Enter total wall sq ft (height x perimeter minus openings)
Spray Foam Estimate
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| Property | Open-Cell | Closed-Cell |
|---|---|---|
| R-Value per Inch | 3.7 | 6.5 |
| Density | 0.5 lb/cf | 2.0 lb/cf |
| Vapor Barrier | No | Yes (at 1.5"+) |
| Air Barrier | Yes | Yes |
| Structural Strength | None | Adds racking strength |
| Cost (installed) | $1.00-$2.00/sf | $2.00-$5.00/sf |
| Best For | Walls, attics | Crawlspaces, rim joists |
Spray Foam Insulation Cost & Specification Guide
Open-cell vs. closed-cell comparison, board foot calculations, code requirements, and pricing data for spray foam insulation projects.
How Much Does Spray Foam Insulation Cost?
Open-cell spray foam costs $1.00-$2.00 per square foot installed, while closed-cell runs $2.00-$5.00 per square foot. The per-board-foot cost (1 sq ft at 1 inch thick) is $0.35-$0.65 for open-cell and $1.00-$2.00 for closed-cell.
- Open-cell (0.5 lb density): $1.00-$2.00/sq ft installed at typical wall thickness
- Closed-cell (2.0 lb density): $2.00-$5.00/sq ft installed at typical wall thickness
- Minimum job charge: Most spray foam contractors have a $1,500-$3,000 minimum, even for small areas
- Rim joist spray (common add-on): $2.00-$4.00/linear foot
Prices vary by region, thickness required, and access difficulty. Cathedral ceilings and tight crawlspaces cost 15-25% more than open-access attics.
Key Takeaways
- Open-cell: $1.00-$2.00/sf installed (walls/attics)
- Closed-cell: $2.00-$5.00/sf installed (crawl/rim joists)
- Most contractors have a $1,500-$3,000 minimum job charge
Open-Cell vs. Closed-Cell Spray Foam
Closed-cell foam delivers R-6.5 per inch and acts as a vapor barrier, while open-cell provides R-3.7 per inch and allows the wall to dry. The right choice depends on your climate, location in the building, and moisture exposure.
- Open-cell: R-3.7/in, 0.5 lb/cf density, excellent air seal, allows moisture to pass through, ideal for walls and attic slopes in moderate climates
- Closed-cell: R-6.5/in, 2.0 lb/cf density, air + vapor barrier, adds structural racking strength, required for below-grade and high-moisture areas
- When to use open-cell: Interior walls, attics in climate zones 1-4, where drying potential matters
- When to use closed-cell: Crawlspaces, rim joists, exterior sheathing, flood zones, and cold climates (zones 5+)
Many contractors use a hybrid approach: 2 inches of closed-cell for vapor barrier, then fill the rest of the cavity with open-cell. This cuts cost by 20-30% compared to all closed-cell while still meeting code.
Key Takeaways
- Open-cell: R-3.7/in, breathable, lower cost
- Closed-cell: R-6.5/in, vapor barrier, structural
- Hybrid approach (2" closed + open fill) saves 20-30%
How Board Feet Are Calculated
One board foot of spray foam covers 1 square foot at 1 inch thick. Total board feet = area (sq ft) x thickness (inches). This is how spray foam contractors price and measure every job.
- Example: 1,000 sq ft wall at 3.5 inches thick = 3,500 board feet
- Waste/overspray factor: Add 10-15% for overspray, trimming, and corners
- Yield per kit: A standard 600 board-foot kit covers roughly 600 sq ft at 1 inch, or 200 sq ft at 3 inches
- Temperature affects yield: Cold substrate or ambient temps below 60F reduce chemical yield by 10-20%
Key Takeaways
- 1 board foot = 1 sq ft x 1 inch thick
- Add 10-15% for overspray and trimming waste
- Cold temperatures reduce yield by 10-20%
Building Code Requirements for Spray Foam
IRC requires a thermal barrier (1/2" drywall) over spray foam in occupied spaces. Some jurisdictions accept an intumescent coating as an alternative. Always verify local code before skipping drywall.
- Thermal barrier: Required in all occupied areas per IRC R316.4. 15-minute fire rating, typically 1/2" gypsum board
- Ignition barrier: Attics and crawlspaces may use a lesser ignition barrier if not occupied
- Vapor retarder: Closed-cell foam at 1.5"+ qualifies as a Class II vapor retarder per IRC Table R702.7.1
- Flash-and-batt: Many codes accept 2" closed-cell flash coat + fiberglass batts to fill the cavity. Meets code, saves money
Key Takeaways
- Thermal barrier (drywall) required over foam in living spaces
- Closed-cell at 1.5"+ acts as Class II vapor retarder
- Flash-and-batt (2" closed + batts) is a code-compliant cost saver
How to Use This Calculator
Select your application
Choose where spray foam will be installed: walls, attic, crawlspace, rim joists, or roof deck. The calculator recommends open-cell or closed-cell based on the application.
Enter the area in square feet
Measure the total square footage to be sprayed. For walls, multiply perimeter length by wall height and subtract door and window openings.
Choose open-cell or closed-cell foam
Open-cell (R-3.7/in) costs less and works well in walls and attics. Closed-cell (R-6.5/in) acts as a vapor barrier and adds structural strength for crawlspaces and rim joists.
Set your target R-value
The calculator determines the thickness needed to hit your target R-value. Higher R-values need thicker foam but improve energy performance.
Review board feet and cost breakdown
See the total board feet required (area x thickness), plus a material and labor cost estimate with a built-in waste factor for overspray.
Spray Foam Calculation Formulas
Thickness (in) = Target R-Value / R-per-Inch
Board Feet = Area (sq ft) x Thickness (in)
Total Board Feet = Board Feet x (1 + Waste %)
Material Cost = Total Board Feet x Cost per Board Foot
Labor Cost = Total Board Feet x Labor Rate per Board Foot
Total Installed Cost = Material + LaborWhere:
- R-per-Inch
- = Open-cell: 3.7, Closed-cell: 6.5
- Board Foot
- = 1 sq ft of coverage at 1 inch thick
- Waste Factor
- = Typically 10-15% for overspray and trimming
Spray Foam Insulation Cost Table (2026)
| Foam Type | R-Value/Inch | Installed Cost/SF | Best Application |
|---|---|---|---|
| Open-Cell (0.5 lb) | R-3.7 | $1.00 - $2.00 | Walls, attics |
| Closed-Cell (2 lb) | R-6.5 | $2.00 - $5.00 | Crawlspaces, rim joists, basements |
| Hybrid (2" CC + OC fill) | R-4.5 avg | $1.50 - $3.00 | Walls where vapor barrier needed |
Prices reflect national averages for professional installation. Material and labor included. Minimum job charges of $1,500-$3,000 are common. Source: Angi 2026 insulation cost guide. Last updated: April 2026.
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Frequently Asked Questions
How much does spray foam insulation cost per square foot?
Open-cell spray foam costs $1.00 to $2.00 per square foot installed at typical wall thickness. Closed-cell runs $2.00 to $5.00 per square foot installed. Most spray foam contractors have a $1,500 to $3,000 minimum job charge, so small projects cost more per square foot.
What is a board foot of spray foam?
One board foot equals 1 square foot of coverage at 1 inch thick. A 1,000 sq ft wall sprayed 3.5 inches thick = 3,500 board feet. Spray foam contractors price by the board foot, typically $0.35-$0.65/bf for open-cell and $1.00-$2.00/bf for closed-cell.
Should I use open-cell or closed-cell spray foam?
Use open-cell for interior walls and attics where moisture needs to dry through the assembly. Use closed-cell for crawlspaces, rim joists, basement walls, and flood zones where a vapor barrier and moisture resistance are critical. Closed-cell also adds structural racking strength to wall framing.
How thick does spray foam need to be?
Thickness depends on the target R-value. Open-cell at R-3.7/in needs 3.5 inches for R-13 (2x4 walls) and 5.1 inches for R-19 (2x6 walls). Closed-cell at R-6.5/in needs only 2 inches for R-13 and 3 inches for R-19. Attics typically require 8-10+ inches of open-cell or 5-6 inches of closed-cell.
Can I spray foam insulation myself (DIY)?
DIY spray foam kits are available in the 200-600 board foot range for $300-$700 per kit. They work for small jobs like rim joists, band boards, and gaps. For anything larger than 200 sq ft, professional installation is strongly recommended. The equipment, chemical handling, and coverage consistency require training. A bad spray job can trap moisture, cause off-gassing, or require expensive removal.
Does spray foam insulation pay for itself?
Most homeowners see a 25-40% reduction in heating and cooling bills after spray foam installation, depending on the home's existing insulation and air leakage. In cold climates, payback on a full-house spray foam job is typically 5-8 years through energy savings alone. The added benefit of air sealing (spray foam is both insulation and air barrier) makes it more effective than batts at the same R-value.
How much overspray waste should I plan for?
Professional spray foam contractors typically factor 10-15% overspray and waste into their estimates. Tight spaces, irregular framing, and cold temperatures can push waste closer to 15-20%. Our calculator defaults to 10% waste, which matches typical residential conditions.
Is spray foam better than fiberglass batts?
Spray foam outperforms fiberglass in air sealing, moisture control, and R-value per inch. Fiberglass batts provide R-3.2/in and leave gaps at framing, wiring, and plumbing. Spray foam fills every void and acts as an air barrier, which fiberglass cannot do. The tradeoff is cost: spray foam costs 2-4x more than batts installed. For retrofit jobs where you can't access wall cavities, spray foam is often the only practical option.
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