Monday, August 11, 2008

Thermal Break(through)

Today, as I sat figuring the length of the roof rafters, a truck pulled up, and two guys with clipboards emerged to say that Clifton had sent them to talk to me about insulation. (I'd been discussing insulation a couple weeks ago with Clifton, a friend/architect.) These guys are installers of the icynene system. I'd read about icynene in a building magazine. It's a blown-in, open cell foam that's mostly water. Like other sprayed-on insulation, it creates a tight house, filling every crack and preventing outside air infiltration. If it has a downside, it's price. Probably double the price of fiberglass. What we're going to choose for insulation is still up in the air at this point. I've been planning to sheath the exterior of the house with sheets of rigid foam to boost R-value and create a thermal break with the outside. I mentioned this to the icynene guys. One of them had done the same thing for his house. He went to his truck and came back with a sample of what looked like a piece of felt weather stripping, one and a half inches wide and about a quarter of an inch thick. It was a high-tech strip of adhesive backed insulation designed to stick to a wall stud and create a thermal break with an R-value of about 4. I called the number on the sample, a distributer in Rhode Island, was quoted a price of 55 cents/ft. So I counted studs and plates and multiplied by 8 and got roughly 2000 ft. At that price it would be about the same as applying foam to the outside. But this would be far easier and faster to apply. Fasteners for the board and batten wouldn't have to be long enough to go through all that foam, and I wouldn't have to pad out the widows and doors with 2x4's to provide a foam-free nailing surface. Though it wouldn't provide the same over-all thermal protection as covering the whole house with sheets of foam, the thermal break is what you're really looking for when you go through the trouble sheathing with foam, and that's what this stuff does.

Tomorrow I'll be putting up the rafters for the shed roof. Big gable end rafters will follow.

1 comment:

Garrett said...

Hi there,

I've been trying to figure out the best way get the thermal break as well, and it sounds like your "felt stripping" is an ideal product. Do you have any info you could forward my way. Thanks for posting your project, Looks like a fun one!