Spray Foam Cost & Material Calculator
How to Calculate Spray Foam Insulation Needs
Estimating the cost of spray foam insulation requires understanding a unique unit of measurement called the "Board Foot." Unlike rolls of fiberglass that are sold by square footage, spray foam is sold by volume because the chemical expands when applied. This calculator helps you determine exactly how much material you need and estimates the cost based on current market rates.
What is a Board Foot?
A board foot is a volume measurement used specifically in the spray foam industry. It represents a square foot of area covered to a depth of exactly one inch.
- Formula: Area (sq. ft.) × Thickness (inches) = Board Feet
- Example: If you are insulating a 1,000 sq. ft. attic to a depth of 3 inches, you need 3,000 board feet of material.
Open Cell vs. Closed Cell Cost Factors
The "Price per Board Foot" input varies significantly depending on the type of foam you select:
- Open Cell Foam (Approx. $0.35 – $0.70 / bd ft): Less expensive and expands massively. It has a lower R-value per inch (around R-3.5) and is water-permeable. It is ideal for soundproofing and interior walls.
- Closed Cell Foam (Approx. $1.00 – $1.60 / bd ft): More expensive, dense, and rigid. It acts as a vapor barrier and adds structural strength. It has a high R-value per inch (around R-6.0 to R-7.0), making it perfect for shallow wall cavities and roofs.
Why Account for Waste?
In spray foam applications, achieving 100% yield is rare due to factors like temperature, humidity, and overspray. Additionally, foam often expands beyond the studs and must be trimmed back (scarfed) to install drywall, resulting in waste. Professionals typically calculate a 10% to 15% waste factor to ensure they have enough chemical on-site to complete the job without interruption.
Understanding R-Value Requirements
Your local building code will dictate the required R-Value for different parts of your home. To achieve a specific R-Value, you adjust the thickness of the foam. For example, if your zone requires R-38 for an attic ceiling and you are using closed cell foam (R-7 per inch), you would need approximately 5.5 inches of thickness.