Converting porch to living space — insulation plan
I have a 13×26 porch with glass sliders that’s on 6×6 posts about 18″ – 40″ off ground (ground slopes away from house) connected by glass doors to main living area. Roof is unvented cathedral ceiling, open to porch below. Currently about 6″ of soffit overhang on exterior, so not a ton of room to build out exterior with rigid foam if I want to preserve roof overhang.
We want to turn it into conditioned space (4 season) with 14 windows (sigh), and I have some questions on my insulation plan. I have read the FHB article on insulating a cold floor.
So, here are my ideas and questions:
Ceiling is currently cathedral, uninsulated with 2×8 framing. Only real option is closed cell spray foam to meet code is my understanding — correct? and is 7.25″ sufficient?
Walls are currently 6×6 posts. Option 1: 2×6 framing, with fiberglass bats, 1″ rigid foam on exterior, zip system. Option 2: 2×4 framing flush with interior side of 6×6 posts, fiberglass bats, 2″ rigid foam on exterior, zip system (this will leave exterior of my 6 6×6 posts flush with zip, and not insulated). Or another option?
Floor is currently 1×4 PT decking on 2×10 joists. Option 1: 3/8″ ply subfloor over existing PT, 4″ rigid foam underneath PT in joist bays, then 2-3″ of closed cell spray foam (I realize this will leave some thermal bridging of joists). Option 2: remove PT floor (a lot more labor), r-30 unfaced fiberglass bats between joists, 3″ thermax across bottom of joists.
Thank you in advance for your feedback!
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