How to insulate behind a kneewall in a finished attic?
I have a finished attic in my vented roof home. The vent’s size is about 50-60% of the length of the roof.
The attic level is 27′ wide 40′ long, with the soffits running along the 40′ length. About 6 feet in from the soffits on either side is a vertical finished wall that meets the ceiling. R-11 batts run the width of the home in the 12″ floor joists, and the insulation is also placed in between the rafters from just above the soffit to the vented and non-vented portions of the roof, and also behind the kneewall.
The space desperately needs air sealing and additional insulation as it is responsible for at least 1.5ACH on that level alone.
I got a few quotes with multiple different approaches, (closed cell, foam boards on rafters, blown-in, duct-sealing) but all quotes were too expensive (10k+) for my taste so I am going to do it myself.
I am primarily interested in placing 4″ of foam board behind the kneewall and between the joists below and air sealing with can foam, adding baffles to the rafters to prevent wind washing and also blowing in ~12 inches of cellulose
I am curious though about the viability of placing foam boards on the rafters themselves and air sealing there. I am not sure what the implications of this would be in my open vent design roof… but I also already have batts in the rafters… would I be creating a problem by foamboarding over the rafters from soffit to the top of the knee wall?
Would the baffles not effectively create an air seal between the roof and the attic by themselves anyway? In which case, if I use the foam board on the rafters, do I even need baffles?
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