Floors and crawl spaces
R-ll, R-13, R-15, R-19, R-21, R-25, and R-30 roll or batt insulation can be used under floors and in crawl spaces, as determined by the locally adopted building code and/or International Energy Conservation Code (IECC). When insulating floors over unheated basements or crawl spaces, faced products should be used.
Another strategy is to insulate the walls in well-sealed crawled spaces as an effective alternative to underfloor insulation. This
Figure 8.8 High-performance fiber glass batt. (CertainTeed)
Figure 8.9 Encapsulated fiber glass insulation. (CertainTeed)
method usually requires less insulation, minimizes temperature swing in piping and ductwork, and may even help cool the house in summer because some heat can escape through the uninsulated floor. It is critical that the space not have air leakage to the exterior, because this would allow heat to escape during the winter months.3
For insulating foundation walls of heated crawl spaces, use either unfaced insulation where the building code does not require a vapor retarder, or insulation with a special facing recommended for exposed applications. The insulation should be fastened to the sill plate and draped down the wall. The recommended R-value for this application varies by geographic area.