A housewrap and rain screen in one
Delta-Dry weather-resistant barrier
• Manufactured by Cosella-Dörken Products
• 888-433-5824; www.delta-dry.com
• Cost: about 60¢ per sq. ft.
When I first saw Delta-Dry at the GreenBuild Conference, I was intrigued and confused. Wrap a house with semirigid impermeable plastic? That goes against everything I thought was housewrap’s main objective: to allow a building envelope to dry after it gets wet. Because Cosella-Dörken has a good track record for developing quality products and because big companies generally don’t spend money developing products that don’t work, I called the people who tested it.
What I learned was that rather than relying on the permeability of housewraps or rain screens, Delta-Dry creates a ventilation space on both sides so that air can flow freely behind the siding and over the exterior surface of the sheathing. That ventilation space is created by a system of dimples and channels that lets moisture condense and then either be dried by the airflow or be drained harmlessly to the ground. Unlike most housewraps, though, Delta-Dry is not an air barrier.
The 1/4-in.-thick wrap comes in rolls that are 39 in. wide and 50 ft. long, and the material can be cut with a utility knife. Delta-Dry is installed over plywood or oriented-strand-board sheathing. It is overlapped at seams just like typical housewraps and is fastened to the sheathing with 1/2-in. roofing nails or 3/4-in. staples from a pneumatic gun (a hand stapler won’t do an adequate job, no matter how many staples you use). Window and door openings are detailed using peel-and-stick flashing material. Delta-Dry is suitable for installation under brick, stucco, clapboards, vinyl, and shingle siding.
Photo, drawing: Courtesy of Cosella-Dörken