How Much Attic Insulation Do You Need in Ontario?
R-60 is the level currently recommended for attics in this climate zone. In practice that means roughly 16 to 20 inches of blown insulation, depending on the material. Most GTA homes built before the 2000s measure between R-20 and R-35 — well under half of what is recommended today.
Why R-60, and why it keeps moving
Recommended attic levels have risen steadily for forty years, because the cost of energy rose and the cost of insulation did not. A house that met code in 1985 was never wrong — it is simply built to a standard that has since been superseded twice.
This matters when someone tells you their attic 'was done'. Done in which decade, to which level, and has anyone measured it since? Insulation settles, gets compressed by storage, and gets displaced by anyone working in the attic.
Depth is not the same as performance
An attic at R-60 with unsealed top plates, open pot lights and a bathroom fan venting into the space will still lose heat and can develop moisture problems. Air movement carries far more heat than conduction through a well-insulated layer.
This is why we air seal before adding depth, and why we treat ventilation as part of the same job. Insulation without air sealing is the most common way a well-intentioned upgrade underperforms.
What each level looks like
| Level | Approximate depth | Where you usually find it |
|---|---|---|
| R-20 | 5 – 7 inches | Pre-1980 homes, never upgraded |
| R-31 | 9 – 11 inches | 1980s and 1990s construction |
| R-40 | 12 – 14 inches | 2000s construction, or an older top-up |
| R-60 | 16 – 20 inches | Current recommendation for this climate zone |
Follow-up questions
Can I have too much insulation?
There is a point of diminishing return, and it is above R-60 for this climate. The bigger risk is blocking soffit ventilation while adding depth, which is what baffles prevent.
Does the material change the depth?
Yes. Cellulose and fibreglass reach the same R-value at slightly different thicknesses, which is why we record both depth and material rather than depth alone.
General guidance for homes in the Greater Toronto Area. Every building is different — treat this as background, not as a specification for your project.
Want this checked on your own house?
The assessment is free and there is no obligation. You get the findings explained on site and the quote in writing afterwards.
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