Bethesda Bungalows, known for its ultra-tight homes, incorporates a range of products to insulate and seal each dwelling it builds.
The firm’s KellyGreen home, being built on a small infill lot near Washington, D.C., was insulated in about four days, according to project manager Ryan Schulte. For starters, the basement’s concrete walls were covered with a Johns Manville Kraft-faced batt (R-19); above grade the company relied on Demilec Agribalance open-cell spray foam for walls (R-21) and the underside of the roof deck (R-38).Even though spray foam expands to effectively fill the wall cavity, Bethesda Bungalows also demands meticulous air sealing. “You have to make sure the installer goes back with a caulk gun to hit every gap or crack,” Schulte says. Typically, the installer will use Dow Great Stuff Gap and Crack Sealer to seal any remaining gaps or points of air infiltration on the home’s exterior walls.
“We have found that in order to create a tight home, we have to be concerned with air infiltration, rather than just the R-value of the insulation,” Schulte says. “Only by focusing on both aspects will a home be made truly tight.”
To ensure performance, a post-construction blower door test will provide a true indication of the effectiveness of the home’s thermal envelope, he adds.
INSULATION TIPS
–Avoid thermal breaks by sealing between all framing members.
–Treat the interior wall adjacent to the garage as an exterior wall and insulate it accordingly.
–Insulate the ceiling of the attic instead of the floor for a conditioned attic space. Use at least 10 inches of foam.
–Avoid using foam insulation for basement walls since no air barrier is required. Consider using batt instead.
–Shop around for the best price on insulation subcontractors; many are slow right now and willing to negotiate.
The insulation for the KellyGreen project took a bit longer than usual, Schulte says. Subcontractor Davenport Insulation ran out of open-cell foam and had to apply closed-cell to finish the job. With its higher R-value, the closed-cell foam will actually provide better performance, Schulte says.
“We value our green subcontractors who are committed to solving problems, and in this case our homeowner benefited from their initial mistake,” he says.
Jennifer Goodman is Senior Editor Online for EcoHome.
