Spray Foam Insulation Calculator
Enter your area and target R-value to calculate board feet of open-cell or closed-cell spray foam needed. Results update instantly.
Spray Foam Details
Open-Cell vs Closed-Cell at Your Target R-value
| Foam Type | R/inch | Thickness | Board Feet | Vapor barrier? |
|---|
Formula
additional_R = max(0, target_R − existing_R)
thickness_in = additional_R ÷ R_per_inch
board_feet = area_sqft × thickness_in
1 board foot (BF) = 1 sq ft at 1 inch thick = 1/12 cu ft
Related Calculators
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Frequently Asked Questions
One board foot (BF) equals 1 square foot of area at 1 inch thick (12" × 12" × 1"). To insulate 500 sq ft at 3 inches thick you need 500 × 3 = 1,500 board feet.
Open-cell spray foam delivers approximately R-3.7 per inch. Closed-cell delivers approximately R-6.5 per inch. Because closed-cell is denser and has higher R per inch, it reaches the same R-value at roughly half the thickness of open-cell.
DIY spray foam kits vary widely — common sizes range from 15 board feet (small crack-fill kits) to 600 board feet (large two-component kits). For large projects, professional contractors use drum or cylinder sets that yield 2,000–6,000+ board feet. Always check the specific kit's labeled yield.
Closed-cell spray foam at 2 inches or more acts as an effective vapor retarder (class II). Open-cell foam does not act as a vapor barrier. In cold climates, vapor control is an important part of attic and wall design — consult a building science professional if you are unsure.
Open-cell foam is commonly used to spray the underside of roof decking (creating a conditioned attic), not the attic floor. Closed-cell is often used on foundation walls, rim joists, and in crawl spaces. Application method and location significantly affect performance and code compliance — verify with a licensed contractor before proceeding.