur because the contractor doesn't understand the sequencing of key components such as weather-resistive barrier and flashings. We see it everyday. For example, many buildings have problems due to a lack of integration of flashing with the weather-resistive barrier at the balcony-to-wall interface.
The current process isn't working. Even with more thorough detailing and diligent construction, problems can still occur if an inappropriate building assembly is used or the design team failed to recognize the assembly's construction limitations.
Assemblies that rely on construction perfection are doomed to fail. Buildings are built outside with large tolerances and each is unique. They are not constructed in manufacturing plants with tight quality control. We need to accept the fact that construction isn't perfect, likely never will be, and accommodate this with our designs.
We used to build out of brick, solid wood and plaster all inherently durable materials. We built multiple widths of brick rather than veneers, giving walls of older buildings large moisture storage capacities. These assemblies work by storing moisture, then drying out.
Today we build out of wood-based products, gypsum and steel studs because they are less costly and allow us to build quickly. These materials are a lot less tolerant of moisture, but more importantly have a much lower safe moisture storage capacity than older materials.
So now we can tolerate less moisture, but we are letting more moisture get in due to the higher exposure conditions and more complicated enclosures.
We are also faced with more material options than ever before. Building product reps show up to ply you with information about how their product is better than their competitor's and how they have seen buildings fail as a result of their competitor's product. Be wary of such pitches. While many reps use technical jargon, their level of understanding of the technical issues is occasionally misguided.
A major difference between the walls we used to build and today's walls is the amount of insulation. We are more energy conscious and thus use a lot of insulation, but we need to understand how insulation affects wall performance. Because of how we typically insulate, building materials on the exterior of the insulation remain colder.
Old buildings got wet and the heat from the interior dried them out. Adding insulation significantly reduces the ability of walls to dry out.
We also use materials that are impermeable to water vapor transmission where we shouldn't, further limiting the drying of assemblies.
Where do we go from here?
Like any good 12-step program, the first step is admitting there is a problem. The problem is that walls, materials and expectations are fundamentally different than they used to be.
Understanding that we have the potential to let more water in, that we use less moisture-tolerant materials and that we have reduced the ability of walls to dry is a huge first step towards avoiding problems.
It is possible to design and construct a durable, cost-effective building enclosure within these parameters. But a few more things are also important, such as selecting the appropriate window and wall assemblies. Do you need a rainscreen or is a face-sealed assembly sufficient?
The building form and exposure should be carefully considered in order to select the appropriate assembly. An appropriate assembly must tolerate when, where and how much water is expected, because even small amounts of water can cause problems. The assembly should also provide underlying materials an opportunity to dry, even with less heat from the interior.
We also need to pay more attention during construction. This requires more focus on details at transitions, mock-up of key details to ensure that trades involved understand the sequencing issues, water testing to confirm performance, and regular inspection to maintain quality control.
Some still don't believe that it is necessary to flash windowsills or that a lot of water can penetrate brick or stucco. These realities can only be appreciated through investigating failures and, more importantly, understanding the mechanisms that cause failures. Understanding how things get wet and what it takes to get them to dry is key; it requires knowledge, training and experience that few possess.
We are learning from past mistakes and applying new knowledge to build successful building enclosures. Confidence has even been restored in the Vancouver multi-unit residential market, propelling it to new heights. Seattle has the potential to experience a similar feat.
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