Basement and crawlspace insulation should not be forgotten. This is where the house meets its foundation and there is a significant amount of air infiltration. The foundation itself has very low insulation value. We always recommend that the rim joist be sealed and insulated with spray foam.
Finished basement projects should include foundation insulation but it is important to choose the right system. Traditional batt insulation will lower the temperature of the foundation without controlling the moisture flow, which is critical below grade. With a lower surface temperature the potential for condensation goes up. Traditional vapor barriers such as polyethylene cannot be used because they invariably will trap moisture and lead to mold and decay.
We recommend closed cell spray foam for this work. It is impervious to moisture, controls vapor flow and prevents condensation. It also insulates to a very high standard and since it is sprayed directly against the foundation, there are no gaps or hidden pockets that can promote moisture accumulation and mold growth.
The foam is applied after the interior wall framing work is complete. Build your walls with a one-inch offset from the foundation so that we can spray a monolithic layer of foam behind the framing.
Crawlspaces used to be treated as part of the outside. They were built with ventilation openings which let in ice cold air in the winter and hot, humid air in the summer. Both are bad. In the winter, floors above crawlspaces are very cold. In the summer the moisture laden air can lead to mold growth. Today we insulate and air seal the foundation and rim joist with closed cell spray foam. Warm air from the basement heats the crawlspace, which increases comfort. If the crawlspace has a dirt floor, a vapor barrier must be installed to seal out any ground moisture before the foam is applied. Crawlspace conversions are cost effective projects with immediate benefits.