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Basement Insulation Cost in Ontario (2026): Four Wall Assemblies Priced on a 36×28 House, Per Square Foot, What Moves the Number, and the Rebate Reality
Insulation & Air Sealing
Basement Insulation Cost: Three Ways to Get a Concrete Wall to R-20, One Way to Have It Already, and What Each One Costs on a Real House
A basement wall in Ontario has to end up at R-20 effective, full height, from under the subfloor to the slab, if you are finishing it. There are three common ways to get a poured or block wall there and they land within $1.20 a square foot of each other: $9.60 for foam board and a stud wall, $8.75 for spray foam and a stud wall, $8.40 for a 2×6 wall with batts and poly. The fourth way is an ICF basement, which needs nothing added because the foam is the form. On a 36×28 house with 984 sq ft of wall, the first three run $8,970 to $10,150 before HST with the rim joists done. Here is where every dollar goes.
The numbers
$9.60Assembly A, foam board and 2×4 wall, per sq ft
$8.75Assembly B, 3 in. closed cell and 2×4 wall, per sq ft
$8.40Assembly C, 2×6 wall with batts and poly, per sq ft
$5.50rim joist, 2 in. closed cell, per lf
| Line item | Per sq ft of wall | R added | Notes |
|---|---|---|---|
| Rigid foam against the concrete, 1.5 in., taped | $2.75 | R-7.5 | XPS or Type II EPS, joints taped, edges foamed. Too thin on its own. |
| Rigid foam, 2 in. | $3.50 | R-10 | The usual layer under Assembly A. Low enough permeance to be the vapour retarder. |
| Rigid foam, 3 in. | $4.75 | R-15 | Two layers staggered. Eats floor space; hard to fasten through. |
| Closed cell spray foam on the concrete, 2 in. | $2.50 to $4.00, default $3.00 | R-12 | Foam at $1.00 to $1.50 a board foot plus masking; a small basement costs more per foot because it hits the minimum charge. See the rim and masking lines. |
| Closed cell, 3 in. | $4.25 | R-18 | The Assembly B layer. Seals every crack and the top of the wall in one pass. |
| 2×4 stud wall at 24 in. o.c., foam sill, gap off the concrete | $4.50 | Framed and blocked. Not the drywall. | |
| 2×6 stud wall | $5.50 | Only needed when the batt is doing all the work (Assembly C). | |
| R-14 fibreglass batt in the 2×4 wall | $1.10 | R-14 nominal | Adds about R-11 effective behind the foam. |
| R-22 mineral wool batt in the 2×6 wall | $2.40 | R-22 nominal | Does not hold water the way fibreglass does; still a batt against concrete. |
| 6 mil poly, acoustical sealant, tape | $0.50 | Only where the assembly has no foam doing the vapour job. Never over foam. | |
| Rim joist, 2 in. closed cell, per linear foot | $5.50 per lf | R-12 | $4 to $7. Includes the top of the wall and the joist ends. The rim joist page. |
These are the lines the spray foam cost calculator uses for the foam, with the masking, backing and minimum charge added the way a foam contractor adds them. Drywall over any of it is a separate line.
The four assemblies, side by side
| Assembly | Layers, concrete outward to the drywall | Per sq ft | Effective R | What it is good and bad at |
|---|---|---|---|---|
| A, what most contractors do | 2 in. XPS taped + 2×4 wall + R-14 batt + poly | $3.50 + $4.50 + $1.10 + $0.50 = $9.60 | about R-21 | Dependable, every trade knows it. The poly is the argument; see below. |
| B, foam and frame | 3 in. closed cell on the concrete + 2×4 wall, no batt, no poly | $4.25 + $4.50 = $8.75 | R-19 to R-21 | Best air seal of the four, no vapour-barrier debate, needs the crew and the minimum charge. |
| C, batts alone | 2×6 wall + R-22 mineral wool + poly, gap off the wall | $5.50 + $2.40 + $0.50 = $8.40 | R-20 nominal | Cheapest on paper. A batt against cold concrete needs the moisture barrier and the gap done exactly right or it grows mould. |
| D, ICF basement | Nothing added. The form is 2.5 in. of EPS each face of the concrete. | $0 of insulation | R-22 and up | No studs, no poly, no batts; drywall screws to the webs. The wall itself is priced on the ICF pages, not here. |
The code number is R-20 effective, full height, and all four get there. Assembly A lands about R-21 because the foam is continuous and the batt sits behind it; Assembly B is R-18 of foam plus the drywall and dead air; Assembly C is R-22 nominal in the batt and about R-20 with the studs counted, which is why it is a 2×6 wall. Which one to specify is its own page; this one is about the money.
The 36×28 house worked through
Bungalow, 36 by 28 ft outside, 8 ft poured walls, five basement windows totalling 40 sq ft, unfinished and dry. Perimeter 128 lf times 8 ft is 1,024 sq ft of wall; less the windows, 984 sq ft. The rim joist runs the same 128 lf.
Assembly A: 984 sq ft at $9.60 is $9,446. Rim joists, 128 lf at $5.50, $704. Subtotal $10,150. HST $1,320. Total $11,470.
Assembly B: 984 at $8.75 is $8,610, plus the rim at $704, $9,314 before HST, $10,525 with. The whole foam job, 3 in. on the walls and 2 in. at the rim, is one visit and about 3,170 board feet, which is well past any minimum charge. Ask whether the $300 of masking is in the $4.25; it is the first thing a low quote leaves out.
Assembly C: 984 at $8.40 is $8,266, plus the rim at $704, $8,970 before HST, $10,136 with. It saves $1,180 against Assembly A, and the saving is real only if the wall is bone dry, the gap is held and the poly is sealed like a boat. I do not build it; it is here because it is what the cheapest quote will be.
Assembly D: $0, because an ICF basement does not get a second insulation job. The rim and the under-slab foam are still real; the walls are not. ICF against the poured wall runs the whole comparison.
What moves the price
- Wall height. A 9 ft wall on the same house is 1,152 less 40, 1,112 sq ft, and Assembly A becomes $10,675. The code number is full height, so nobody stops the foam at the frost line to save money.
- A small job and spray foam. Two men, a truck and a rig do not go out for 400 sq ft of wall. Under about 600 sq ft, expect a minimum of $900 to $1,500 whatever the per-foot arithmetic says. Bundle the rim, the mechanical room wall and the cantilever into one visit.
- Backing. Open joist bays at a cantilever, a knee wall, the top of a block wall: the foam needs something to shoot against, $2.00 a square foot of cardboard or OSB, and it is never in the per-foot rate.
- The wall is wet. No assembly here is a fix for a wet wall. Efflorescence, a damp line at the floor, a crack that weeps in April: those get fixed first, and the fixing can cost more than the insulation. The tests before anyone insulates.
- Walkouts and block. A walkout has one wall that is really an above-grade frame wall at R-22; price it separately. Hollow block leaks air through every core and the top course, so Assembly B or a foamed top course is the honest answer there.
The rebate reality
There is no standalone basement rebate. The Home Renovation Savings program pays an attic rebate without an energy assessment; basement, wall and exposed-floor insulation only count on the assessment path, with an EnerGuide evaluation before and after at $500 to $800. On that path the bundled insulation rebate is set by the evaluation, up to $1,250 to $7,700 for walls, basement, exposed floor and air sealing together, with pre-approval before the work starts and a full cycle of three to six months. Funding is reported as running through November 30, 2026 with no published end date, which means it can close earlier.
So the rule: never let a quote subtract a rebate. If you qualify, up to the program amount comes back afterward, and only after the second evaluation. The program page has the mechanics and the energy audit page has the evaluation; check the program site before you sign anything.
Questions people ask
How much does it cost to insulate a basement in Ontario?
$8.40 to $9.60 a square foot of wall for a code-compliant full-height assembly with a stud wall, plus $5.50 a linear foot for the rim joists. A 36×28 bungalow with 984 sq ft of wall is $8,970 to $10,150 before HST. Drywall, electrical and flooring are extra. An ICF basement needs none of it.
What R-value does a basement wall need in Ontario?
R-20 effective, full height, for a finished basement under the common SB-12 package, or R-12 plus R-10 continuous in some packages. The house’s own SB-12 form says which.
Is spray foam worth the money in a basement?
On this house Assembly B comes in about $840 under Assembly A before HST, at $1.25 a board foot, and it buys the best air seal and ends the poly argument. Where it costs real money is a small job that trips the minimum charge, or a block wall that needs backing.
Can I get a rebate for basement insulation?
Only on the assessment path of Home Renovation Savings, with an EnerGuide evaluation before and after, bundled with the other insulation work, and never as a standalone. Nobody can promise the amount; check the program site before you sign.
Does the price include drywall?
No. These rates are the insulation and the stud wall. Drywall is on its own page, and exposed foam in a living space needs the 1/2 in. drywall as a thermal barrier before anyone moves in, so it is not optional on Assembly B.
Price your walls and the rim together
The spray foam cost calculator takes the wall area, the height, the thickness and the rim and shows the board feet, the masking and whether you are under the minimum. If you have quotes that say “R-20 basement package” and nothing else, the $99 review finds out which of the four assemblies that is.
Sources and further reading
- Ontario’s Building Code, Supplementary Standard SB-12: the energy-efficiency packages that set the R-values for attics, walls, basements and slabs in a new or renovated Ontario house.
- Home Renovation Savings: the Enbridge and IESO program page: streams, eligibility, participating contractors and current amounts; check it before you sign anything.
- Keeping the Heat In: Natural Resources Canada: the plain-language Canadian guide to air sealing, insulation materials, basements, walls and ventilation.
