Cost Estimators · Interior Work
Spray Foam Insulation Cost Per Sq Ft Calculator
Enter your area and instantly estimate spray foam insulation cost — open-cell or closed-cell.
Spray foam insulation is the premium choice when you need a complete air barrier alongside high R-value in a tight space. Closed-cell spray foam doubles as a vapour barrier and adds structural rigidity — making it ideal for rim joists, crawl spaces, and roof decking. But it costs 3–5× more per sq ft than blown-in. Use this calculator to see whether spray foam makes financial sense for your specific project.
Enter an area above to see your estimate
Using national average: $2–$8/sq ft
Estimates are based on national averages and are for planning purposes only. Actual costs vary by location, contractor, and material choice.
Example: 800 sq ft spray foam area
Area
800
sq ft
Low Estimate
$1,600
@ $2/sq ft
High Estimate
$6,400
@ $8/sq ft
Based on national average rates of $2–$8/sq ft. Actual costs will vary by location and contractor.
How much does spray foam insulation cost per square foot?
Open-cell spray foam costs $1.50–$4 per sq ft installed at standard depth (3.5 inches). Closed-cell spray foam runs $3–$8 per sq ft at standard depth (2 inches). Both are significantly more expensive than blown-in or batt insulation, but spray foam creates a complete air seal that no other insulation type can match. Federal tax credits of up to $1,200 per year apply to qualifying insulation improvements. For a full insulation type comparison, see our insulation cost per sq ft calculator.
Cost by project size
| Project size | Low estimate | High estimate |
|---|---|---|
| 200 sq ft (rim joists / crawl space) | $400 | $1,600 |
| 400 sq ft | $800 | $3,200 |
| 800 sq ft (attic rafter bays) | $1,600 | $6,400 |
| 1,200 sq ft | $2,400 | $9,600 |
| 1,600 sq ft (full attic roofline) | $3,200 | $12,800 |
Approximate 2026 US national averages at $2–$8/sq ft installed. Actual costs vary by location, contractor, and project complexity.
What affects interior work cost per square foot?
Open-cell vs closed-cell
Open-cell foam (0.5 lb density) expands to fill cavities and costs $1.50–$4/sq ft. It achieves R-3.6 per inch and is a good air barrier but not a vapour barrier. Closed-cell foam (2 lb density) costs $3–$8/sq ft, achieves R-6.5 per inch, and acts as both air and vapour barrier — the premium choice.
Application thickness
Closed-cell foam is typically applied at 2 inches (R-13) in wall cavities. Rim joists and crawl space walls often get 3 inches (R-20). Attic rafter bays get 5–6 inches for R-33 to R-39. Each additional inch of closed-cell adds roughly $1–$2/sq ft.
Application location
Rim joists and crawl space walls are the highest-value spray foam locations — they are the most air-leaky areas in most homes and small in area. Attic rooflines create conditioned attic space and protect HVAC equipment. Wall cavities are the most expensive application due to area.
Climate & vapour management
In cold climates (Zone 5+), closed-cell foam's vapour-barrier properties are important for wall assemblies — preventing moisture accumulation in the wall cavity. In warm climates, open-cell is often acceptable and significantly cheaper.
Installation precautions
Spray foam must be applied by trained professionals — improper mixing ratios or insufficient ventilation cause off-gassing and poor performance. Occupants should vacate during application and for 24 hours after. The foam must be covered with a thermal barrier (drywall) in finished spaces per fire code.
Tax credits & rebates
Federal tax credits of 30% (up to $1,200/year) apply to qualifying insulation improvements including spray foam under the Inflation Reduction Act. Many utilities offer additional rebates of $200–$500. Always confirm current credit limits with a tax professional before purchasing.
Frequently asked questions
How much does spray foam insulation cost per square foot?
Open-cell spray foam costs $1.50–$4 per sq ft installed at 3.5 inches. Closed-cell spray foam runs $3–$8 per sq ft at 2 inches. For an 800 sq ft attic roofline with closed-cell, expect $2,400–$6,400. Rim joist spray foam (typically 200–300 sq ft) costs $600–$2,400.
Is closed-cell or open-cell spray foam better?
Closed-cell foam is better when you need a vapour barrier, maximum R-value per inch, or structural rigidity (it adds 200–300% racking strength to walls). Open-cell is better when budget is the primary concern, in interior partitions where sound dampening matters, or in climates where vapour barriers are not required.
Where is spray foam insulation most cost-effective?
Rim joists (where the floor system meets the foundation) are the highest-value spray foam location — small area, big impact. Crawl space walls and basement band joists are similarly high-value. Attic rafter bays (creating a conditioned attic) are ideal when HVAC equipment is in the attic. Full wall cavity spray foam is the most expensive application.
How long does spray foam insulation last?
Spray foam insulation has an indefinite lifespan — it does not settle, compress, or degrade like fibreglass batts. Most manufacturers offer lifetime warranties. The foam itself should outlast the building if properly applied and protected from UV exposure (it degrades if left exposed to sunlight).
Can I spray foam over existing insulation?
No — spray foam must be applied to a clean substrate. Existing insulation must be removed before spray foam is applied. In attics being converted to conditioned space, existing attic floor insulation is removed before the rafter bays are sprayed. This increases project cost but the conditioned attic is significantly more energy-efficient.