Blown-In Insulation Calculator: 2027 Attic & Wall Costs

How to Use the Blown-In Insulation Calculator

Fill it in from the top down. Your answer under Areas to Insulate decides which questions come next.

1. Building Size. The length and width of the house in feet. Attic and wall area are worked out from that footprint.
2. Insulation Type. Cellulose or fiberglass.
3. Areas to Insulate. Attic only (the default), walls plus attic, or walls only.
4. Wall questions (floors, who patches the holes, stud size) appear for wall jobs. A 2×6 wall holds more material than a 2×4, so it costs more to fill.
5. Attic R-Value appears when the attic is part of the job: code minimum, maximum, or your own number.

Prices follow the location in the calculator’s heading. Wrong place? Click “change” and enter your ZIP.

Picking an attic R-value

The code-minimum setting is R-30 in warmer states and R-38 in colder ones. Maximum means R-49 in warm climates and R-60 in cold ones. A custom entry is an R-value, not a depth: figure roughly R-3.3 to R-3.7 per inch of cellulose, depending on the brand, and about R-2.9 per inch of fiberglass.

In a cold state, go past code. You’re already paying for the truck, the hose and the crew, so extra depth mostly costs extra bags.

Who patches the holes?

Filling a closed wall means drilling a 2-3″ hole into every stud bay, usually through the drywall inside. Old plaster and lath cracks when drilled, so crews often work from outside instead, lifting a course of vinyl siding or boring through wood clapboards.

Pick “Contractor” and the insulation crew plugs and finishes the holes, which the calculator prices at roughly 55-75 cents per square foot of wall. Pick “Homeowner” if you or a handyman will do it. Repainting those rooms anyway? That’s easy money saved.

What Blown-In Insulation Costs

For a typical 2,000 sq ft house, blowing cellulose into the exterior walls (R-13) and topping the attic up to R-38 costs about $5,560 to $7,570, hole patching included. Fiberglass adds roughly $1,630 to $2,210. An attic-only cellulose job usually lands between $1,850 and $3,470.

Installed prices per square foot (walls before patching):

• 2×4 walls: cellulose $1.21-$1.67, fiberglass $1.27-$1.73, closed-cell foam $2.70-$3.72
• Attic at R-60: cellulose (about 16″ deep) $2.36-$3.23, fiberglass (about 21″) $3.57-$4.90, closed-cell foam (about 8.5″) $6.64-$9.01

Foam rarely makes sense on an open attic floor. There’s room for a thick, cheap layer of loose fill, and that’s where blown-in pays off best.

Air sealing and insulating an under-insulated house typically cuts heating and cooling bills by around 15%, more in a drafty older one. To see what that’s worth to you, run your fuel use through our home heating cost calculator. Replacing the furnace or AC soon? Insulate first, then size the new system with our heat pump calculator, because a tighter house usually needs a smaller unit.

Finished Walls, Open Attic, or Gut Job?

Which insulation fits depends mostly on what shape the house is in right now.

Finished walls, and you live there

Blown-in wins. Anything else means tearing off drywall, which turns an insulation job into a renovation. Dense-packed cellulose brings a 2×4 wall to about R-13, which is respectable for an older house.

Attic only

Loose fill is usually the cheapest R-value on an open attic floor. Batts work too, and foam suits cramped knee walls. Loose fill only stays put on a flat surface, though, so a vaulted ceiling or the underside of the roof deck needs batts or foam. Compare them all in our attic insulation cost calculator.

Gutted to the studs, or new construction

With the framing open, closed-cell foam earns its price: close to double the R per inch of loose fill, plus an air and vapor seal in the same pass. Batts are the budget choice.

For scale, taking a 1,000 sq ft attic to R-38 costs roughly $1,500-$2,080 in blown cellulose and about $4,210-$5,720 in closed-cell foam. Unless you need foam’s air seal, that difference buys a lot. Full foam pricing is in our spray foam insulation calculator.

Cellulose or Fiberglass?

Check the deal-breakers first. Choose fiberglass if any of these apply:

• The walls or attic have had leaks, condensation or high humidity. Fiberglass can dry out and keep working. Wet cellulose holds water and can grow mold.
• Someone in the house has asthma or another breathing problem. Installing cellulose kicks up a lot of fine dust.
• Your installer won’t put “dense-pack” for the walls in writing (see below).

If none of those apply, cellulose is probably the better buy. It packs more R into the same cavity: about R-13 in a 2×4 wall versus roughly R-10 for fiberglass. The bags also cost around 25% less, though per inch that’s only a couple of cents a square foot.

Settling. Loosely blown cellulose sinks more than 10% over time. In attics, installers blow a little deeper than the target to allow for it. In an 8-foot wall, settling can leave an empty gap near 10 inches tall under the top plate. Dense-packing prevents it, but it’s slower and the contractor isn’t paid extra for it, so some crews skip it. Write “dense-pack” into the contract.

Fire. Cellulose sold for homes is treated with borate and ammonium sulfate, and treated fill puts itself out once the flame is gone. Fiberglass won’t burn, but enough heat melts it away from the studs and leaves the wood behind it exposed.

Rebates and Tax Credits for Insulation

Some state programs have covered as much as three-quarters of an insulation bill. The federal energy tax credit for insulation has expired, so ask your tax preparer about state credits instead.

Read the rules before you book. Most programs cover blown cellulose only, on a standard attic-and-wall job, done by their approved contractors at prices the program sets. Plenty of older, under-insulated homes still qualify.

Call your utility and your state energy office, then get free quotes from local installers so you have something to compare.

Blown-In Insulation FAQ

How deep should blown-in insulation be in the attic?

For R-38, about 10-12 inches of cellulose or 13 inches of fiberglass. For R-60, about 16-18 inches of cellulose or 21 of fiberglass.

Can I blow insulation over old batts?

Usually. If the old batts are dry, with no mold or rodent damage, loose fill can go right on top, and both layers count toward your R-value.

How long does an attic blow-in take?

Most attics take a day, often just a few hours of actual blowing. Walls take longer, since every bay has to be drilled, filled and plugged.