The spray foam versus “other” insulations discussion seem endless, with cost being a major factor in decision making. Does any one have experience with or opinions on flash sealing with foam and using batts after that? I just met with a foam contractor who recommended such an approach, given that the strength of argument in favor of foam is its air-seal capability, not R-value. He was recommending an inch or less of foam to seal then R-21 batts as a cost effective alternative to several inches of foam.
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That has been recommended here a few times.
There is some good theory behind it apparently.
I have no experience or opinion on it.
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I cannot give you a complete answer, but one of the issues has to do with your climate and the location of a vapor barrier. Generally closed cell foam can provide a sufficient vapor barrier IF it is applied in sufficient thickness for your climate. Open cell foam is more permeable to vapor.
The minimum thickness may be different for roofs versus walls.
I hope this helps steer you in the right direction.
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I'm liking the JM Spyder for walls here in NC where we have reversing vapor drive and strong drying potential. It needs a tight wall for bulk air movement but if you are detailing your drainage plane and spray foaming the top plate you've got that pretty well under control. In my houses I save the spray foam for the roof (and shoot 8" to 12") Further North the flash and batt seems to make more sense to me.
M------------------
"You cannot work hard enough to make up for a sloppy estimate."
I think flash and batt sucks. You need at least 1 inch of CC for vapor barrier. I would find someone who can spray 1" cc then fill with OC. Filter glass is what I call the4 pink stuff. air moves right through.