Spray foam attic cost

Most spray foam cost pages give you a dollar range per square foot and cite nobody. This one does not, and the reason is worth stating plainly. Pricing an installed foam job needs two halves: a material price and a labor method. This site has read the first and has not measured the second.

So the page gives you the half it can stand behind, and the arithmetic to check a bid with. It stops there rather than dressing a guess up as a range.

For the one material this site does model installed, blown fiberglass, the attic insulation cost hub carries the totals and the method behind them, and blown-in insulation cost prices it per bag and per square foot. The spray foam page covers what the material is and where it belongs.

Three two-component kits, priced by the unit foam is actually sold in. The last column is the one that matters, because a kit price on its own tells you nothing about how far it goes.

Figures: material only, at retail shelf price, read off live product pages at The Home Depot on the dates shown. One retailer on one day. Prices move by store and by ZIP. Nothing here is averaged and nothing is discounted, because a contractor's buying price has not been measured.

Two things fall out of that table. The first is the word the maker chose. One listing calls its yield "theoretical output" and another calls it "theoretical" board feet. That is the manufacturer telling you real yield comes in lower, in its own words, before anyone else says it. Cold cans, a cold surface, a fast trigger and any waste all take from the same number.

The second is that buying a bigger kit barely helps. The two DAP kits sit within a cent of each other per board foot, and the 35 lb one is more than three times the price of the 10.5 lb one. Stepping all the way up to the FROTH-PAK system saves about 20 percent per board foot. Useful, and nothing like the gap between foam and loose fill.

One finding is worth stating because it is an absence. No two-component open-cell kit was found at either retailer on 2026-08-11. The do-it-yourself shelf is closed-cell only. If a page quotes you a homeowner price for open-cell foam, ask what product it came from.

A board foot is one square foot sprayed one inch thick. That is the whole definition, and most homeowners meet it for the first time on a foam quote.

It exists because foam is bought by volume, not by area. A batt or a bag covers floor. Foam fills space, and the same square foot can take two inches or six. So the trade prices the volume and leaves the thickness to the scope.

That gives you one small piece of arithmetic worth memorizing. Board feet divided by the area sprayed equals the average thickness in inches. It runs backward just as well: inches times area equals board feet. Because the unit already carries the inch, board feet per square foot of ceiling is the depth.

Depth is what buys R-value. Closed-cell foam is rated at R-6.0 to R-7.0 an inch, so a target sets the inches, and the inches set the board feet.

Figures: material only. Depths are computed from the R per inch range this site carries for closed-cell foam. Dollars are the DAP Touch 'N Foam Wall and Cavity Low-GWP two-component kit, 35 lb (7565000353) at $2.01 a board foot, read 2026-08-11. The listing calls its yield "theoretical" board feet, which is the manufacturer stating that real yield is lower. The kit is closed-cell; no two-component open-cell kit was found at retail. Larger jobs are contractor equipment, not kits.

The middle two columns hold the same numbers on purpose. That is not a mistake in the table. It is the identity that makes the board foot useful, and seeing it once is usually enough to keep it.

Price the same R-30 off the cheapest kit per board foot instead and material lands at $6.94 to $8.10 a square foot. Still about 7 to 8 times blown fiberglass. Shopping the kit size moves this a little. It does not change the answer.

Foam bids look impossible to compare because each one is a single number for a job nobody has described. Four steps fix that, and they end in a verdict.

1. Get three numbers in writing. The board feet, the thickness in inches, and the area being sprayed in square feet. Also get the product name and whether it is open-cell or closed-cell. Without those, there is nothing to compare.
2. Divide board feet by area. That returns the average thickness. Check it against the thickness you were promised. Say a bid lists 4,000 board feet over 1,342 square feet of roof. That is 3.0 inches, which in closed-cell foam is about R-17 to R-20. If the sales sheet said R-49, the numbers and the promise do not agree.
3. Divide the price by the board feet. That gives dollars per board foot. It is the only unit two foam bids share, and it strips out the fact that one crew measured the roof and the other measured the floor.
4. Compare, and read the answer. Lower total with a higher price per board foot means less foam, not a better deal. Same price per board foot with different totals means the two are pricing different areas or different depths, so go back to step two. A real difference in dollars per board foot should have a named reason: closed-cell against open-cell, the barrier over the foam, removal of the old insulation, or vent work.

The verdict rule. A bid that will not put board feet, thickness and area on paper cannot be judged by you or by anyone else, so ask once and decline if the answer does not arrive. Two bids that both show their numbers can be settled in about a minute with a calculator. That is the whole reason to insist on the unit.

This is the difference that makes a foam bid look inflated when it is not.

Loose fill goes on the attic floor, so it is priced on the floor area. Foam in an attic usually goes on the underside of the roof, which brings the attic inside the heated part of the house. A roof plane is a slope, and a slope covers more surface than the floor beneath it.

That is geometry rather than a survey of houses. The rafter is the long side of a triangle whose base is the run and whose height is the rise, so a steeper roof means more surface over the same floor.

Figures: geometry only, for 1,200 square feet of attic floor. Gable walls and dormers are extra and are not in the table.

The gable walls at each end get sprayed too on most roofline jobs, and they are not in that table. Neither are dormers. So ask for the measured area on the quote rather than working it out from your floor plan.

Run that through the board foot and you get the plainest argument against doing this yourself. A 1,200 square foot attic under a 6 in 12 roof is about 1,342 square feet of deck. Taking that to R-49 in closed-cell foam is roughly 9,391 to 11,001 board feet. That is 15 to 18 of the biggest kit in the table above, the one that holds 630 board feet. Kits are for sealing rim joists and small gaps. A ceiling is contractor equipment.

Three lines turn up with an attic foam job that a loose-fill quote never carries. None of them is priced here, because none has been measured here. All three should appear on the paperwork before you sign it.

The covering over the foam

Foam plastic burns, so it is not left bare inside a building. Section R316.4 of the model International Residential Code asks for a thermal barrier between the foam and the inside of the house, and gypsum board is the usual one. Section R316.5.3 allows something lighter, an ignition barrier, in an attic entered only to service utilities. On sprayed foam that is often a coating rolled or sprayed over the surface.

The IRC is a model code. Which edition applies where you live depends on what your state or city adopted and amended, and your local building department is the only authority on it. What matters for the money is simple: the barrier is real work with a real price, and it belongs on the quote as its own line rather than as a surprise.

Getting the old insulation out

Foam at the roof line moves the boundary of the heated space up to the roof. The insulation lying on the attic floor is then in the wrong place, and it usually comes out. That is a separate job with its own price, its own hours and its own disposal. What removal costs prices the work for loose fill and batts, and the removal guide covers how it runs. If the material is wet, moldy or rodent-fouled, deal with that first either way.

What happens to the vents

Foam sprayed to the roof line takes the soffit and ridge vents out of service. That is not a side effect, it is the design. The attic stops being a vented space and becomes part of the house, which the model IRC treats as its own assembly in Section R806.5, with rules meant to keep the roof sheathing dry.

Two things follow. Baffles and vent work on an insulation quote become irrelevant on a foam quote, so a bid carrying both is worth a question. Soffit and ridge vents covers what is being closed, and the spray foam page covers what replaces it. Half-sealing an attic, foam on part of the roof and open vents elsewhere, is the version that causes trouble.

Price is the last question about foam, not the first. Work down these three in order. The first one that stops you is your answer.

1. Is the insulation going on the attic floor, or on the roof line? If the floor is open and you can reach it, foam is the most expensive way to buy plain depth. The table above is the size of that gap. Verdict: air sealing plus loose fill. Foam against blown-in runs the full comparison.
2. Is there a reason the insulation has to move up to the roof? There are four that hold up. Ducts or an air handler in the attic. A cathedral or low-slope roof with no room for depth. A knee-wall attic that cannot be sealed any other way. Or an attic becoming a finished room. Verdict: if none of those fits, stop here. If one does, keep going.
3. Can the whole job be done, not just the spraying? That means the old floor insulation coming out, the barrier over the foam, and the vents handled as a designed unvented assembly. Verdict: if any of the three has no answer on the quote, it is not ready to price. Get a bid that includes them.

Then ask for all of this in writing, before comparing any two numbers.

• The product name, and whether it is open-cell or closed-cell.
• Board feet, thickness in inches, and target R-value, for every surface being sprayed.
• The sprayed area in square feet, and which surface it is measured on.
• The barrier over the foam: which type, which product, and who inspects it.
• What happens to the insulation already on the attic floor, and who hauls it away.
• Which vents are being closed.
• How long the house has to be empty after the spray, per the product maker.

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We do not sell insulation and we do not install it, which is why this section exists. Most attics that get a foam quote should not buy foam.

The reason is in the numbers above, not in an opinion. R-value does not care what it is made of. A ceiling at R-60 in blown fiberglass slows heat exactly as well as a ceiling at R-60 in foam. At R-30, foam kit material costs about 4 times what blown fiberglass material costs at R-60. Half the R-value, several times the money, for the same job on a floor you can walk on.

What foam adds on an attic floor is the air seal, and you can buy that on its own for a small share of the price. Caulk, canned foam and rigid board around the tops of the walls, the light cans, the pipes, the wire holes and the hatch, all before the loose fill goes over. That is the air sealing job, and on a leaky ceiling it is the better first spend either way.

Two more cases where the answer is to spend nothing this year. If your attic is already within about R-10 of the level for your climate zone, which in zones 4 through 8 means roughly R-50 already down, more depth pays back slowly. That R-10 mark is this site's editorial judgment, labeled an estimate rather than a measurement. And if the attic is dry, clean and simply thin, more of what is already up there is the cheapest right answer. The depth checker turns your measured inches into an R-value range first.

Those levels are ENERGY STAR retrofit guidance for an attic with nothing in it, which ENERGY STAR bases on the model 2021 IECC table. Energy codes cover new building and work done under a permit. They do not usually cover adding insulation to an attic you already have. Which edition applies where you live depends on your state, and often on your city. Your local building department is the only authority on it.

The two foams are priced differently for two separate reasons, and mixing them up is how a cheap-looking bid turns out to be the costly one.

Per inch, open-cell is normally the cheaper material. It is lighter, it uses less chemical to fill the same space, and it goes on faster in thick lifts. This site carries no measured open-cell price, so it publishes none, and no homeowner kit of it was found on the shelf.

Per R-value, the gap narrows, because open-cell needs more inches. R-49 takes about 13.2 to 14.0 inches of open-cell against 7.0 to 8.2 inches of closed-cell. More inches means more board feet, and board feet is what you are billed for.

So the two comparisons can disagree, and the one that matters is per R-value on your surface. Depth also runs into the rafters: a roof deck may not have room for the open-cell version of the same R-value without adding framing. Open-cell against closed-cell covers the rest of the trade, including water, air and vapor, which is where the real decision usually sits.

• Attic insulation cost: the installed total and the method behind it
• Every material priced in the same unit
• Spray foam: where it belongs and where it does not
• Spray foam against blown-in, on the same attic
• Open-cell against closed-cell
• How much R-value your attic needs