Replies

1. GBA Editor
   Martin Holladay | Jul 27, 2011 05:33am | #1

   Todd,
   You're asking for the BEST details, not the cheapest.

   First of all, fiberglass batts should never be used to insulate a rim joist. Because fiberglass batts are air-permeable, they allow the moist crawlspace air to contact the cold rim joist. As a result, the rim joist accumulates moisture all winter long, until it rots. Building inspectors see these rotten rim joists all the time.

   Rim joists should be insulated with either closed-cell spray polyurethane foam or rigid foam. If you use little rectangles of rigid foam, be sure to seal the perimeter of each rectangle with caulk or canned foam.

   Because the pony wall faces a potentially damp environment, I would advise that fiberglass batts shouldn't be used there either. My advice is the same -- closed-cell spray polyurethane foam or rigid foam are your only options.

2. 
   e2BhHeMrFZ | Jul 27, 2011 06:43am | #2

   Thanks Martin. I should add one thing that more specific than the climate zone I am in central NC and termites are a real concern. Do you have any concerns or counter measures using either of these techniques with regard to performing routine termite inspections?

3. GBA Editor
   Martin Holladay | Jul 27, 2011 06:47am | #3

   Todd,
   Termite issues complicate the use of rigid foam. Because local practices and codes vary widely, you should contact your local building code official to determine how you can insulate these areas while still complying with local codes and practices.