Insulation Cost Per Square Foot

This is the number most people are looking for: what a contractor charges per square foot, materials and labor together, for a finished job. The table below is the 2026 national average for each common job type.

Read it as a starting point rather than a quote. The same crew will price the same attic differently depending on access, headroom, how many recessed lights need dams built around them, and whether anything has to come out first.

Blown-in is the cheapest way to get a deep attic R-value, which is why it dominates attic work. Blown fiberglass and blown cellulose land within about fifteen cents of each other per square foot installed at R-49, and the choice between them is usually about the material rather than the price.

Cellulose is denser, settles more, and does better at slowing air movement through the layer. Fiberglass is lighter, does not absorb water the way cellulose does, and is easier to top up later. Both need the same air sealing underneath them to perform as rated — insulation slows conduction, it does not stop a draught.

DIY changes the arithmetic more here than anywhere else, because the machine is usually free with a big enough bag order. Material only at R-49 runs roughly $0.90–$1.60 a square foot at retail bag prices; the constraint is that blowing an attic properly is a two-person job, one feeding the hopper and one on the hose.

Fiberglass comes two ways and they price differently. Batts and rolls in an open wall run about $1.75 per square foot installed at R-15; blown fiberglass in an attic runs about $1.85 at R-49, for far more R-value, because blowing is quicker than cutting and fitting.

That is the thing people find counter-intuitive: the deeper attic job costs about the same per square foot as the thinner wall job. Walls cost more per unit of R-value because every bay is cut to fit, split around wiring, and stapled.

Mineral wool sits above fiberglass on both price and performance — R-4.0 per inch against R-3.2, better fire resistance and noticeably better sound damping, for about 50% more material cost at the same R-value.

If you are doing the work yourself, labor comes out of the number entirely and the comparison changes shape. Below is what the material alone costs per square foot, normalised to R-30 so the materials are actually comparable rather than being quoted at whatever thickness each is usually sold in.

Normalising matters. Polyiso looks expensive per inch and comes in cheaper than XPS per unit of R-value, because at R-6.0 per inch you need fewer inches of it. Quoting board prices per inch without saying what R-value that inch buys is how rigid foam gets a reputation it does not deserve.

Per-square-foot pricing is easy to misread, because the square footage that matters is the attic floor, not the house. A 2,000 sq ft two-storey house has roughly a 1,000 sq ft attic, and quoting the job against the wrong number doubles the estimate.

The table below runs the three common attic jobs across the sizes people actually have.

Spray foam is sold by the board foot — one square foot at one inch thick — not by the square foot, which is why it looks cheap next to batts until you multiply by depth. Open-cell at the 3.5 inches that fills a 2x4 wall works out around $1.95 per square foot; closed-cell at 2 inches is around $3.60.

Closed-cell buys more than R-value: at around 2 inches it also works as a vapour retarder and adds racking strength, which is why it shows up in crawl spaces, rim joists and coastal construction where the others do not.

Two-part DIY kits exist and are genuinely useful for rim joists and small sealed areas. They are not a cheaper route to a whole attic — by the time you have bought enough kits, a contractor with a rig is usually less money.

Removal is the big one. Pulling out contaminated or water-damaged insulation before re-insulating adds roughly $1.55 per square foot, which can be a third of the whole job and is the single most common reason a quote comes in far above an online estimate.

Access is next. An attic you can stand up in prices differently from one you crawl through on your stomach, and a hatch in a cupboard prices differently from a pull-down stair. Crews price the awkwardness, not just the area.

Then there is scope creep that is usually worth agreeing to: air sealing the ceiling plane before insulating, building dams around recessed lights and the flue, and adding baffles so the new depth does not block the soffit vents. None of that is padding — insulation blown over unsealed penetrations underperforms its rating for the life of the house.

Insulation is one of the few home upgrades where the payback is arithmetic rather than opinion. Heat loss through a surface is its area times the temperature difference divided by its R-value, so going from R-19 to R-49 cuts loss through that surface by about 60% — and the first inches do most of the work.

That is the part worth understanding before spending: the jump from R-11 to R-19 saves far more than the jump from R-49 to R-60, because you are dividing by a bigger number each time. Topping up a badly under-insulated attic is excellent value; chasing the last few R-points rarely is.

Federal and utility incentives change the maths again where they apply, and they are worth checking before you book rather than after.

Cut the bill with 2026 insulation rebates and tax credits.