Crawlspace Insulation
Free calculator with pre-filled dimensions • Updated March 2026
A 1,000 sq ft crawlspace needs about 21 batts of R-25 insulation (48 sq ft coverage each) for the floor above.
Open calculator with these dimensions →Crawlspace Insulation Guide
Crawlspace insulation prevents cold floors, reduces heating costs, and controls moisture. There are two approaches: insulating the floor above the crawlspace (traditional) or encapsulating the crawlspace walls (modern best practice). A 1,000 sq ft crawlspace is typical for a medium-sized home.
Two Approaches
| Method | R-Value | Cost (2026) | Pros |
|---|---|---|---|
| Floor batts (R-25) | R-25 | $500–$750 | Cheaper, simpler |
| Wall encapsulation (R-10 foam + vapor barrier) | R-10 | $1,500–$3,000 | Better moisture control, warmer floors |
Encapsulation vs. Traditional
Building science has shifted toward crawlspace encapsulation — sealing the crawlspace from the ground and insulating the walls rather than the floor. This approach treats the crawlspace as conditioned space, preventing moisture problems, pest entry, and floor temperature swings. The upfront cost is higher but prevents expensive moisture damage over time.
Pro Tips
- A vapor barrier is non-negotiable. Whether you insulate floor or walls, a 6-mil (or thicker) polyethylene vapor barrier on the ground prevents soil moisture from entering the space. Overlap seams 12 inches and tape.
- Never use faced fiberglass batts on crawlspace walls. The paper facing traps moisture against the foundation, promoting mold. Use unfaced batts or rigid foam board for walls.
- Vent or seal — pick one. Traditional vented crawlspaces use floor insulation and open vents. Encapsulated crawlspaces seal all vents and insulate walls. Mixing approaches causes moisture problems.
- Inspect for water intrusion first. No amount of insulation fixes a wet crawlspace. Address grading, gutters, and drainage before insulating.
Frequently Asked Questions
Should I insulate the crawlspace floor or walls?
Modern building science recommends encapsulating the crawlspace (insulating walls, sealing vents, installing vapor barrier). This approach provides better moisture control and floor comfort than traditional floor-joist insulation.
What R-value for crawlspace insulation?
R-25 for floor joists (traditional method) or R-10 rigid foam for encapsulated walls. In cold climates (zones 5+), increase to R-30 for floors or R-15 for walls.