Insulating an addition built on piers and insulating corners
I am starting a 16′ x 21′ addition that will be supported on 8′ tall block/brick piers. The floor will be framed with 11 7/8″ I Joists. I contacted an insulation sub for the insulation work. Here are the details:
23/32″ plywood sub floor
11 7/8″ I joists
Sub will apply R30 of Icyene open cell foam to bottom of sub floor (leaving approx 3-4″ air gap to bottom of joists
I will install 2″ XPS foam, then 15/32″ ply, Tyvek taped for air sealing, and vinyl soffit,
I like Dr. Joe’s “perfect floor” where the air space is under the subfloor, but that makes spray foam challenging due to the timing of the application. I may change to unfaced fg batts to maintain the air space between the subfloor and insulation.
This is the first project I have had with an elevated and exposed floor, so any comments are appreciated.
Second, I am building 2×6 walls with 1 1/2″ xps ridgid sheathing, sub quoted kraft faced r21 batts for the cavities. Interior will be 1/2″ drywall, primed, and painted. It seems from what I’ve read that kraft faced should not be used in this wall set up. Am I wrong in my thinking?
and for the corners I will install 15/32″ plywood for bracing and 1″ XPS to match up with the rest of the walls. The width of the bracing will be 32″. This puts me below the recommended thickness of foam in the corners. Does that pose a problem where I should increase the rest of the foam to 2″?
Thanks for any responses, I appreciate the time — Dave
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