Crawl Space Insulation Myths

Some crawl spaces have insulation in the floor above, but the in reality the insulation isn’t helping much.  One reason people insulate the floors above their crawl spaces is to keep them warm in the winter when cold air is coming in the vents.  These vents should be closed permanently, which would make a huge difference in the temperature of the floor above.  Then the insulation would not even be necessary.

Fiberglass insulation only works in a closed cavity because it’s loose and allows air to pass through it.  When it’s between floor joists in a vented crawl space with the foil side up and the unfaced side down, it’s not doing much at all.  Also, paper-faced insulation provides the perfect environment for mold to grow.  Mold loves paper facing even more than it loves wood!

Foil-faced insulation is supposed to be a radiant barrier, but in reality, it creates a thermal bypass, meaning air can flow on both sides of the insulation, rendering the insulation useless.  Also, when fiberglass insulation gets even a little bit damp, it loses a whole lot of its value.  Overall, the insulation in your crawl space isn’t doing much for you at all.