Attic Insulation in Ontario (2026): Cost, R-60, Blown Cellulose vs Fibreglass, Air Sealing, Depth Chart, Removal, Cathedral Ceilings, Hatch and Pot Lights

Insulation & Air SealingAttic

Attic Insulation: Measured From the Ruler, Priced by the R-Point, and Air Sealed Before a Single Bag Goes In

The attic is the cheapest R-value in the house and the easiest job to do badly. Central Ontario rates, October 2026, installed.

Most attics I look at have two problems and one of them is not the insulation. The fluff is thin, yes; but under it the top plates, the plumbing stack, the pot lights and the hatch are letting the house breathe straight into the roof, which is why there is frost on the nails and ice at the eave. These pages do the attic in the right order: find out what is there, seal the floor, then blow the R-points on top, with the baffles, the hatch and the pot light covers priced so nobody finds them on the invoice.

Price my attic The cost guide Air sealing first

The numbers

$0.065per sq ft per R-point added, blown
$1.00per sq ft, air sealing the attic floor
17 in.of cellulose for R-60
$1,250top rebate tier, if the attic starts at R-12 or less

The guides

Attic insulation cost in Ontario

The cost page: blown cellulose and fibreglass per square foot, three attics worked through, and what moves the price.

The attic R-value rule

R-60 and where it comes from, what the inspector checks, and what an older house actually needs.

Blown cellulose vs fibreglass

The two products that go in by hose: R per inch, settling, fire, dust, cost, and which one for your attic.

Attic air sealing guide

The leak list, the materials, the order, the cost, and what to photograph before the insulation covers it.

Insulation depth to R-value chart

Inches to R for every product, how to read the ruler, and what settling does to the number.

Attic insulation removal cost

When the old stuff has to come out, when it does not, the vacuum truck, contamination, and the price.

Attic insulation inspection checklist

Before, during and after: depth markers, coverage over the plates, baffles, hatch, pot lights.

Cathedral ceiling insulation

Vented or unvented, foam on the sheathing or dense pack, the R-31 rule, and the ice dams it stops.

The hatch and the pot lights

The two leaks everyone forgets, IC vs non-IC lights, covers, the hatch box, and what each costs.

Attic ventilation

Already on the site: the 1-in-300 rule, soffit and ridge, and why venting does not fix a leaky ceiling.

Four rules for an attic

  1. Seal the floor before the insulation goes on. After is too late; nobody finds the top plates under 17 in. of cellulose. The list.
  2. Keep the eaves open. Baffles in every rafter bay or the new insulation fills the soffit and the attic stops breathing. Ventilation.
  3. Leave the vermiculite alone. Test it; if it is asbestos, a licensed crew removes it and then the attic gets insulated. Vermiculite.
  4. Get the depth in writing. Depth markers in the attic, bag count on the invoice, R-value on the contract. The checklist.

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