Although the envelope is not considered a glamorous or show-stopping element of a home, it arguably is among the most important considerations when remodeling or building to ensure a tight and efficient structure. The ideal building envelope varies by region and requirements vary by jurisdiction, but managing moisture is vital no matter what.
Building enclosures can include the following products: interior finishes, air/vapor/weather barriers, framing, insulation, ventilating air spaces and exterior weather repellant finishes. Judd Peterson, AIA, Chair of the Building Enclosure Technology and Environmental Council of the National Institute of Building Sciences, and director of building science for Minnetonka, Minn.-based Judd Allen Group, notes many higher R values for enclosure insulation is in an effort to meet upcoming 2030 guidelines in cold or very hot climates. These regulations will approach R-30 for walls and R-50 and R-60 for attics. “Studies have found significant heat loss even through concrete footings in warm, 50 F soil so we’re seeing even footings wrapped with rigid insulation,” he says.
Jennifer Frey, product manager with Henry Co. notes the majority of the company’s new products are spurred by customers requesting new technologies. A lot of those new technologies, she says, first are introduced in commercial spaces before evolving to residential spaces. “Commercial is a lot tougher than residential so it’s a great trend to have that technology coming into residential because it can be proven in a very large-scale structure before it reaches someone’s home.”
Code requirements vary quite a bit between commercial and residential, especially relating to fire ratings and building height considerations. “The important part of the commercial to residential comparison is commercial construction puts a lot of emphasis on what’s in between the walls to ensure the building will perform as the architect intended,” Frey explains. “In residential, sometimes consumers are more interested in putting focus on things they can see, like fixtures. You want to ensure you’re proud of your home and building, but if you have the opportunity to remodel or build, the focus on what’s between your wall shouldn’t be ignored.
“There are codes that are striving to have a continuous barrier to achieve energy ratings,” Frey notes. “A lot of builders are doing that every day and it’s not new to them; for others it will be brand new. In commercial, they achieve that continuity to a greater degree than what residential currently does.”
Continuity in envelopes
Continuity is crucial when constructing an effective envelope. “Continuous air barriers are more critical than ever,” Peterson says. “We’re seeing continuity of the air barriers inspected and verified by third-party commissioning specialists to eliminate gaps; drilled hole violations; framing joints and gaps; and full, sandwich-sealed, perimeter window flanges wrapped with self-adhering, self-sealing membranes bonded to themselves at the ends of the window flanges and to the sheathing at perimeters of all penetrations and flanges.”
More liquid and spray-applied barriers are being used because of the demand for continuity, bonding and self-sealing characteristics. Insulation also is being placed more continuously to eliminate convection and air infiltration gaps using staggered double-stud framing or spray-foamed cavities.
Frey notes commercial spaces often use liquid-applied air barriers because they have no seams or breaks. “But that’s an application method residential installers aren’t as keen on, I think,” she says. “That product has evolved from mechanically fastened materials to self-adhering to help achieve that same feeling of continuity.”
Peterson is seeing higher quality below-grade waterproofing products applied to foundations, under slabs on grade and around elevator pits. “The cost of correction of a below-grade water leakage is severely expensive – five to seven times the original cost of application of waterproofing. In other words, the cost of quality waterproofing is relatively insignificant in comparison to corrective costs of failure of a less effective waterproofing. Damp-proofing a foundation is futile, and not recommended.
“We’re also seeing ¼- to ½-in.-deep air ventilation planes toward the exterior, just under the exterior finish cladding, to evaporate moisture buildup within the enclosure,” he continues. “It’s very similar to masonry cavity wall construction with a ventilated cavity; we’re seeing the same principles applied under wood sidings.”
George Caruso, Benjamin Obdyke’s Manager of Product Development, is noticing increased interest in moisture management. “I see the inner section between moisture management and energy efficiency as a focus,” he says. “As you make a home tighter it becomes less forgiving to moisture issues. As moisture gets in there and gets trapped, you need mechanisms in place to manage it. There has been a discussion around vapor permeability in wall construction for a long time. As you put foam into a wall it reduces the wall’s permeability because you’re trying to achieve an enhanced R-value. That requires better moisture management because it’s reducing the wall’s drying potential.”
Oregon, for example, recently adopted a new code that requires enhanced moisture control in walls. “They originally tried to push language that would require a rain screen,” Caruso says. “They were following what was put in place in Canada, where they do require a bigger gap. Canada is more conservative in its approach to building envelopes. Ultimately, Oregon decided to instead incorporate drainage into the wall.”
A rain screen creates a gap to decouple the siding from the house wrap and allow space for any water that penetrates to drain and the space to dry. “You’re introducing airflow behind a wall,” Caruso simply states. But because of the added cost of rain screens, not all markets require their use, which is where drainable house wraps can be of use. Drainable house wraps are enhanced from a traditional house wrap by creating some space, though not as much as a rain screen does. “It’s not true ventilation and airflow, but it uses 1 mm spacers to provide a small standoff to allow gravity to take over and water to get out. The path of least resistance becomes down and out of the wall.”
Frey also has been hearing about regions having certain codes relating to moisture. “I think it’s all relative to where you are,” she says. “The big request I commonly hear is different application methods to accommodate situations. Some people may install the building wrap differently to accommodate local code around jams or headers. We can’t always assume one size fits all. The international code has been established; it’s just a matter of certain states catching up.”
“In the end, a small omission or oversight in execution can defeat an otherwise well-designed enclosure,” Peterson asserts. “The last five percent of effort put into each performance plane has to be as meticulous as the first 95 percent. With that consistent attention, there usually is no problem with performance.”