How to Achieve a Tight Building Envelope
- By Ellen Kollie
- June 1st, 2012
“A tight building envelope provides a continuous thermal barrier and air and water vapor barrier,” says 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. “If done well, a tight building envelope provides energy efficiency by restricting the movement of air and passage of heat, and it eliminates mold issues by restricting the passage of water vapor.”
When it comes to campus facilities, administrators always want a tight building envelope. This begs two questions: How can it be achieved, and how can it be done better on new facilities than it was on older ones? Here’s how.
There are several things to focus on in terms of creating an overall tight building envelope.
Continuity of transitions.
There are a number of areas where building parts meet: foundation to wall, wall to window, wall to roof, wall to wall. More specific examples include where a curtainwall attaches to a precast wall or a masonry wall joins a stucco wall. It’s important that all of these transition spots are well joined. “If you don’t get it right, you have a weak link, and you’ll get heat escaping and cold air entering,” says Kikta.
Compatibility of materials.
There are a number of air barrier products that can be used to create a tight envelope at transition points, including sheet membranes, silicone sheets, sealants, and spray foams. However, certain materials, when used together, cause a degradation of one of the materials, resulting in a loss of tightness. So the compatibility of different materials must be taken into consideration before construction begins. “It is a straightforward process for architects and contractors to check with manufacturers about compatibility,” 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. “But it is a step that is easily overlooked.”
Constructing an eight- to 10-ft. section of the facility’s wall components on the building site and checking the mockups with the contractor to validate that everything is being done right goes a long way towards ensuring a tight building envelope. Additionally, a sophisticated owner will hire an outside group who will determine what testing will be done on mockups, says Baron, who co-chairs the Building Enclosure Council of the Boston Society of Architects. This is especially critical because, once a building is complete, it’s costly to address challenges.
This systematic and documented process, which primarily ensures the owner’s operational needs are met and building systems perform efficiently, is now standard practice. “There is a cost to it,” Baron admits, “but it shouldn’t be substantial compared to long-term savings. Still, when you’re looking at first costs, it can be a difficult pill to swallow.”
Doing It Better Today
The experts note three industry trends that also can help achieve a tight building envelope.
The first is an air and vapor barrier transition assembly. Building connections must be compatible and sequenced appropriately to withstand maximum wind loads; building movement due to thermal, seismic, and moisture content changes; and creep. An air and vapor barrier transition assembly is designed to bridge continuously between window and/or wall openings and the adjacent air and vapor barrier materials. Comprised of materials such as pre-engineered, finished aluminum and silicone materials, an air and vapor barrier transition assembly’s design absorbs thermal movement and wind-loading stresses. Because these systems are not limited to just the window-wall interface, connections can be used at junctions between other assemblies within the building envelope where spanning of voids is commonplace, such as roof to wall, floor deflection joints, expansion and control joints, or any other location where a degree of movement is anticipated.
“The interface between the window and wall is a challenging spot to seal tightly and thoroughly to avoid air transfer,” 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. “Now, instead of using a bead of caulk in that gap, we make a boot around the window with…silicone, which is physically attached to the window and wall. The result is a cohesive enclosure with no gap to fill in.”
A second trend is that of warranties to guarantee the consistency of the building envelope’s barrier layer. “This is one of the biggest things I’ve seen recently,” says Kikta. “Suppliers are thinking comprehensively about the building and how the pieces go together and, as a result, are manufacturing a complete warranted system. This is in comparison to the past, where the roofing supplier and the air barrier/insulation supplier were separate and each had its own warranty. It allows for a more efficient facility, and that’s pretty beneficial, I think.”
“The main benefit to a comprehensive warranted system,” says Mike DuCharme, director of Product Marketing for Carlisle, PA-based Carlisle Syntec Systems, which manufactures roofing systems and more, “is one-stop shopping with a company that stands behind all the products. It helps to avoid problems. For example, if you did have moisture intrusion, you would have to pull the different suppliers together to determine where and what the problem is and how to resolve it. It could be as many as four to five different suppliers: one for each sealing system. And there could be a lot of finger-pointing instead of problem solving.”
The third trend is advancements in glass and glazing technologies that have greatly increased the overall performance of windows and doors. “Triple-pane glass utilizing combinations of Low-E coatings provides design flexibility and high performance values,” says Lance Premeau, LEED Green Associate, product and market manager with Wausau, WI-based Kolbe Windows & Doors, a custom window and door manufacturer. “A wide variety of glass coatings expand the options available to building designers, even to the point of maximizing envelope performance specific to an elevation or side of a building. Both window and door design has improved and evolved to perform in accordance with the most stringent testing criteria for air, water, and energy.”
A tight building envelope ensures that your facility is energy-efficient, safe, and healthy. Achieving a tight building envelope begins with an appreciation for its value, says Baron, and that is followed by paying attention to the details. “If you fall short here,” Kikta notes, “then anything you’re doing on the rest of the building is money lost because you’ll lose heat on the lost details.”