Hello – I am seeking input on insulating for a project. I am converting an existing screened porch to a sunroom and have been searching for tips. I am in Eastern NC (hot and humid summers), and the floor of the porch/sunroom is 4 feet above ground. I plan to lay roofing fabric on top of the existing boards (in good shape), then concrete backer board and then tile for the interior floor. I will have a mini-split system to heat/cool the interior as well. Below the floor is where I have questions.

I plan to put 8″ R30 batts between existing joists (unfaced). However, I thought I would also use spray foam to seal the inside perimeter of the frame, screw in rigid foam board, tape/seal joints. The exterior of the frame will have cement board siding (and sealed underneath).

I have doubts about using the foam board. I have read and seen some videos that recommend it to keep the joists dry and insulated, and I have seen others that say absolutely not and to use plywood or just a wire screen underneath. I don’t want to trap any moisture that could leak into that space and have mold issues over time.

I appreciate any and all input here. Thank you.