Peel-and-stick housewraps are relative newcomers to residential construction, and until now have been embraced mostly by high-performance custom builders. But a recent code change could open up a wider market opportunity for these products. The change is the requirement for air-leakage testing in the International Residential Code (IRC).
With insulation levels in new construction reaching a point of diminishing returns—where the cost of adding more R-value isn’t justified by energy savings—the IRC recognizes that the best way to squeeze more efficiency out of homes is to reduce air leakage through gaps in the building envelope.
The 2015 version of the IRC limits air leakage to five air changes per hour or less in Climate Zones 1 and 2, and three air changes per hour in Zones 3 through 8. The 2015 version also goes a step further by requiring builders to document those numbers with a blower door test.
Enter peel-and-stick. Like other housewraps, these products’ main job is to create a drainage plane between the siding and the sheathing—a secondary watershed in case rain or melting snow gets past the siding. Unlike other housewraps, they do a consistently good job at blocking airflow. Four prominent versions of peel-and-stick are Henry Co.’s BlueskinVP, Delta Vent SA, Grace’s Vycor enV-S, and Polywall’s Aluma Flash Plus. Builders who understand peel-and-stick’s benefits likely will be willing take a second look at these products.
Continuity is King
Air leakage is the product of a pressure difference between inside and outside, combined with a hole. With enough of a pressure difference between inside and outside, even a small hole can allow an enormous amount of air to escape or enter.
Besides wasting energy, air leaks can damage the building envelope by carrying moisture from warm, humid areas to cold surfaces (cold sheathing in the winter, or the back of cold drywall in an air-conditioned house in summer), where it can condense and set up conditions for rot and mold.
The key to minimizing or eliminating this problem is a continuous air barrier. The emphasis is on continuous: Joe Lstiburek, principal at Building Science Corp., says that discontinuity is one of the top 10 most common errors he sees. He also points out that continuity is easier to achieve with an exterior air barrier because there’s no need to detail around interior partitions.
Standard housewrap theoretically can work as an exterior air barrier, but it’s tough to detail correctly. In fact, field tests conducted by Oak Ridge National Laboratory (ORNL) have shown it’s a lot easier to do a good job with peel-and-stick.
Research sponsored by Grace Construction Products measured the performance of Vycor enV-S against a mechanically-attached housewrap. ORNL staff built two identical wall modules in a test home. Certified installers from each manufacturer installed the housewrap and detailed the openings. Researchers then ran blower door tests at various intervals over a 15-month period.
According to Andre Desjarlais, ORNL’s program manager for building envelopes, air leakage was “an order of magnitude higher” with the mechanically attached housewrap. He credits that difference to the two products’ relative ease of detailing. “You need to seal the air barrier to windows, doors, and other details, and you need to make the seal durable,” he says.
Desjarlais and his team found that sealing around penetrations with a mechanically attached product is difficult. Even when done by a trained installer, these details are much more likely to leak than with a peel-and-stick product.
Peel-and-stick products also should work equally well in both directions. Allison Bailes, owner of Energy Vanguard, did a series of blower door tests on the same house comparing the air barrier effectiveness of perfectly taped and detailed housewrap with that of a sheathing product with taped seams. (The housewrap was tested first, then it was removed and the sheathing taped.) He discovered that the housewrap was much less effective when the house was under positive pressure because air moving from inside to outside through gaps in the sheathing blew the housewrap out “like a balloon.” The assumption is that peel-and-stick will perform like taped sheathing because it’s fully adhered to the surface.
While peel-and-stick products have a long track record in commercial construction, manufacturers had to make some alterations in order for residential builders to accept them. Most important was a reformulation of the adhesive so that it sticks to plywood and OSB without the use of a primer. The goal was to reduce labor costs, which manufacturers knew would be critical for widespread acceptance by home builders.
A primer is still needed on substrates with loosely bonded surfaces, like masonry and gypsum board. It’s also a good idea on wood with a weathered surface. Test the surface by rolling a small section of WRB into place—if it doesn’t stick, use a primer.
Of course, the surface still needs to be clean and dry. “Adhesives have come a long way in my lifetime,” says Lstiburek. “But with all of the advances in materials science we have still not figured out how to get things to stick to mud, dirt, and frozen surfaces.” A broom should be sufficient for removing dirt and dust. As for water, a good test is to press the surface with a thumb; if your thumb gets wet, the sheathing needs more drying time.
Sharp protrusions should also be flattened or removed, and voids wider than ¼ inch should be filled with foam or sealant: Membranes aren’t meant to span gaps.
Finally, it’s a good idea to roll the membrane after installation. Some installers skip this step, but it’s important to making a tenacious bond.