Writing from Climate Zone 3, Farm House seems to have worked out many of the details for the dream house he plans to start building in a few months.
“Plan to live in it for 30+ years,” he writes in a post at the Q&A forum at Green Building Advisor. “The house will have Zip System sheathing and will be well insulated on the inside. I will just leave it at that. Not interested in installing rigid foam on the outside of the roof sheathing. (I have my reasons, so please don’t try to convince me otherwise.)
“So, house fully exposed to sunlight. One inch rigid foam with foil facing. Strapped with fiber-cement siding.”
That’s the plan: no rigid foam on the roof, but 1 inch of rigid foam on the exterior walls, plus a vented rainscreen and siding.
The Farm House challenge? “Sell me on all the reasons this [rigid foam on the walls] is worth the time and cost.”
Not our job to sell anything
“First of all,” says GBA senior editor Martin Holladay, “it’s your house. You can build it any way you want, as long as your local code enforcement official is happy. I don’t see any reason to convince you of anything.”
That said, if Farm House decides that it’s a good idea to increase the R-value of the wall assembly or reduce thermal bridging between the studs, he could take the advice of Steve Knapp and use Zip System insulated R-sheathing, which combines structural sheathing with foam insulation.
R-sheathing can take the place of conventional OSB or plywood sheathing. It comes in various thicknesses, with R-values ranging from 3 to 12.
“But I see no reason to try to convince you.”
Skip the exterior foam and invest in PV
Dana Dorsett won’t…