Methodology & Pricing Sources

Every number the calculator shows can be traced to the steps below. Estimates are for planning, not quotes.

1. Spray area

You describe a rectangular building by length, width, wall height and roof pitch (rise per 12 of run). From those we compute each surface:

• Long walls = 2 × length × wall height
• End walls = 2 × width × wall height
• Gable triangles = 2 × ½ × width × ridge rise, where ridge rise = (width ÷ 2) × (pitch ÷ 12)
• Roof deck = 2 × length × slope length, where slope length = √((width ÷ 2)² + ridge rise²)
• Floor / ceiling = length × width

Doors and windows you add are subtracted from the wall they sit on (standard door 3 × 6.67 ft, garage door 9 × 7 ft, window 3 × 4 ft). The spray area is the sum of the surfaces you select.

2. Board feet

One board foot is one square foot sprayed one inch thick. Board feet = spray area × thickness (in) × waste factor. We use a waste factor of 1.10 (+10%) for overspray and cuts.

3. R-value

R-value = thickness × R per inch: 3.7 per inch for open-cell and 6.5 per inch for closed-cell foam. These are typical manufacturer-range figures; check the data sheet of the product you buy.

4. Price

• The professional range is the installed price (material, labor and equipment) per board foot. The estimate is board feet × the low and high rates above. Most installers also charge a minimum per job, so it is never below $1,500.
• The DIY figure comes from retail kit prices: 200 board ft closed-cell kits: Froth-Pak 200 $419, Touch n Seal 200 $417.35, Tiger Foam Fast Rise 200 $385 (median $417 / 200 bd ft); 600+ board ft kits: Tiger Foam 600 $785, Froth-Pak 630 $979-$1,079 (median about $1.55 / bd ft). DIY costs cover materials only, not safety gear, equipment or your time.
• These are national planning ranges. They can be well off for your area, job size or access. Published prices vary a lot: several sites quote $0.44–$0.65 (open-cell) and $1.00–$1.50 (closed-cell) per board foot, but those are material-only figures, not installed prices.

Where the numbers come from

• Professional installed price: the average of the low and high ends of two published 2026 installed-price ranges: HomeAdvisor (updated June 2026: open-cell $0.60–$1.60, closed-cell $1.30–$3.10 per board foot) and insulationrvalues.com (updated May 2026: open-cell $0.35–$0.55, closed-cell $1.00–$2.50). Averaged, that gives the open-cell and closed-cell ranges in the table.
• Material-only reference: Fixr (January 2025) lists $0.44–$0.65 (open-cell) and $1.00–$1.50 (closed-cell) per board foot as material only. We do not use it as an installed price.
• Labor share: insulationrvalues.com puts materials at 40–50% of the installed price and labor plus equipment at 50–60%. The cost breakdown bar on the results page uses 45% / 55%.
• Minimum job charge: typically $1,000–$2,000 (insulationrvalues.com); we use the midpoint. Some contractors set it higher, for example $3,000 at RetroFoam of Michigan.
• DIY kits: retail prices from RetroFoam's 2026 kit price list (Froth-Pak 200 at $419, Tiger Foam Fast Rise 200 at $385, Tiger Foam 600 at $785, Froth-Pak 630 at $979–$1,079) and Conservation Mart (Touch n Seal 200 at $417.35).
• Removing old insulation: Dropcurb (April 2026): $1–$1.50 per sq ft for blown-in and $1–$2 for batts.

Retail and installer prices change, and these sources disagree with each other. We re-check them periodically, and the date below shows the last review.

Price data was last reviewed on October 7, 2026.

5. Climate-based thickness suggestions

The foam page can suggest a thickness from your state's IECC climate zone. It divides a target R-value for that zone (wall or attic) by the foam's R per inch and rounds up to the nearest half inch. Local code and the product's approvals take precedence; confirm with your building department or installer.

Limits

• The model is a rectangular building with a gable or flat roof. Complex shapes should be split into several estimates or quoted on site.
• The estimate does not include removing old insulation (typically $1.00 - $2.00 per sq ft), drilling and filling existing closed walls (typically $1.00 - $2.00 per sq ft), repairs, ventilation changes, permits or taxes. Add these when you compare quotes.

Found a mistake? Tell us.