Spray foam insulation cost calculator.
Zone in, inches checked, board feet priced at your quote.
Spray foam is priced by the board foot: one square foot, one inch thick. This calculator takes your climate zone, proposes the ENERGY STAR R-value for each surface, turns it into inches of open- or closed-cell foam, checks those inches against your studs or rafters, and multiplies the board feet by your own quote.
0302 / Estimate
- Open cell
- 5,280 BF
- Closed cell
- 16,000 BF
- Foam at your quotes
- Enter a $/board foot quote
- Thermal barrier area
- 960 sq ft of 1/2 in gypsum or equal
- Ignition barrier area
- 2,000 sq ft
- Barrier at your quotes
- Not priced
- Estimate total
- —
- Framing check
- 1 of 3 overflow
- Surface sprayed
- 2,960 sq ft
Each $0.10 per board foot of quote moves the open-cell line by $528.00 and the closed-cell line by $1,600.00.
0203 / Foam against framing
Zone 5, ENERGY STAR retrofit levels: attic R60 (none there yet) or R49 (over 3–4 in), floor R30, basement or crawlspace wall R19 batt. 2021 IECC ceiling, as DOE summarizes it: R-60.
B · Roofline, underside of the roof deck: R-60 at R-6 per inch needs 10.00 in of foam, 0.75 in deeper than the 2×10, 9-1/4 in framing. Flush with the framing it reaches R-55.5. Deeper framing, furring strips or rigid insulation outside the framing change that; trimming the foam flush does not.
Open cell and closed cell have no quote per board foot yet, so no dollar total is shown. Calculiva publishes no foam price.
The thermal and ignition barrier areas have no quote and are left out of the total, not counted as free.
Surface by surface, inch by inch
| Surface | Area | Foam | Target | Thickness | Framing | Board feet | Cost |
|---|---|---|---|---|---|---|---|
| A · Above-grade wall | 960 sq ft | Open cell · R-3.6/in | R-19.8 · cavity filled | 5.50 in | fits 2×6, 5-1/2 in | 5,280 | — |
| B · Roofline, underside of the roof deck | 1,200 sq ft | Closed cell · R-6/in | R-60 · ENERGY STAR | 10.00 in | 0.75 in over 2×10, 9-1/4 in | 12,000 | — |
| C · Floor over a crawlspace or garage | 800 sq ft | Closed cell · R-6/in | R-30 · ENERGY STAR | 5.00 in | fits 2×10, 9-1/4 in | 4,000 | — |
The barrier lines
| Line | Surfaces | Area | Your quote | Amount |
|---|---|---|---|---|
| Thermal barrier (R316.4) | A | 960 sq ft | — | not priced |
| Ignition barrier (R316.5.3, R316.5.4) | B, C | 2,000 sq ft | — | not priced |
A wall that will be finished with 1/2-inch gypsum wallboard anyway already carries its thermal barrier; leave its quote blank and the line stays a reminder rather than a second charge.
What owners reported spending on insulation
| Area | Projects sampled | 25th percentile | Median | 75th percentile | Done by the owner |
|---|---|---|---|---|---|
| United States | 888 | $500 | $1,500 | $2,900 | 44.7 % |
| Northeast | 177 | $500 | $1,500 | $2,900 | 41.4 % |
| Midwest | 189 | $360 | $1,000 | $2,500 | 51.5 % |
| South | 294 | $510 | $1,500 | $3,000 | 44.5 % |
| West | 228 | $500 | $1,700 | $3,000 | 39.3 % |
Enter a quote per board foot for every foam used to place your total among what Midwest owners reported spending (AHS 2023).
These are what households said they spent on a job the survey files as insulation, in the two years before the interview, with no record of the material, the thickness or the size of the house. Almost half were do-it-yourself jobs, whose cost usually leaves out labor. The table is the honest edge of what is measured: no public survey publishes what spray foam alone costs per board foot.
The ENERGY STAR levels the zone selector reads
| Zone | Attic, none there yet | Attic, 3–4 in there | Floor | 2021 IECC ceiling, per DOE |
|---|---|---|---|---|
| 1 | R30 | R25 | R13 | not quoted |
| 2 | R49 | R38 | R13 | R-49 |
| 3 | R49 | R38 | R19 | R-49 |
| 4A and 4B | R60 | R49 | R19 | R-60 |
| 6, 5, and 4C | R60 | R49 | R30 | R-60 |
| 7 and 8 | R60 | R49 | R38 | R-60 |
For basement and crawlspace walls ENERGY STAR offers a batt alternative of R13 in zones 3, 4A and 4B and R19 in 4C and 5 to 8; it lists nothing for zones 1 and 2. Foam or batts go on the inside face of that wall; the outside face, from finished grade down, is what the foundation waterproofing estimate measures. For walls above ground it only describes sheathing added under new siding, so the calculator asks for your own wall target or fills the cavity.
Why R-60 does not fit in a 2×10 rafter
The worked example is a zone 5 house with three surfaces. The walls, 120 feet of them at 8 feet high, are 2×6 studs filled flush with open-cell foam. The roofline is 1,200 square feet of 2×10 rafters sprayed with closed cell to the ENERGY STAR attic level. The floor over the crawlspace, 40 by 20 feet, takes closed cell to the ENERGY STAR floor level between 2×10 joists.
Zone 5 sits in the row ENERGY STAR labels “6, 5, and 4C”: R60 for an attic with no insulation, R30 for a floor. At the typical R-6 per inch of the DOE guide, R-60 is 10 inches of closed cell. A nominal 10-inch width is dressed to 9-1/4 inches in the softwood lumber standard, so the target overflows the rafter by 3/4 inch, and a flush roofline stops at R-55.5. In open cell at R-3.6 per inch the same target is 16.67 inches, and the flush rafter holds R-33.3. No contractor price changes that geometry; deeper rafters, furring strips or rigid board outside the deck do.
The floor fits with room to spare: R-30 is 5 inches of closed cell in a 9-1/4-inch joist. The walls have no ENERGY STAR cavity level, so they are filled: 5-1/2 inches of open cell in a 2×6 is R-19.8.
Board feet are the quantity every quote multiplies
A board foot is 144 cubic inches, one square foot one inch deep. The walls are 960 square feet at 5.5 inches, 5,280 board feet of open cell. The roofline is 1,200 square feet at 10 inches, 12,000 board feet, and the floor 800 square feet at 5 inches, 4,000: together 16,000 board feet of closed cell and 21,280 for the job.
Those quantities make quotes comparable. Every $0.10 per board foot of difference between two closed-cell bids moves this job by $1,600; on the open-cell walls it moves it by $528. A bid quoted per square foot only becomes comparable once it states its inches, and the calculator prices the inches your target needs, not the ones a bid assumed.
Where the targets come from, and what they are not
The zone selector reads the ENERGY STAR table of recommended levels for retrofitting existing wood-framed buildings, which says it is based on the 2021 IECC, Table R402.1.3. It is a recommendation for existing homes, not a code minimum, and its attic columns are the insulation to add. The only code figures shown are the ceiling values DOE’s Building Energy Codes Program gives for the 2021 IECC: R-49 in zones 2 and 3, R-60 in zones 4 to 8. When a ceiling surface is set below them, the warning names the gap and leaves the decision to the building department.
R per inch is an editable field because the figures are typical, not guaranteed. The DOE guide gives about 3.6 for open-cell foam of roughly half a pound per cubic foot and 6 for typical closed-cell foam at 2 pounds, with an aged 6.1 in its property table, “variable within range”. A data sheet showing a different aged R-value replaces the default, and the thickness and board feet follow.
The barrier is a line on the bill
Foam plastic is combustible. Under section R316.4 of the 2021 IRC, read in Seattle’s adoption, it must be separated from the interior by 1/2-inch gypsum wallboard, 23/32-inch wood structural panel or a material that passes the two NFPA 275 fire tests. Sections R316.5.3 and R316.5.4 relax that in an attic or crawlspace entered only for repairs or maintenance, where an ignition barrier such as 1-1/2 inches of mineral fiber, 1/4-inch wood structural panel or 3/8-inch gypsum board can do, or none when the foam itself has been tested under R316.6. In the example, 960 square feet of wall need the thermal barrier and 2,000 square feet of roofline and crawlspace need the ignition line. The DOE guide says the same in substance: a 15-minute thermal barrier in habitable space.
The spending check, read with its limits
The total lands in the survey table once both foams are priced. Read it as a scale, not a verdict: a foam bill for the example’s 21,280 board feet passes the national median of $1,500 at any quote above 7.0 cents per board foot, and the 75th percentile of $2,900 above 13.6 cents; in the Midwest the 75th percentile is $2,500. Unless the quote is a few cents per board foot, a three-surface foam job of this size sits above most of the insulation projects owners described.
On 11 October 2026, the five estimators ranking first for this search were read one by one. None sets an R-value from a climate zone, none mentions a thermal or ignition barrier, and none cites a survey of what owners spend. They multiply an area by a thickness and a price.
Rounding and unit rules are set out in how Calculiva calculates; the exact wording behind each figure is on the four public sources and the survey listed beside this section.
Spray foam questions, answered in board feet
How much does it cost to spray foam 1,500 square feet?
The square feet do not set the bill on their own; the thickness does. Spray foam is sold by the board foot, square feet times inches, so 1,500 square feet sprayed 3 inches deep is 4,500 board feet and 5.5 inches deep is 8,250. Multiply by the quote per board foot you were given. For scale, the median insulation project owners reported in the 2023 American Housing Survey came to $1,500, all insulation types and do-it-yourself jobs included.
What would it cost to spray foam a 20x20 garage?
Measure the surfaces, not the slab. A 20 by 20 garage with 8-foot walls has 640 square feet of wall before the doors are taken out, plus 400 square feet of ceiling, or more if you spray along a sloped roof. Enter walls and roof as separate surfaces with their framing and read the board feet. Then keep the barrier line: foam left exposed inside the building falls under the thermal barrier rule of IRC R316.4 unless your building department accepts a tested alternative.
How much does it cost to spray foam a 40x60 shop?
Start from the shell. A 40 by 60 building has 200 feet of perimeter, so every foot of eave height adds 200 square feet of wall, and the roof covers at least 2,400 square feet, more along the slope. Type the slope length times the building length as the roof area; this page applies no pitch factor. At 2 inches of foam, every 1,000 square feet is 2,000 board feet to multiply by your quote.
What does spray foam cost for a 2,000-square-foot house?
The 2,000 square feet describe the floor plan, while the foam goes on walls, a roofline, an attic floor or a floor over a crawlspace, and their area is something else. In the worked example three surfaces add up to 2,960 square feet and 21,280 board feet. Measure each surface, let the zone set its target, and keep only the thickness its framing can hold.
Why is there no spray foam cost per square foot here?
Because a square foot of foam has no fixed size. One square foot at R-30 in closed cell, 5 inches at the typical R-6 per inch, is 5 board feet; the same square foot sprayed 2 inches deep is 2. A price per square foot hides a thickness inside it. Ask for the inches and the price per board foot: price per square foot equals price per board foot times inches.
Can I enter square feet instead of length and height?
Yes. Switch a surface to a known area and type the square feet from a roof plan or a contractor’s takeoff. The framing size and the target still apply, so the cavity check, the barrier line and the board feet work exactly as they do with dimensions.
What do households actually spend on an insulation project?
The 2023 American Housing Survey sampled 888 insulation projects reported by owner-occupants: a median of $1,500, a quarter under $500 and a quarter over $2,900, with 44.7 percent done by the owners themselves. The survey records neither the size of the house nor the type of insulation, so it is a reality check on a budget, not a spray foam price.
Can I use a contractor’s per-square-foot quote?
Convert it first. Divide the quoted price per square foot by the inches the contractor intends to spray and you have their price per board foot. Enter that, and any surface where your target R-value takes more inches than the quote assumed shows the difference as extra board feet instead of hiding it.
How many board feet does 1,200 square feet take?
Square feet times inches. The worked roofline is 1,200 square feet: R-60 in closed cell at R-6 per inch is 10 inches and 12,000 board feet, and in open cell at R-3.6 per inch it is 16.67 inches and 20,000 board feet. Filling 2x10 rafters flush, 9-1/4 inches deep, is 11,100 board feet whichever foam you choose.
Open cell or closed cell: what changes in the numbers?
The R per inch. The DOE spray foam guide gives about 3.6 per inch for open-cell, half-pound foam and 6 per inch for typical closed-cell, 2-pound foam, so the same R-value takes 1.67 times the thickness, and the board feet, in open cell. Each foam has its own quote field here. Replace the R per inch with the figure on the data sheet of the product you are quoted.
Is there an app version of this spray foam calculator?
The page runs in a phone browser with nothing to install and no account. The estimate prints, and the CSV export keeps every surface with its thickness, board feet and quote, which is the line-by-line record a second bid has to be compared against.
How would I price a 30x40 shop?
A 30 by 40 shell has 140 feet of perimeter, so the walls are 140 times the eave height, and the roof is 1,200 square feet plus whatever its slope adds. Enter walls and roof separately: 2 inches of closed cell on the walls and an open-cell roof built to the zone’s attic level produce very different board feet. If the shop is a work space and the foam stays exposed, keep the thermal barrier line.
What this estimate does not price
- Board feet are geometry: square feet times inches over the whole surface, studs, joists and rafters included. Overspray, trimming waste, travel and minimum charges are not added; ask whether your quote includes them.
- No pitch factor. Enter a roofline by its length along the slope, or as a known area.
- ENERGY STAR levels are retrofit recommendations, the code ceiling figures are DOE’s summary of the 2021 IECC, and what applies to your work is set by your jurisdiction’s adopted code.
- The barrier rules were read in Seattle’s adoption of the 2021 IRC. Your building department decides which barrier applies, and whether a tested foam needs one.
- R per inch defaults are typical figures from a 2009 DOE guide; aged values vary by product.
- Spending figures are self-reported, cover every insulation type, include do-it-yourself jobs that usually exclude labor, and are top-coded on the public file.
- No vapor, moisture or air-sealing design: whether a roof deck can take open-cell foam in your climate is a design question this page does not answer.