I posted this to the Insulation BBS, but I saw an unanswered question on this subject here, so I thought I'd ask.
I'm adding ventilation to our 55-year-old ranch style home. The entire roof is a hip-roof (no gables), with about 300 feet of gutter attached to sealed soffits that drop down about a foot below the top of the 9" brick exterior wall.
There are two small "gable" type vents at each end of the main roof peak, and no soffit venting. Moisture wasn't really a problem until I started going into the attic to work on the house wiring, but the heat up there in the summer has now come to my attention. My guess is that it gets up to at least 150 degrees in the attic during peak August sun. There's currently about 16" of 1970's vintage blown-in insulation up there, but I've been moving it around a bit. I figure that as long as I'm dealing with the heat situation, I'll be stopping any future moisture issues. Right now, I'm working at the top of the exterior walls, but I'll be adding soffit/ridge vents at a later time when I do some more math.
I've got a few pictures of what I'm doing at
Each rafter is plugged at the outside of the exterior wall with a 2x6, nailed from the soffit side (remember that this house has 300' of SEALED soffit). What I'm doing from the attic side is using a Speedbore bit with an extension and a Sawzall to cut a 1" high slit in the 2x6 where it meets the roof decking. I'm then notching the ProVent rafter baffles to get a better seal against the 2x6.
My question is this:
How concerned should I be about getting a perfect seal here?
Spray foam does not stick to overhead surfaces very well, and I'm concerned about it expanding into the slit in the 2x6. I've also thought about craming some fiberglass batt insulation into the area where the baffle meets the 2x6, and then inserting more uncompressed fiberglass insulation until I reach the inside top of the exterior wall (resulting in about R-15). I've also thought of making rigid foam insulation cutouts that would fill basically cover the inside of the 2x6 (ADOVent makes cardboard cutouts, but not to fit the 16" on-center of my rafters).
Or should I not really be concerned about air leaks at all, and just spread the cellulose insulation all the way to the 2x6 and top off the attic to 16" when I'm done?
As a side note: baffles are useless at the inside corners of this hip roof (almost 3 feet each way from the corners). Should I fill in those areas to the roof decking, or should I just cover the attic floor and leave an air space between the cellulose insulation and the roof?
Thanks in advance for your help.
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