I'm hoping I could get some advise on insulating and building walls in a room that is under an extension that was put on my house several years back. The room needs to be fairly air tight, and has a few unique features, such as:
A) plywood over the previous exterior wall
B) the original foundation, flush to plywood (A)
C) cinder block foundation for the extension
D) extension walls, set back a few inches from foundation (C)
Right now, I'm thinking closed cell spray foam insulation for the entire thing might be the easiest and most effective way to go, but would love to hear some feedback and other suggestions as well. Regardless of the approach, some additional questions I have are:
1) Should the wood and/or entire area first be treated with with something to prevent mold?
2) Is there any benefit to using spray foam over boards? Would board create an air tight space?
3) I am under the impression that lumber used to frame the walls can be placed right up against closed cell foam board. Is this also true for closed cell spray foam?
4) How should I deal with the varying depth between walls (C) and (D)?
Thanks in advance for any help you can offer!
Chris - Andover, MA