Wall Insulation Cost Calculator
Wall Insulation costs $2,925 to $4,425 for a typical 1,200 sq ft job in 2026, against a national benchmark of $3,575. Labor runs 26 crew hours at $39.00 an hour. Enter a ZIP code to apply that area's measured wages for this work and its regional price level.
What makes up the price
Cost by size
National averages, before any local adjustment. Computed from the same model as the calculator above, so the two always agree.
| Wall area | Sq ft of wall | Typical | Range |
|---|---|---|---|
| 650 sq ft | 650 | $2,100 | $1,725 to $2,600 |
| 950 sq ft | 950 | $2,900 | $2,375 to $3,600 |
| 1,200 sq ft | 1,200 | $3,575 | $2,925 to $4,425 |
| 1,600 sq ft | 1,600 | $4,650 | $3,825 to $5,775 |
| 2,050 sq ft | 2,050 | $5,875 | $4,800 to $7,275 |
The R-value is not a choice
Everywhere else in the house, insulation decisions are about depth. In a wall there is no depth decision: a 2x4 stud cavity is 3.5 inches and anything that fills it gives R-13 to R-15. A 2x6 wall takes R-19 to R-21. That is the whole range.
So the question is not what R-value to buy. It is how the material gets into a closed cavity, and what it costs to make the holes disappear afterwards:
| 1,200 sq ft of wall | Per sq ft | |
|---|---|---|
| Through siding | $3,575 | $2.98 |
| From inside, drilling drywall | $4,125 | $3.44 |
| Through stucco or brick | $4,825 | $4.02 |
| Through stucco, two stories | $5,550 | $4.62 |
The access card moves the price by more than 50%. The material choice moves it by a third. That is the reverse of every other insulation job, and it is why the useful questions on this page are all about the holes.
Walls come after the attic, and it is not close
| Cost | What it buys | |
|---|---|---|
| Attic, blown cellulose | $1.88 / sq ft | R-49 |
| Wall, dense-pack | $2.98 / sq ft | R-13 |
Six tenths more money for a quarter of the R-value, over a smaller area, with patching afterwards. In a house with a thin or bare attic, spending wall money on the attic instead buys three or four times the result.
That is not an argument against insulating walls. Empty wall cavities in a cold climate are worth filling, and the air-sealing effect of dense-pack is worth more than its R-value suggests. It is an argument about order: attic, then rim joist, then walls.
The one piece of advice that saves real money
If the siding is coming off anyway, insulate then.
| 1,200 sq ft | |
|---|---|
| Batts in an open wall | $2,675 |
| Dense-pack through siding | $3,575 |
| Dense-pack through stucco | $4,825 |
The gap between the first and the last is $2,150, and all of it is drilling and patching. A re-side, a gut renovation, a room being taken back to the studs — any of those is the cheapest wall insulation will ever be, and the window closes when the new siding goes on.
So: if a siding quote and an insulation quote are both on the table, get them to talk to each other. And if you are re-siding next year, do not insulate this year.
Knob-and-tube wiring stops the job
If the house was wired before about 1940 and still has any knob-and-tube — single conductors running through porcelain tubes and knobs, with no ground — this has to be resolved before anything is blown into a wall.
Knob-and-tube is designed to shed heat into open air. Most jurisdictions, following NEC 394.12, prohibit filling a cavity that contains concealed knob-and-tube wiring, because insulation around those conductors traps heat in a cloth-insulated wire that has already had ninety years to become brittle.
What this means in practice:
- An insulation contractor who knows the trade will look in the attic and pull an outlet cover before quoting. One who does not look is one to avoid.
- If live knob-and-tube is present, the answer is to have it replaced before insulating, not to insulate around it.
- Many insurers take a view on knob-and-tube independently of this, so it is worth knowing either way.
An older house may also have balloon framing, where the wall cavities run uninterrupted from the basement to the attic. That is a strong reason to dense-pack — those cavities are a chimney for warm air — and a reason the crew will want to see the house before giving a number.
Are your walls already insulated?
Worth establishing before paying anybody to find out. Three ways, cheapest first:
- Pull an outlet cover. Turn off the circuit, take off a plate on an exterior wall, and look into the gap at the side of the box with a flashlight. You can usually see fiberglass, cellulose, or nothing.
- Look on a cold morning. With frost on the roof or a chill in the air, an uninsulated wall feels noticeably colder to the hand than an insulated one, and in many houses you can see the studs as stripes in the frost on exterior walls or in condensation.
- Have a thermal scan done. An infrared camera shows empty cavities, settled fill and missed bays unambiguously. Energy auditors charge $200 to $600 for a scan with a blower-door test, and if you are considering $3,500 of wall insulation it is money well spent — it also tells you whether the attic or the walls are the actual problem.
A common finding is partially insulated walls: batts installed in the 1970s that have slumped, leaving the top foot of every cavity empty. Dense-pack fills around and above them, which is one of the better uses of this work.
Dense-pack or injection foam
| Dense-pack cellulose | Injection foam | |
|---|---|---|
| 1,200 sq ft | $3,575 | $4,800 |
| R-value in a 2x4 | about R-13 | about R-15 |
| How it fills | Packed to 3.5 lb/cu ft | Pours in wet, cures in place |
| Air sealing | Good | Slightly better |
| Track record | Decades, extensively studied | Good, with one caveat |
Dense-pack is the standard retrofit and the right default. The density is the point: at 3.5 pounds a cubic foot — four times what the same cellulose is blown at in an attic — it does not settle in a vertical cavity and it resists air movement well enough to count as partial air sealing.
Injection foam is a pourable resin foam, not the spray foam used on a roof deck. It goes in wet through a small hole and cures slowly in place, which lets it find gaps dense-pack cannot. It costs about a third more for two more points of R.
The caveat worth knowing: the urea-formaldehyde foam of the 1970s shrank, off-gassed and was withdrawn, and it is the reason injection foam still carries a reputation. Modern products are different chemistry. If you are considering it, ask what the product is, how long that formulation has been in use, and to see a house done five years ago.
Getting it checked
Dense-pack is one of the few trades where the work is invisible the moment it is finished, so ask for two things:
- Every bay filled to refusal, and the voids probed. A cavity interrupted by fire blocking needs two holes, one above and one below, and a bay with a window header above it needs its own. Missed bays are the normal failure.
- A thermal scan afterwards, or at least on a sample of the wall. On a cold day an infrared camera shows a missed cavity instantly. Some contractors offer this as standard; most will do it if asked beforehand.
Also ask what happens to the holes: who patches, who paints, and whether the siding that comes off will go back on with new clips or the old ones.
What you are paying for
1,200 square feet of wall dense-packed through siding, at $3,575:
| Labor, about 26 hours | around $1,420 |
| Dense-pack cellulose, 1,200 sq ft | $660 |
| Plugs, patching and touch-up | $420 |
| The crew and the machine | $150 |
| Overhead and margin | the balance |
Labor is 40% of this job against 28% on an attic, and the materials are a fifth of it. That is the shape of wall insulation: you are mostly paying for a hole in every stud bay, a nozzle fed into each one, a probe to check it filled, and a plug — about eighty times for a typical house.
Questions worth asking
- Is there knob-and-tube wiring in this house?
- Are the cavities empty, partly filled, or already done?
- Where are the holes going — siding, inside, or through the stucco?
- Who patches and who paints?
- How do you handle fire blocking and bays above windows?
- Will you probe every bay, and can we do a thermal scan afterwards?
- Dense-pack or injection foam, and why that one here?
- If injection foam: what product, and can I see one done five years ago?
- Is the siding coming off anyway at any point?
- Which utility rebates apply, and do you file them?
Common questions
How much does wall insulation cost?
About $3,575 to dense-pack 1,200 square feet of existing wall through the siding, which is $2.98 a square foot. From inside, drilling and patching drywall, it is $4,125; through stucco or brick, $4,825; and through stucco on a two-story house, $5,550. Injection foam instead of cellulose takes the baseline to $4,800. If the wall is already open, batts are $2,675.
What R-value can you get in an existing wall?
R-13 to R-15 in a 2x4 wall and R-19 to R-21 in a 2x6, and that is the whole range — the cavity is 3.5 inches deep and anything that fills it lands in that band. So unlike an attic, there is no depth decision to make and no upgrade to buy. The money goes on how the material gets into a closed cavity and what it costs to make the holes disappear.
Should I insulate my walls or my attic first?
The attic, and it is not close. Blown cellulose in an attic is $1.88 a square foot for R-49; wall dense-pack is $2.98 a square foot for R-13. That is more money for a quarter of the R-value over a smaller area, with patching afterwards. Walls are worth doing once the attic and the rim joist are done, or when the siding is coming off anyway — not as a first move in a house with a thin attic.
What is dense-pack insulation?
Cellulose blown into a closed wall cavity at about 3.5 pounds a cubic foot — four times the density the same material is blown at in an attic. The density is the point: at that packing it does not settle in a vertical space and it resists air movement well enough to act as partial air sealing, which is worth more in an old house than its R-13 suggests. It goes in through a 2 to 3 inch hole drilled in every stud bay, which is then plugged and patched.
Can you insulate walls without removing the drywall?
Yes — that is what dense-pack and injection foam are for. A hole is drilled in each stud bay, the material goes in under pressure or pours in wet, and the hole is plugged. The holes can come from outside, by taking off a course of siding and drilling the sheathing, or from inside through the drywall. Outside is usually cheaper because the siding goes back with nothing to see, where inside means drywall patching and paint that has to match a whole wall.
Is it cheaper to insulate walls from inside or outside?
Outside, through siding, is the cheap case at $2.98 a square foot: a course of vinyl or lapped wood siding comes off, every bay is drilled through the sheathing, and the siding goes back invisibly. Inside is about 15% more because the drilling is quicker and the finishing is not — patching and repainting a whole wall to match. Stucco and brick are the dear case at about 35% more, since each hole is core-drilled and patched, and on weathered or textured finishes the patches often stay visible.
Can you insulate walls with knob-and-tube wiring?
Generally no, and this needs settling before anybody quotes. Knob-and-tube sheds heat into open air by design, and most jurisdictions, following NEC 394.12, prohibit filling a cavity that contains concealed knob-and-tube. Insulation around ninety-year-old cloth-insulated conductors traps that heat. The answer is to have the wiring replaced first, not insulated around it — and an insulation contractor who does not look in the attic or pull an outlet cover before quoting a pre-1940 house is one to avoid.
How do I know if my walls are already insulated?
Easiest first: turn off the circuit, take an outlet cover off an exterior wall and look into the gap beside the box with a flashlight — you will usually see fiberglass, cellulose or nothing. On a cold morning an uninsulated wall feels markedly colder and you can sometimes see the studs as stripes in frost or condensation. For certainty, an energy auditor's infrared scan with a blower-door test is $200 to $600 and shows empty cavities, settled fill and missed bays unambiguously.
Can dense-pack go over existing wall insulation?
Yes, and partially insulated walls are one of the better uses of it. A common finding in houses insulated in the 1970s is batts that have slumped, leaving the top foot of every cavity empty — dense-pack fills around and above them without anything being removed. What it cannot do is help a cavity that is genuinely full, which is why establishing what is in there comes before getting quotes.
Is injection foam better than dense-pack cellulose?
Marginally, for about a third more money: roughly R-15 against R-13, and slightly better at finding gaps because it goes in wet and cures in place. Dense-pack is the standard retrofit and the right default. The caveat worth knowing about foam is historical — the urea-formaldehyde foam of the 1970s shrank and off-gassed and was withdrawn, which is why the category still carries a reputation. Modern chemistry is different, but ask what the product is and to see a house done five years ago.
How do I know the installer filled every cavity?
Ask beforehand for two things: that every bay is filled to refusal and probed for voids, and a thermal scan afterwards. Missed bays are the normal failure mode, because a cavity interrupted by fire blocking needs two holes and a bay above a window header needs its own. On a cold day an infrared camera shows a missed cavity instantly. Some contractors scan as standard; most will if it is agreed before the work rather than after.
Does wall insulation cause moisture problems?
Dense-pack cellulose has decades of study behind it and is not generally a moisture risk — it can take up and release small amounts of moisture without losing performance, which is one of its advantages in an old wall. The genuine risks are elsewhere: a wall that is already getting wet from failed flashing or a leaking gutter will keep getting wet, and insulation makes the symptom harder to spot. Fix the water first, and in a cold climate ask what the installer expects to happen to vapor in that particular wall assembly.
Where these numbers come from
Nothing here is copied from a contractor directory. Labor is priced from what the trades are actually paid, materials from published producer prices, and both are adjusted to your area using federal cost-of-living data.
- Drywall and insulation contractors, United States: $39.00/hour, August 2026 (BLS CES CES2023831003)
- Dense-pack cellulose, 2x4 cavity: $0.55 per sq ft of wall (price recorded October 2026, not index-adjusted)
- Plugs, patching and touch-up: $0.35 per sq ft of wall (price recorded October 2026, not index-adjusted)