Combining Insulation Types

• Install the foam board first. Cut it to fit and then tack or wire it temporarily in place. The foam does not have to be well secured, but it must remain in place until the spray foam is applied. Spray foam around the foam board, letting the foam expand around the edges and fill the gaps between the board and the framing. Allow the foam to set, and then cut it flush to the board with a utility knife or drywall saw. Since the expanded foam will stick to the foam board and hold it in place, you can remove the tacking or wiring. If all crevices are filled with the spray, the combination of board and spray foam will provide a moisture-proof, sound-reducing layer of insulation.
  
  Neither the foam board nor the dried spray should extend beyond the edges of the framing, so buy the right thickness of board for the wall you are insulating. Since these materials provide their own moisture barrier, there is no need to install another one.
  
  Remember that even though foam has no nutritional value for pests, it is easy to bore through, so it may still become a nesting place for unwanted house guests. You can prevent this by taking normal steps for pest abatement, including periodic spraying of the foundation with orange oil.