Insulation and Air Sealing in Ontario: Attic, Spray Foam, Basement, Walls, Costs, Rebates and How to Hire the Trades, From a Builder

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Insulation and Air Sealing in Ontario: What It Costs, Why More R-Value Is Not the Answer to a Cold House, and What the Quote Has to Say Before You Sign It

Written by a builder who has insulated 300-plus houses, most of them ICF, where the wall is the insulation and the only argument left is the attic. Prices are Ontario rates checked October 2026, installed.

People buy insulation the way they buy a sweater: thicker must be warmer. Then they put a thicker sweater on a house with the windows open, which is what an attic top-up without air sealing is. Insulation slows heat; it does not stop air, and air carries the heat and the moisture that ends up as frost on the sheathing and water on the basement poly. These pages cover the attic from the ruler up, spray foam by the board foot with the masking and the minimum charge that never make the brochure, the basement assemblies that work against concrete and the one that grows mould, the effective R-value of a wall with the studs counted, the rebates with their conditions, and how to hire and check the people who do the work.

Price my attic Read the cost guide Review my quotes, $99

The numbers

Central Ontario, installed, before HST. Checked October 2026.

$2.60per sq ft, attic top-up R-20 to R-60
$1.25per board foot, closed-cell spray foam ($1.00 to $1.50)
$9.60per sq ft, basement wall, foam plus studs plus batt
R-17what a 2×6 R-22 batt wall really is

A 1,200 sq ft attic from R-20 to R-60 with the air sealing, hatch, pot lights and baffles is about $5,400 with HST. A 36×28 basement insulated full height with foam against the concrete and a stud wall in front is about $11,500. The whole insulation package on a new 2,000 sq ft frame house is about $23,500; the same house in ICF has about $7,300 of insulation work left to do because the walls and basement came insulated.

Start here

Attic insulation and ventilation

Cost, the R-60 rule, cellulose vs fibreglass, air sealing, the depth chart, removal, cathedral ceilings, the hatch and the pot lights.

Spray foam and insulation materials

Foam by the board foot, foam vs mineral wool, fibreglass vs mineral wool, rigid boards, cellulose, foam problems, the thermal barrier.

Basements, foundations and crawlspaces

The assemblies priced, what goes against concrete, rim joists, crawlspaces, the wet-poly problem, slabs, ICF vs poured.

Walls, airtightness and new homes

Air sealing cost, the blower door, effective R, flash and batt, ICF and extra insulation, the air barrier checklist, ventilation.

Costs, rebates, quotes and contractors

The master price table, the new-house package, the rebates and their catch, insulation or heat pump first, comparing quotes, hiring, inspection, the contract, vermiculite, knob-and-tube, older houses.

The calculators

Three of them, on one set of rates. Use the one that matches the job.

Attic insulation cost calculator

Existing depth to existing R, the top-up to R-50 or R-60 priced by the R-point, air sealing, pot lights, hatch, baffles, removal, HST, and the rebate tier check. Start here for an attic.

Spray foam cost calculator

Surface by surface at the thickness you need, closed or open cell by the board foot, rim joists by the foot, masking, backing, the thermal barrier and the minimum charge.

Wall assembly comparison calculator

The same house seven ways, 2×6 batts to ICF: installed cost, effective R with the studs counted, heat through the walls in your fuel, and the 20-year total.

Heat loss calculator

Already on the site: the whole house, which is what the insulation changes and what the furnace or heat pump is sized from.

Six things I tell every customer about insulation

  1. Air seal first. Then insulate. In that order, every time, or the insulation is a filter for the air going through it. The leak list.
  2. Measure what is there before anyone sells you more. A ruler in the attic tells you the R-value you have and the rebate tier you are in. The chart.
  3. Foam is sold by the board foot, so buy it that way. Thickness on every line, R-value beside it. Foam costs.
  4. Nothing fibrous goes against concrete. Foam on the wall, then the studs, then the batt if you want one. A batt on bare concrete is a sponge with a vapour barrier over it. Concrete walls.
  5. The bag says R-22; the wall says R-17. The studs are in the wall whether the brochure counts them or not. ICF has no studs. Effective R.
  6. Fix the water before the insulation. Wet batts, a leaking roof, a bath fan into the attic, a damp basement wall: insulation over any of them is money on top of a mistake. The checks.

Have quotes or plans in hand? Let a builder read them first

For $99, I put your attic, spray foam, basement or air-sealing quotes on one grid, check the area and the existing R-value against your house, name the product and the depth each one actually promised, price the air sealing, baffles, hatch and removal that was left out, check the rebate claim, and tell you which one to sign. For a new build or an addition, $249 turns your plans into a whole-house insulation takeoff, attic, walls, basement, rim and slab, with the SB-12 number each assembly needs and a scope three contractors can price the same way.

Insulation quote review, $99 Insulation takeoff, $249 Check the quotes yourself first

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