Rigid foam as floor insulation - DIY Chatroom

rkhpapa · 09-23-2006, 05:26 PM

I'm converting an existing screened porch (New Hampshire) into a 3 season room. The floor is 5/4 X 6 decking which I need to cover and finish. I only have 1 13/16 to play with until I come flush with the existing threshold. I was thinking about 1" thick foil faced rigid foam directly down on that decking and then covering that with 5/8 T&G plywood. That would leave me somewhere around 3/16 or 1/4" for indoor/outdoor carpeting or some other finsh. Here are my questions:
-do I need "sleepers" to keep that foam from crushing or can I just screw the plywood down through the foam?
-if I do need the sleepers, how would you space them?
The floor is 16' across the joists by 10' deep.
Thanks for your thoughts.
Rich

redline · 09-23-2006, 08:47 PM

can you install the insulation on the under side of the floor decking?

rkhpapa · 09-24-2006, 07:33 PM

That's my problem. There isn't enough room between the grade and the floor joists for me to crawl under there. That's why I'm trying to insulate it from the topside.
Thanks,
Rich

fqp25 · 09-24-2006, 08:06 PM

Supposedly, you just lay down the polystyrene foam insulation, then the top flooring and screw it into the joist. I've only used it under durarock and tile floor. I don't know what kind of effect it might have with a plywood top, and a space that large.