Insulation Between Floor Joists Over A Crawl Space

When the basement or crawl space has vents installed insulating joist bays.

Insulation between floor joists over a crawl space.

In moderate or dry climates without the threat of sustained subfreezing temperatures insulation between floor joists makes sense. Instead install fiberglass batting between the joist bays which are the spaces between each set of floor joists. Department of energy recommends r 11 3 insulation under floors in warm climates and an r 25 6 to 8 in cold climates. Floor insulation for moderate climes popular reads.

Use caulk or foam sealant to seal the joint between the top of the crawl space wall and the sill. Moisture laden fiberglass becomes heavier and begins to sag and fall. However the insulation needs to be treated with a fire retardant. While this method does work in the very short term moisture eventually builds in the crawl space and grows on this highly porous surface.

If your space has them avoid adding insulation to the crawl space walls. It is important to secure insulation and cover it with a vapor barrier in order to prevent moisture and the mold that often follows close behind. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls. This type of crawl space also allows insulation with an r value of 19 installed in the floor joist if the crawl space and has a permanently installed dehumidifier.

Crawl space insulation basics. Don t compress the insulation as it requires its loft in order to maintain its rated r value. Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances. Where winter temperatures are extreme opt for insulating the walls and sealing off the crawl space entirely.

If the crawl space is ventilated which is ideal because it aids in the elimination of moisture then fiberglass insulation can be easily installed under the subfloor between the floor joists. This type of insulation allows for conditioned air to be introduced into the crawl space. Unlike fiberglass rigid foam insulation does not absorb water support mold or allow air to pass through providing that joints between boards are sealed with tape.