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rtoni 09-19-2008 11:21 AM

insulating between rafters - no ridge vent
i have a vaulted cieling with ridge vent. the last section of rafter (where the lookouts run out across the gable end to the rake) is not drilled or otherwise open to airflow to the peak.

spray foam guy says his product will seal it up air tight - sounds great but but I don't have the $ in the budget to get him out.

thinking I have to drill the lookouts a close as I can to the top side to allow air from the soffit up to the peak. before I do, I have a question - can I do a foam board "fix" in that last rafter section instead - cut some 1 or 2 " rigid styro board (which I have enough of now from the crawl insulation leftovers), snug fit up in the sections between the rafters / lookouts, and run a bead of spray foam like the expanding stuff along the edges / seams to make these areas / sections air-tight from below? will this work? if so, should I do this at the top side (against the sheathing) and then fill the rest with roxul underneath, or fill with roxul 1st and then the foam board flush with the bottom face of the rafter?

hope i'm making sense...


rtoni 01-12-2009 10:16 AM

Hi all - resurrecting this older post as I'm 99.9% compete with insulation - I used Roxul (mineral wool batts) everywhere - the area described in this post is the only remaining spot.

Does solid foam - board cut to fit, with a bead of spray foam around the edges - work in an unvented space? My thinking is this will provide a thermal barrier and a complete air seal, much like if someone spray foamed against the underside of the sheathing...?

Any feedback would be appreciated

II Weeks 01-12-2009 12:35 PM

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sounds good. some guys dont like to totally air tight the sheathing and if your one of those guys, put in some baffles first and then do what you want with the rigid foam

rtoni 01-30-2009 04:14 PM

thanks II Weeks - appreciate the feedback....

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