Expert: Dave Johnson - 12/11/2008

Question
I have a 15 x 15 three season room.  Just had the walls and ceiling insulated.  Installed new double pane, low-e windows.  The original floor was 2x6 decking, and installed 3/4 plywood subflooring and porcelain tile on top of the decking.  I live in Maryland, which can get quite cold.  Underneath the room is about 18 - 24" open space on three sides.

My question is, do I need to insulate underneath?  Seeing how it is virtually impossible for someone to crawl underneath to insulate, can I put 1" or so sheets of insulation vertically around the outside opening of the underneath and dress it up with lattice or something?  What is the best way to insulate if I can't get underneath?

Thanks so much for the help!

Answer
Hi Jim,
Ideally, you should do the floor, and if it is 18-24", there should be enough room. If you can do it this way, insulate with 2" of foam board between the joists.

Otherwise, the perimeter can be done with the same material, but it needs to be as tight as possible. (a sealed crawl space will not get below 40 degrees, but that will also be the temp. of your floor material.
Thats why its better to do the joists, 'cause you can push a little heat down, making the floor a bit more comfortable.

Best of luck,

Dave