Attic Insulation in Ontario: R-Values, Costs and When It Pays

The attic is usually the cheapest place in an Ontario home to cut heat loss. Warm air rises, the attic floor is often easy to reach, and many houses built before the 1990s still have the thin layer of insulation they were built with. Topping it up is rarely glamorous, but it is one of the few upgrades that improves both winter heating bills and summer comfort upstairs.

This guide explains how much insulation you likely need, what the options cost, what to fix first, and when an attic upgrade is not the best use of your money.

How much insulation does an Ontario attic need?

Insulation is rated by R-value: resistance to heat flow. Higher is better, but each additional R adds less benefit than the one before it. Going from R-12 to R-30 makes a large difference; going from R-50 to R-70 makes a small one.

Situation	Typical existing level	Suggested target
Pre-1970 home, never upgraded	R-8 to R-15 (often 75–100 mm of old batts or loose fill)	R-50 to R-60
1970s–1980s home	R-12 to R-20	R-50 to R-60
1990s–2000s home	R-28 to R-40	R-50 to R-60 if access is easy; often lower priority
New home under the current Ontario Building Code	Around R-60 (depends on the SB-12 compliance package)	Usually no upgrade needed

As a rough rule, loose-fill fibreglass or cellulose gives about R-3 to R-3.7 per inch (25 mm). Reaching R-60 typically means 400–500 mm (16–20 inches) of total depth. You can check what you have by measuring the depth in a few spots with a ruler, taking care not to step between joists.

Colder parts of the province benefit more. A home in Sudbury or Thunder Bay (roughly 5,000–5,700 heating degree days) loses considerably more heat through a poorly insulated attic than the same home in Toronto (roughly 3,500–3,600). Ottawa sits in between at around 4,500.

Air seal first, then insulate

Insulation slows heat moving through materials. It does very little to stop air moving through gaps. In most Ontario attics, warm, moist indoor air escapes through openings in the ceiling below: around pot lights, plumbing stacks, wiring holes, the attic hatch, and the top of interior partition walls.

That leakage wastes heat and, in winter, carries moisture into a cold attic where it can condense on the roof sheathing. Frost on nails, mould on the underside of the roof, and ice dams at the eaves are common signs.

Before any insulation goes in, a good contractor will:

Seal the top plates of walls and gaps around penetrations with foam or caulk.
Box and seal around recessed lights (or confirm they are IC-rated and airtight).
Weatherstrip and insulate the attic hatch.
Make sure bathroom and kitchen fans vent to the outdoors, not into the attic.
Install baffles at the eaves so insulation does not block soffit ventilation.

Insulation options compared

Option	Typical use	Pros	Cons
Blown-in cellulose	Topping up open attics	Low cost per R, fills gaps well, recycled content	Settles somewhat over time; must be kept dry
Blown-in fibreglass	Topping up open attics	Low cost, does not absorb water, does not settle much	Slightly lower R per inch than cellulose; can be less effective at very low temperatures if installed loosely
Fibreglass or mineral wool batts	DIY or small areas	Easy to buy; mineral wool is fire resistant	Hard to fit without gaps around joists and wiring
Spray foam (closed cell)	Cathedral ceilings, tight spaces, rim areas	Air seals and insulates in one step	Expensive; installer skill matters; not usually needed for open attics

For a standard open attic with an accessible hatch, blown-in loose fill is almost always the best value.

What does it cost, and what will it save?

Costs vary by region, access, and how much prep is needed. These are typical 2026 ranges, not quotes:

Blowing in insulation to reach about R-60 in an average 100–140 m² (1,100–1,500 sq ft) attic: roughly $2,000–$4,500.
Air sealing done at the same time: often $500–$1,500 extra.
Removing old contaminated or damaged insulation: can add $1,500–$3,000 or more.

Savings depend on your starting point. As an illustration, a 1970s Toronto home heated by gas, using about 2,400 m³ per year, might cut heating use by roughly 5–15% by going from R-12 to R-60 with proper air sealing. At an example cost of 45¢/m³, that is roughly $50–$160 a year on gas. In an electrically heated home, or one with oil or propane heat, the dollar savings are usually several times higher.

That means attic insulation alone often has a long payback in a gas-heated home that already has R-30 or more. It is much more attractive when the existing level is low, when the home uses electric resistance or oil heat, or when the upstairs is uncomfortable in summer.

To estimate your own numbers, try our insulation savings calculator.

Rebates for attic insulation

According to Save on Energy, the Home Renovation Savings Program (HRS) has offered up to $1,250 for standalone attic insulation through a route that does not require a home energy assessment. Through the assessment stream, insulation incentives have been higher (up to $7,700 for non-gas-heated homes), but that route requires pre- and post-retrofit assessments and at least two upgrades.

Income-eligible households may qualify for free insulation through the Energy Affordability Program or the Enbridge Home Winterproofing Program. See our Home Renovation Savings Program guide and rebates directory for details.

Note: Program rules, amounts and deadlines change. Confirm everything on saveonenergy.ca or enbridgegas.com before you sign a contract.

Checklist before you hire

Measure your current insulation depth and note the type.
Check for vermiculite, mould, wet insulation or signs of pests.
Ask for the target R-value and installed depth in writing.
Confirm air sealing is included and itemized.
Confirm baffles, hatch insulation and fan venting are addressed.
Ask whether the contractor will provide the documentation a rebate requires.
Get at least two quotes.

When attic insulation is not your priority

If you already have R-40 or more, few signs of air leakage and a comfortable home, your money may be better spent elsewhere: air sealing the basement rim joist, upgrading an old heating system, or addressing a cold, uninsulated basement. A home energy assessment can rank these for your specific house. See our home energy assessment guide.

Frequently asked questions

Can I add new insulation on top of old insulation?

Usually yes, as long as the old insulation is dry, free of mould and pests, and is not vermiculite. Loose fill can be blown directly over old batts or loose fill.

Is it a DIY job?

Rolling out batts is possible for a handy homeowner, and some stores lend blowing machines. The difficult part is the air sealing and working safely around wiring and eaves. Many homeowners find a professional job is worth the cost, particularly if they want a rebate that requires documentation.

Will more insulation cause moisture problems?

Not if air leaks are sealed and eave ventilation is kept open. Problems usually come from warm, moist air leaking into the attic, not from the insulation itself.

How long does attic insulation last?

Properly installed and kept dry, it generally lasts for the life of the house. Cellulose settles slightly in the first few years, which reputable installers account for by blowing in extra depth.