Hello, first post here on the TOH website. I have a few questions regarding spray foam insulation. I am building an addition on the back of my house; a three season room to be more precise, and I would was thinking of using spray foam insulation. On a recent DIY home improvement show, they were touring a home where the owners had insulated the vaulted ceiling rafters; is that an acceptable method? Is there no need for "air space" between the insulation and the plywood roofing when using spray foam? Next question; my addition is constructed on 6-16" square brick piers, with the 2x12 floor joists being about 20" off the ground. I was planning on using the spray foam for that as well; any problems with that, is there something better/more efficient/more cost effective? Is there a big difference between open and closed cell foam? What about the soy based insulation? If it was used in the floor, would critters find it irrestible? Any help would be appreciated.

Thanks in advance,
Mark Roberts