Spray Foam Insulation Cost Calculator (2027 Prices)

How to Use the Spray Foam Calculator

Grab a tape measure. Ten minutes of measuring gets you an estimate you can hold a bid up against.

1. Footprint and stories. Measure the length and width of the house from outside and enter the number of stories. Each story counts as 9 feet of wall: an 8-foot ceiling plus the floor framing above it. A raised ranch gets 1.4 times the wall area, a factor that has tracked closely with real raised-ranch jobs we’ve priced. Taller ceilings mean more wall, so expect a little more.
2. Foam type. Open or closed cell. Haven’t decided? Run it both ways and look at the gap.
3. Target. Code Minimum sprays only the thickness your inspector needs to sign off. Maximum R-Value fills every bay flush with the framing. A 2×6 wall packed with 5.5″ of closed cell comes out near R-38.
4. Wall studs. Lumber is smaller than its name: a 2×4 bay is 3.5″ deep, a 2×6 bay 5.5″. A full 2×4 tops out near R-24 in closed cell and around R-12 in open cell.
5. Attic approach. Spray the attic floor between the ceiling joists, or seal the whole attic by foaming the rafters and gable walls. Then enter the depth of whichever members get the foam.
6. Roof pitch. Counts only when you seal the roof deck, because that’s when the triangular gable ends get sprayed. The tool assumes a gabled roof, since hip roofs are less common. Foaming just the joists? Skip it.
7. Windows and doors. Each window takes out roughly 9 sq. ft. (sized off a common 2.5′ x 3.5′ unit), and each standard 36″ entry door takes out 21 sq. ft.
8. Region. Matches labor and material rates to your market. Not sure which one fits? Leave it on National Average.

One run worth doing: price Walls Only in open cell and Attic Only in closed cell, add them up, and compare that mix with doing the whole house in one foam.

How Much Does Spray Foam Cost?

Installers price it two ways. Know both before the first bid lands.

Per square foot of house. Spread over the floor area, plan on roughly $2.88 to $5.17 per sq. ft. for open cell and $5.07 to $8.44 per sq. ft. for closed cell. That covers the exterior walls and the attic at code-level R-values. Two-story houses land toward the low end, since there’s less attic per square foot of floor.

Per board foot. This is how crews actually bid. A board foot is one square foot of foam, one inch thick. Closed cell runs about $0.79 to $1.07 a board foot and open cell $0.34 to $0.52, a bit more in high-cost markets like the West Coast.

The board-foot rate is your lie detector. Multiply the area being sprayed by the inches of foam on the bid, then by the rate. If the bid comes in well above that, ask what else got folded in. No bids yet? Ask local spray foam installers to quote your house, and have each one list the inches of foam planned for the walls and the attic.

Closed cell prices jumped during the supply crunch a few years back and never fully came down. Open cell barely moved. A loyal repeat customer might get a nickel off, but no honest crew discounts closed cell much below the low end of that range.

The biggest price swings come from foam type (closed cell costs about double per inch), framing depth, sealing the roof deck instead of just the attic floor, and filling every cavity to the brim instead of stopping at code minimum.

Only doing the attic? The attic insulation cost calculator is the better tool. It lines spray foam up against blown-in fiberglass or cellulose and batts, so you can see whether foam even makes sense up there.

Open Cell vs. Closed Cell Spray Foam

Closed cell costs roughly twice as much per inch. Here’s what the extra money buys, and when the cheaper foam is fine.

Closed cell: dense, tight and waterproof

At about 2 lb. per cubic foot, closed cell delivers around R-6.75 to R-7 per inch. Nothing else commonly used in houses beats that. It’s also its own vapor barrier, so moisture can’t drift through the wall in either direction, and drifting moisture is what slowly rots sheathing and framing. Water doesn’t soak in, so a small roof leak won’t turn it into a wet sponge. And it shuts down air leaks almost completely, which fiberglass and cellulose can’t do.

The downsides are price and expansion. It doesn’t swell as much, so it struggles to fill eaves and tight corners. Good crews hit those pockets with a little open cell and spray closed cell everywhere else.

Open cell: cheaper, softer, thirstier

Open cell is light (about 0.5 lb. per cubic foot), rated near R-3.5 per inch, and costs about half as much. In mild climates where an R-13 2×4 wall passes code, that’s real money saved on install day, and it’s easy to spray and trim flush.

The weak spot is moisture. At around 15 perms, open cell lets vapor through, and that vapor can get stuck in the foam. Damp foam means mold and rotted wood. In an attic you may need an added vapor retarder and sometimes drywall over the foam, and that eats most of the savings.

So is closed cell worth it? Usually. You get about double the R-value plus a built-in vapor barrier for about twice the price per inch, so cost per R comes out close to even. Lower energy bills often pay it back in 3 to 7 years, depending on your climate and fuel prices. Check that against your own rates with the home heating cost calculator.

Code R-Values Often Pick Your Foam for You

Requirements change from state to state and sometimes town to town, so confirm with your building department. These targets are common:

• Retrofits (existing homes): R-15 walls, R-38 attic, R-30 crawl space.
• New construction: R-21 walls, R-49 attic.

Open cell tops out around R-12 in a 2×4 wall, so it can’t reach R-15. Closed cell gets there with only about 2.1 inches. Overhead, R-38 in closed cell means filling a 2×6 cavity, and R-49 takes a full 2×8. Getting R-38 out of open cell would take nearly 11 inches of foam, deeper than most rafters. In a lot of places, that takes open cell off the table for attics and 2×4 walls.

Should open cell go in the attic?

Our advice: closed cell for attics and roof decks, in any climate. Besides the R-value problem, open cell isn’t a vapor barrier. Warm, humid indoor air pushes through it, cools, and leaves the foam and roof sheathing damp. Field studies in cold-climate states have turned up exactly that in open-cell attics, and damp foam is how mold starts.

In climate zone 5 and colder, open cell in an attic generally needs an added vapor retarder. That’s why so many northern builders skip it. Once you count the extra layers, closed cell ends up cheaper.

In warm and mild climates, builders, building scientists and foam makers still argue about it, and some insist open cell works fine there. Maybe so, but the price gap is small next to the energy savings, and closed cell ends the moisture debate.

How Much Can Spray Foam Save on Heating Bills?

A bare 2×4 wall scores about R-4 from the siding, sheathing, air gap and drywall combined. Fill the 3.5″ cavity with closed cell, figuring a conservative R-6 per inch, and you add about R-21, for roughly R-25 total.

Heat loss is Q = U × A × ΔT. U is 1 divided by the R-value, A is the area in square feet and ΔT is the gap between indoor and outdoor temperature. Take 2,000 sq. ft. of exterior wall, a 70°F house and a 5°F night, so ΔT is 65:

• R-4 wall: 2,000 ÷ 4 × 65 = 32,500 BTU lost per hour
• R-25 wall: 2,000 ÷ 25 × 65 = 5,200 BTU lost per hour

That’s 27,300 fewer BTUs escaping every hour, a bit more than six times less heat loss. With natural gas at about $2 per therm (100,000 BTU), that one hour saves you around 55 cents.

To scale it up to a full winter, use heating degree days (HDD), which add up how far each day’s average temperature falls below 65°F. Chicago averages about 5,649 HDD. Multiply by 24 to get degree-hours:

• R-4 wall: 2,000 ÷ 4 × 5,649 × 24 ≈ 67.8 million BTU per season
• R-25 wall: 2,000 ÷ 25 × 5,649 × 24 ≈ 10.8 million BTU per season

The gap is about 56.9 million BTU, or roughly 569 therms. At $2 a therm, that’s about $1,100 a year, from the walls alone.

The bonus: smaller heating and cooling equipment

A tighter house needs less equipment, and a 55,000 BTU furnace is cheaper to buy and install than an 80,000 BTU model. The same goes for heat pumps and AC. The swing can be huge: a well-insulated 2,000 sq. ft. Illinois home might get by with around 28,000 BTU of heat, while the same house with poor insulation could need more than 160,000.

A whole house is messier than one wall, with the attic, windows, basement, ducts and air leaks all in play. Run the furnace size calculator before and after the upgrade to see the difference (it works for boilers and heat pumps too), and the HVAC load calculator for cooling.