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Insulation for Attic Walls and Rafter Bays

gespo | Posted in General Questions on

Hey all,

A home energy audit of our 1930s house in Washington, DC revealed vermiculite insulation in the floor of the 300 square foot attic. Too bad the home inspector didn’t notice it when we bought the place almost two years ago. We are having the vermiculite removed this week, and trying to plan the best way to reinsulate. My spray foam research has repeatedly led me back to articles and discussions on this site, so I figured I’d throw the topic out and see if anybody had specific advice.

Our heat pump is in the attic, so encapsulating with spray foam seems like the best move. There are two gable vents, which we figure we should board up and foam over. We will run a bathroom exhaust that currently terminates in the attic a few feet further to one of those vents before sealing it shut.

Most companies are quoting us 4″ closed cell foam between the rafters (which are 6″ deep), and either 2 or 3″ on the stone gable walls, for something around R-30 (which doesn’t meet code). None brought up the issue of thermal bridging. Some have mentioned fire paint “to bring it up to code,” others haven’t, none have mentioned an actual thermal barrier.

Any thoughts on a configuration of insulation(s) that would best seal the space and hopefully meet code would be much appreciated. Perhaps something like this is an answer, but I haven’t found any mention of this specific product on the site.



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