Wall insulation cost

Start with what is missing. No real wall job has been priced for this site, so no installed wall price appears on it. The cost model here builds a price out of parts you can check: a trade wage from the Bureau of Labor Statistics, a bag price, and a coverage chart. Those parts describe one job. A crew walks into an attic and blows fiberglass across the floor. A wall is drilled, packed and patched. Using the attic number on a wall would be wrong at both ends.

The material is easier to price on a wall than in an attic, for one odd reason. In an attic you choose a depth. In a wall you do not. The cavity is as deep as the stud is wide, and nothing you buy changes that. So the amount of material falls out of two things you can measure. The area of the wall, and the depth of the cavity.

One more figure sets it. How hard the material is packed. The Building America Solution Center, which the Department of Energy runs at Pacific Northwest National Laboratory, publishes what to aim at. Dense-packed cellulose is 3.5 to 4.5 pounds per cubic foot. Blown fiberglass is 1.8 to 2.6. After that it is weight, volume and a shelf price.

Method. Cavity depth in inches, divided by 12, gives the cubic feet behind one square foot of wall. Times the density gives the pounds. Divided by the bag weight and times the bag price gives the dollars. Both prices were read at The Home Depot on 2026-08-11: $15.97 for a 25 pound bag of cellulose, and $67.58 for a 27.5 pound bag of blown fiberglass.

Read the first row, because most walls are shallower than the other two. A 2x6 cavity holds $1.02 to $1.32 of cellulose per square foot of wall. A 40 foot wall, 8 feet tall, is 320 square feet, so the material for it is roughly $328 to $422. That is the whole material bill. Everything else in the price is people, machines, holes and repair.

Blown fiberglass costs about twice as much here, and the reason is not quality. It is sold by the pound, and a wall wants a lot of pounds. The Department of Energy puts dense-packed fiberglass at 4.2 R per inch and dense-packed cellulose at 3.2 to 3.5, so the glass buys back some of that in performance. Cellulose against fiberglass compares the two in full.

The open wall, where batts and kits are options

A closed wall takes blown material only. An open wall takes anything, and the pricing works differently: a batt covers area at a fixed thickness, so the thickness has to match the cavity or the batt is the wrong product. These are the batts this site holds prices for.

Two of those batts are attic products and the table says so. Only the stone wool one matches a cavity depth this site carries. The batts sold for a normal wall are thinner, and no price for them is held here, so none is printed. The foam rows show why a kit is not a wall plan: filled solid, it costs five to ten times the blown materials above it, and the maker calls its own yield "theoretical", which is a way of saying you will get less.

What these figures are not. Five limits, and they all matter more than the numbers.

• Material only. No labor, no delivery, no drilling, no plugs, no patching, no paint.
• Shelf prices. One store, one day, read on 2026-08-11. A contractor pays less than this, and how much less has not been measured here.
• The fiberglass bag is an attic product. This site holds a price for one blown glass product, Owens Corning AttiCat blown-in fiberglass, 27.5 lb bag, and it is sold for attics. The wool a crew blows into a wall comes in a different bag.
• The R-values are worked out, not measured. Depth times a published R per inch, rounded down at both ends.
• A cavity is not a wall. Studs, sheathing, siding and drywall all count, and the studs are a path for heat around the insulation. A whole-wall figure takes a hot box test, ASTM C1363, and this site has run none.

Same material, same square foot, more money. These are the reasons, and they are reasoning rather than arithmetic. No wall multiplier is published here, because none has been measured.

There is a number worth holding on to here, even though it is an attic number. In this site's attic model, labor works out at $0.47 to $0.95 a square foot, against $1.71 of material at R-49. Two of the inputs behind that are estimates rather than measurements, and it is a floor you can walk on. Every line in the table above pushes a wall's labor over it. How far over is what a quote tells you and this page cannot.

This is the part that turns two similar bids into two different jobs. Filling a wall means making holes in the outside of a house, or in the inside of a room. Those holes are somebody's problem afterwards, and the quote decides whose.

Repair is not one job either. Vinyl siding unclips and goes back, and old vinyl cracks in cold weather. Wood siding is pried, renailed and painted. A discontinued profile cannot be matched at all. Brick is drilled through mortar joints and repointed. Stucco is patched, and a patch on a weathered wall usually shows. Drywall is patched, sanded, primed and painted. Paint runs wall to wall, not patch to patch, so an inside job often means the whole room.

No price for any of that is published here. Siding, masonry and paint are other trades, and no figure for them has been read from a source this site can point at. That is a real gap, and filling it with a guess would be worse than leaving it open.

What you can do is force it into the light. Ask for the fill and the making good as separate lines. Ask who owns a siding piece that breaks on the way off. Ask whether paint is in or out, and whether that means the patch or the room. Three answers, and most of the gap between two bids is inside them.

One thing is not going to help with the bill. There is no federal tax credit for insulation placed in service after December 31, 2025, because Section 25C was terminated for it. Pages all over the internet still say otherwise. What the internet gets wrong carries the citation. If a bid leans on that credit, the bid is out of date.

A single number with no detail behind it cannot be compared with anything. Five items make two quotes the same job, and every one of them is a fair thing to ask for in writing.

Two more are worth having. The wall area the quote is priced on, in square feet, and whether windows and doors were taken out of it. And whether a thermal camera pass happens before the holes are closed, which is the only cheap moment to fix a bay that never took material.

Wiring can change the whole job, not just a line of it. Cloth-covered wire on ceramic knobs is knob-and-tube. Insulation does not go over it. That is an electrician's call first, under the National Electrical Code, published as NFPA 70. States and cities adopt that code on their own timetables. Knob-and-tube wiring under insulation covers what that costs you in time and order of work.

1. Get the area, then divide. Ask what wall area the price is built on, in square feet, and whether windows and doors came out of it. Divide the total by that area. Now you have dollars per square foot of wall, which is the only unit two bids share.
2. Split fill from repair. Ask for two lines. The fill is drilling, blowing and plugging. The repair is siding, patching and paint. Compare fill against fill first. A bid that will not split has told you something.
3. Pin the material and the density. Get the material name, the pounds per cubic foot, and the cavity depth. Take the material cost off the table above. What is left is what you are paying for the crew, and it should look sane next to the labor figures further up this page.
4. Count the holes and name the painter. Holes per bay, who plugs them, who patches, who paints, and whether a camera pass is included. Any missing answer is a difference between two bids that you have not seen yet.

The recommendation. Compare bids on dollars per square foot of wall for the fill alone, at a stated density and cavity depth, with the repair priced beside it and not inside it. Do that and the cheapest number is usually still the cheapest job. Skip it and the low bid is often one hole per bay, no camera, plugs left proud and paint on your side of the line. If only one bidder will answer all four, that answer is worth paying a little more for, because the failure in this work is invisible on the day it happens.

We do not sell insulation and we do not install it, which is why this section can tell you to keep your money. In most houses the attic comes first, and it is not close.

Read the last row twice. The attic figure is a whole installed job, crew and all. The wall figure is material sitting on a shelf, before anybody drills a hole. The wall still costs more per point of R-value. The material alone for that cavity is 47 to 50 percent of what the entire attic job costs per square foot. Insulation cost per square foot shows the attic side in full.

The reason is the box. A wall cavity stops at the depth of the stud. An attic takes another layer whenever you want one, which is why ENERGY STAR recommends R-60 for a bare attic in climate zones 4 through 8 and R-49 in zones 2 and 3. No wall in the table further up gets near either.

So four walls are not worth quoting yet, and one is.

• Any wall, while the attic is thin. Measure the attic with the depth checker first. If it comes back more than about R-10 short of the level for your zone, that is where the money goes. That threshold is this site's own estimate, not a measured figure.
• A wall that already has something in it. The first inches do most of the work, and a tube cannot get past an old batt. Opening walls to insulate them runs that case to the end.
• One cold room, before you know why. It is usually a duct, a knee wall or a floor over a garage. See knee walls and the room over the garage.
• A wall you would open just for this. Drywall, wiring and paint cost more than the insulation does.
• The one worth quoting. Empty cavities, attic already done, and siding due for replacement anyway. Then the holes cost nothing to repair, because they disappear under the new siding.

There is also a cheaper job available in nearly every house. Sealing the ceiling costs little in materials, and on most houses it buys more comfort than the next layer of anything. Whatever a code sets is a separate question from all of this. 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.

• Wall insulation: which walls are worth doing
• Blown-in wall insulation, hole by hole
• Is it worth opening walls to insulate them?
• Insulation cost per square foot
• What attic insulation costs
• Cellulose against fiberglass
• Do it yourself, or hire