Spray foam insulation cost: per square foot, for attics and crawl spaces, by state
1,000 sq ft, a mid-size attic roof deck: about $4,050 to $5,700, typically $4,600. That's 6 inches of open cell spray foam sprayed on, plus the contractor's overhead, profit and sales tax. Everything in, it runs $4.00 to $5.75 a sq ft. Removing old insulation, a thermal or ignition barrier over the foam, and air sealing elsewhere are extra.
Anthony Hicks30+ years in construction. Updated November 5, 2026.
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What it costs
| Job | Cost |
|---|---|
| 500 sq ft, a small attic or crawl space | $2,000 to $2,850 |
| 1,000 sq ft, a mid-size attic roof deck | $4,050 to $5,700 |
| 1,500 sq ft, a large attic roof deck | $6,100 to $8,600 |
About $4.00 to $5.75 a sq ft, everything in.
Totals include the contractor's overhead and profit (20%) and the state's average sales tax. Prices as of November 2026.
What’s in these numbers
Each total is a typical job, priced the way a contractor’s estimate is priced:
- Open cell spray foam, 6 inches thick, sprayed on the area shown: the underside of a roof deck, or a crawl space’s walls.
- Overhead and profit: 20%, the standard markup on a contractor’s estimate.
- Sales tax on the materials, at the state’s average rate.
Not in them: taking out old insulation, the thermal or ignition barrier the code may call for over the foam, closed cell foam, sealing ducts and other openings, and permits.
What the code says about foam
Spray foam is a foam plastic in the building code, and it can’t be left bare inside the house:
- Living space: foam is covered by a thermal barrier, such as 1/2 inch gypsum wallboard (IRC R316.4).
- Attics and crawl spaces entered only for repairs or maintenance: a lighter ignition barrier can do instead, such as 1 1/2 inches of mineral fiber insulation or 3/8 inch gypsum board, or none for a foam tested for it (R316.5.3, R316.5.4).
- Unvented attics: foam sprayed under the roof deck can make the attic part of the house’s insulated space, allowed when the code’s conditions for unvented attics are met (R806.5).
What moves the price
- Open or closed cell. Closed cell foam is denser and costs more per inch than open cell.
- Thickness. More inches cost more; the R-value the code calls for in your climate sets how many.
- Getting there. Tight attics and crawl spaces take longer.
- Prep. Old insulation taken out, and a barrier put up over the foam, add lines of their own.
- Where you live. Pick your state in the box above.
Common questions
How much does spray foam cost per square foot?
$4.00 to $5.75 a sq ft for 6 inches of open cell foam, with overhead, profit and sales tax.
How much to spray foam an attic?
About $4,050 to $5,700 for 1,000 square feet of roof deck, typically $4,600.
How much for a small attic or crawl space?
About $2,000 to $2,850 for 500 square feet.
Is spray foam better than blown-in insulation?
They do different jobs. Blown-in insulation lies on the attic floor in a vented attic; spray foam is sprayed onto the roof deck or walls and fills the gaps there. The blown-in insulation cost guide prices the attic floor.