How much does spray foam insulation cost?

It depends on your quoted price and the depth. A 500 ft² wall at 2" and $1.20/board-foot is about $1,320 with 10% contingency; a 1,000 ft² attic at $2.50/ft² is about $2,750. Enter your own price in the spray foam cost tool.

Is spray foam priced by the board-foot or the square foot?

Both are used. Material is sold by the board-foot (1 ft² at 1"); contractors often quote installed by the square foot at a set depth. board-feet = area × thickness ties the two together.

Why is closed-cell more expensive but sometimes the cheaper job?

Closed-cell costs more per board-foot but hits the same R in about half the depth (~6.5 vs ~3.6 R/inch), so you spray far fewer board-feet. Run both in the open- vs closed-cell calculator.

Does the quote include the ignition barrier?

Not always — ask. Exposed foam usually needs a code-required thermal or ignition barrier, which can be a separate line item. The requirement is set by the manufacturer and your local code.

Is spray foam worth the extra cost?

Where you're buying more than R — rim joists, crawlspace/basement walls, cathedral ceilings, bonus rooms — closed-cell earns its premium by air-sealing and controlling vapor in one pass. On an open, accessible attic floor a cheap blow to R-49 is usually just as effective for far less. Match the foam to the problem, not the pitch.

Spray foam insulation cost guide (attic, walls, board-feet)

Spray foam is the priciest insulation per square foot — and often the highest-performing. Price it two ways: by board-foot (the unit foam is sold in) or by square foot at a depth. Both run on your quoted price.

By Francesco Zinghinì

Two ways to price foam

By board-foot: total = (board-feet × your $/board-foot + labor − discount) × (1 + contingency). By area: total = area × your $/ft² at the depth/R × (1 + contingency). Board-feet = area × thickness, so the two agree when you convert. Price it in the spray foam insulation cost tool or the attic / wall cost tool.

Worked example: by board-foot

A 500 ft² wall at 2 inches = 1,000 board-feet. At $1.20/board-foot, no separate labor line, 10% contingency: (1,000 × 1.20 + 0) × 1.10 = 1,200 × 1.10 = $1,320. Get board-feet first in the board-feet calculator, then drop it into the cost tool.

Worked example: by area (attic)

An attic of 1,000 ft² quoted at $2.50/ft² installed, 10% contingency: 1,000 × 2.50 = 2,500; × 1.10 = $2,750. By-area pricing bakes the depth and labor into the $/ft², so it's the easy way to sanity-check a contractor line.

Open vs closed cell drives the price

Closed-cell costs more per board-foot and needs less depth per R (~6.5 R/inch); open-cell is cheaper per board-foot but you spray nearly twice the board-feet for the same R (~3.6 R/inch). So the cheaper-per-unit foam isn't automatically the cheaper job. Labeled installed bands: open-cell ~$1.00–$2.50/ft², closed-cell ~$1.50–$4.50/ft². Compare board-feet and cost side by side in the open- vs closed-cell calculator.

Job	Formula	Estimate
500 ft² wall, 2", $1.20/bd-ft	1,000 bd-ft × $1.20 × 1.10	~$1,320
1,000 ft² attic, $2.50/ft²	1,000 × $2.50 × 1.10	~$2,750

What drives the quote up (and what to check)

Depth/R: more inches = more board-feet = more cost, linearly. Confirm the sprayed thickness in the quote.
Access and prep: tight crawlspaces, masking, and removal of old insulation all add labor.
Ignition/thermal barrier: exposed foam usually needs a code-required cover — that can be a separate line item.
Small-job minimums: foam rigs have a setup cost; tiny jobs carry a premium per square foot.

Estimate, not a bid — and not a design

Reading a foam quote line by line

Foam quotes vary more than any other insulation because the depth is a choice. Pin down four things: the foam type (open vs closed), the sprayed thickness or target R (this drives board-feet and therefore cost — get it in writing), the area, and what's in the labor line (prep, masking, old-insulation removal, the ignition/thermal barrier). Convert to a check number: quote ÷ area = $/ft², or quote ÷ board-feet = $/board-foot. A 1,500 ft² attic foamed to R-38 closed-cell is ~8,770 board-feet; a $12,000 quote is ~$1.37/board-foot — reasonable for closed-cell. If a quote is dramatically under band, ask what depth they're actually spraying; a thin pass hits a price, not an R.

Where foam earns its premium — and where it doesn't

Closed-cell is worth the money where you're buying more than R: rim joists and crawlspace/basement walls (air seal + vapor control + R in one pass), cathedral ceilings with no room for vented depth, and bonus rooms over garages. It's overkill where a cheap batt or blow does the same job — an open, accessible attic floor is almost always cheaper and just as effective in loose-fill to R-49. Open-cell shines indoors for sound and for filling irregular framing where you don't need the vapor performance. Match the foam to the problem, not to the sales pitch.

Budget levers you actually control

Depth: every extra inch is more board-feet, linearly. Spec the R you need, not the R that sounds impressive.
Hybrid assemblies: a thin closed-cell flash coat for the air/vapor seal plus a cheaper fill (batt or blown) over it often beats all-foam on cost for the same R.
Access & prep: clear the space and remove old insulation yourself where safe — foam labor is expensive.
Job size: rigs have a setup cost, so tiny jobs carry a per-ft² premium; bundle small foam jobs together.

Quick numbers to leave with

By board-foot: (board-feet × $/bd-ft + labor − discount) × (1 + contingency). 1,000 bd-ft at $1.20 + 10% = ~$1,320.
By area: area × $/ft² × (1 + contingency). 1,000 ft² attic at $2.50 + 10% = ~$2,750.
Check numbers: quote ÷ area = $/ft²; quote ÷ board-feet = $/bd-ft.
Bands: open-cell ~$1.00–$2.50/ft², closed-cell ~$1.50–$4.50/ft² installed.
Cheapest same-R fix is often a flash-and-batt hybrid, not all-foam.

These tools compare your own numbers; they don't issue a bid. Get itemized written quotes from licensed, insured contractors. And spray foam has real code and safety detailing — ignition/thermal barriers, vapor control, combustion-air safety for nearby appliances — that's set by the product data sheet and your local code, not this calculator. Price the material, then let a pro handle the detailing.