Creating Tight Building Envelopes
- By Ellen Kollie
- June 1st, 2012
“A tight building envelope is one that provides a distinct separation between interior and exterior conditions,” says Jonathan Baron, AIA, LEED-AP, an associate with Shepley Bulfinch, a Boston-based architecture and design firm with offices in Phoenix and San Francisco. “A high-performing enclosure restricts the free passage of heat, and air and water vapor, through a wall or roof. This separation results in buildings that use less energy, suffer few moisture or mold problems and last longer with less maintenance.”
When it comes to creating tight building envelopes, there are two objectives. “One is energy conservation and the other is protection against water infiltration,” says Mike DuCharme, director of Product Marketing for Carlisle, Pa.-based Carlisle Syntec Systems, which manufactures roofing systems and more. “Both are equally important.”
Here, experts share their thoughts on what to keep in mind as you work toward these two objectives.
: “We believe that the coordination of the trades is absolutely critical to a tight building envelope,” says DuCharme. “You may have as many as five trades involved in the installation of the roof and wall vapor barrier systems, sealing around the windows and waterproofing the foundation. If they’re all operating independently and disconnected, then where one stops and the other begins is where there will be problems.”
DuCharme also notes that coordination of the trades ensures that all the products are compatible. For example, if you choose an asphaltic product to tie into a membrane, the asphalt could swell and distort the membrane so that it lacks a tight a seal. Similarly, solvents on some products could eat away at the adjacent product.
2. Air Barrier and Transitions
: Key to a tight building envelope is a continuous air barrier. “While the specified material — sheet, fluid applied or other — is important,” says Baron, who co-chairs the Building Enclosure Council of the Boston Society of Architects, “the most attention should be paid to transitions across materials, especially connecting an air barrier to windows or door frames. Any uncontrolled gap is a chance for the assembly to leak.”
Thomas Kikta, AIA, LEED-AP BD+C, senior project manager with Chicago-based Legat Architects, and who specializes in identifying and repairing sources of moisture intrusion to make facilities energy efficient, safe and healthy, agrees. “If you don’t get the detailing right at the joints, and if you don’t have continuity, you’ve
got a weak link allowing air infiltration/exfiltration,” he explains.
Kikta also notes that many manufacturers are working to ensure system continuity. For example, commercial aluminum windows now have thermal breaks between the interior and exterior sides of the aluminum frame; metal doesn’t extend uninterrupted from the outside to the inside. This helps keep the hot side hot and the cool side cool.
: To ensure tightness, a variety of testing methods are available. One is creating a standalone mockup before actual construction begins. “As early as possible, we’ll sequence construction and build and test 15 feet before we do the entire building in order to prove it works before construction begins,” says Chad Dorgan, P.E., Ph.D., LEED-AP BD+C, CxAP, CCP, vice president of Quality and Sustainability for McCarthy Building Companies, Inc., a construction firm with 12 offices across the country. “The testing has a little time and money cost associated with it, but it is much more time and cost effective than making repairs after the fact.”
Similarly, whole-building testing is another way to ensure tightness. “Large fans are placed within exterior door openings and are used to pressurize and depressurize the building,” says Baron. “By watching how hard the fans have to work to get to a specified pressure, the tightness of the envelope can be quantified. By using small smoke generators, testers can find the location of leaks and they can be sealed.”
McCarthy uses nondestructive testing on all of its projects. “We used infrared (IR) testing on the roof membranes for Barry Goldwater High School in Phoenix,” says David Knochenhauer, McCarthy’s Southwest Region Quality Director, referring to a recent renovation/addition project. “This allowed us to make sure there wasn’t water infiltration that occurred prior to our beginning work and again when the project was complete.”
4. Window and Door Quality
: There are numerous products available to building administrators that contribute to a tight envelope, including windows and doors. “Window and door systems are designed, built and tested to meet high-performance standards for air and water infiltration, as well as overall energy performance,” says Lance Premeau, LEED Green Associate, product and market manager with Wausau, Wis.-based Kolbe, a
custom window and door manufacturer. He notes that there are a few performance values that are specific to these products, such as U-value, solar heat gain coefficient and sound transmittance, which can be utilized in the envelope design.
: As already noted, McCarthy is currently working on the $25-million, 330,000-square-foot Barry Goldwater High School remodel project. In Phase 1, the team installed more than 100 exhaust fans/outside air intake vents and 75 windows in the existing building. “Our challenge was needing a temporary window protection that we could take on and off a couple of times while we cut the hole, installed the frame, and glazed and caulked it, while keeping the building watertight in the process,” says Project Manager Ryan Cogley. “Our solution was ¾-inch plywood, cut to a little larger than the window, coupled with a neoprene gasket and masonry screws.” In addition, the team used a 100-percent silicone sealant when installing the windows, as they found it a more reliable product than polyurethane, providing a longer life span around the windows and penetration.
: One of the challenges of replacing the roof on Barry Goldwater was that the work was done during Arizona’s monsoon season, where most of the year’s rain falls within a single month and microbursts with wind gusts between 60 and 70 mph are not uncommon. “The team identified the monsoon season as a risk,” says Knochenhauer, “so we implemented temporary methods to protect the interior space from water infiltration that could start microbial growth after the building was sealed.”
“Because it was a foam roof,” Cogley adds, “we bought foam packs, which are temporary, two-part foam canisters that we sprayed when we put the equipment curbs on the roof. It stuck to the existing roof and provided a temporary seal until permanent foam installation could be used. That enabled us to keep moving on installation of the air intakes and units without having to wait for the roof subcontractor to come back and patch.” Knochenhauer adds that this protection method prevented potential moisture from migrating horizontally across the metal roof deck and being trapped under the roof system.
The experts at Legat Architects in Chicago are also replacing a roof, as part of a renovation project, on Chicago Public Schools’ Henderson Elementary, a 90,000-square-foot school built in the 1920s. The roof was originally designed with little to no insulation. “We’re installing four inches of polyisocyanurate insulation,” says Kikta, “which will give the roof system an R-value of approximately 22, thus meeting current ASHRAE standards.
“When the contractor is tearing off a section of the roof,” Kikta continues, “he is covering it with a vapor barrier that also serves as a temporary roof that is almost like a mini built-up roof. We’re putting a modified bitumen roofing system on top of that.”
: Henderson Elementary is built of foot-thick brick walls with plaster on the interior, all of which serves to keep water out. For this project, the masonry is being restored, including grinding and tuck pointing to tighten the mortar joints, and the rebuilding of parapet walls that were showing excessive deterioration. Here, the team is wrapping the roof membrane up to the back of the parapet wall and tying it to the flashing.
Then there are the lintels. The team discovered that they were not flashed so that, once water hit them, it could go anywhere, including into the building. “Fortunately, we found only some surface rust and that less than 10 percent of the lintels needed to be replaced because of extensive deterioration,” says Kikta. “The other 90 percent are being prime painted and properly flashed to ensure that the water entering the wall system will be directed out via weep holes to keep the building dry. That will also help tremendously in terms of heat loss.”
With attention to detail, it is possible to create tight building envelopes that conserve energy and protect against water intrusion. The benefit is schools that last 100 years, as intended. In addition, tightening the envelope on renovation projects can add 25 or more additional service years to a school. And that is satisfying indeed, notes Jason Lembke, AIA, LEED BD+C, Legat’s director of K-12 Education: “It’s important that these facilities remain warm, safe and dry. By renewing the building envelope, we’re giving the building a second life span for the next generation of students.”