What is the "R-value"?
The R-value measures the thermal resistance of an insulant: the higher the R, the more the insulant slows heat loss. For an attic, it's the number that matters. In Quebec, the target for an attic is R-50 (RSI 8.8).
R-50 or R-60: which to choose?
R-50 is the target in Quebec and the threshold required by the LogisVert grant. At Isolation à Rabais, our attic installations aim for R-51, just above it. Going up to R-60 adds a few more inches of insulation for a gain that becomes small.
| R-value | Blown fiberglass | Blown cellulose | Relevance |
|---|---|---|---|
| R-40 | ~14 in | ~12.5 in | Below target, worth upgrading |
| R-50 | ~17.5 in | ~15.5 in | The target in Quebec |
| R-51 | 18 in | 15.9 in | What we install |
Should you always aim for the highest R possible?
No. Beyond the target, each extra inch of insulation brings smaller and smaller gains while the cost keeps rising. Reaching the target, with a proper installation, gets you most of the comfort without needless extra cost.
Thickness isn't everything
An R-60 attic with poor sealing performs worse than an R-50 with good air sealing. Warm air leaking through the ceiling cancels out part of the insulation. That's why effective insulation combines thickness (R-value) AND caulking, and it's exactly that combination that qualifies you for the LogisVert grant.
How do you find your current R-value?
Our R-value calculator estimates the existing insulation and what's missing to reach R-51. Then our pricing tool gives you the exact cost for your home.
What R-value for your attic?
Estimate your current R-value, then your price to reach the target.
Get my estimate →