Spray Foam Insulation Calculator
Project Estimates
Total Area: 0 sq. ft.
Board Feet Needed: 0 bd. ft.
Total R-Value: 0
Estimated Cost: $0.00
*Cost is based on market averages: $0.55/bd ft for Open Cell and $1.25/bd ft for Closed Cell.
How to Calculate Spray Foam Requirements
Planning a spray foam insulation project requires understanding a unique unit of measurement: the Board Foot. Unlike standard square footage used for paint or flooring, spray foam is measured by volume. One board foot represents a surface area of one square foot with a thickness of one inch.
The Formula for Board Feet
To determine how much material your project requires, use the following calculation:
(Length × Height) × Thickness in Inches = Board Feet
For example, if you have a 100-square-foot wall and you want to apply 3 inches of foam, you need 300 board feet of material. It is always recommended to add a 10% to 15% waste factor to account for "flash" (the first thin layer), uneven substrates, and trimming excess foam flush with studs.
Open Cell vs. Closed Cell Insulation
When calculating your needs, the type of foam dictates both the performance (R-value) and the cost:
- Open Cell Foam: Typically has an R-value of 3.5 to 3.8 per inch. It is lighter, more flexible, and acts as an excellent sound barrier. It is generally less expensive, averaging $0.45 to $0.65 per board foot.
- Closed Cell Foam: Offers a much higher R-value of 6.0 to 7.0 per inch. It is dense, rigid, and acts as a moisture barrier. Because of its density, it is more expensive, typically ranging from $1.00 to $1.50 per board foot.
Practical Example Calculation
Suppose you are insulating a 20′ x 10′ garage wall (200 sq. ft.) with 2 inches of Closed Cell foam:
- Square Footage: 20 x 10 = 200 sq. ft.
- Board Footage: 200 sq. ft. x 2 inches = 400 board feet.
- With Waste (10%): 400 + 40 = 440 board feet.
- Total R-Value: 2 inches x 6.5 = R-13.