Attic R-value
What’s the R-valueof your attic?
A ruler pushed into the insulation is all it takes. You see what it’s worth, what’s missing to hit the target, and what you’d save on heating.
3Your region and your attic
For example, 6 in. of fiberglass is about R-18, or 35% of the target. At R-51, this attic would save about $180 a year in heating.
Estimate for an electrically heated home, at Hydro-Québec’s Rate D (11.142¢/kWh), based on your region’s average weather (Environment Canada). It only counts heat lost through the ceiling. Over 20 years, about $3,600 at today’s rate. How we estimate it
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How to measure your insulationA ruler, a flashlight, five minutes.
No need to be handy. The attic hatch is often in a closet or in a hallway ceiling.
- 01
Open the hatch
Bring a flashlight and a ruler or a tape measure. No need to go in, you can measure at arm’s length.
- 02
Push the ruler down to the ceiling
Push it straight into the insulation until it touches the drywall, without packing it down. Read the height at the top.
- 03
Take the average
Insulation is often settled or uneven. Take three or four measurements in different spots and keep the average.
If you go in, step only on the joists. Between them, the ceiling won’t hold you. And if you see golden-beige granules, it may be vermiculite. Don’t touch it.
R-value per inch, by insulationThe numbers behind the tool.
R-value adds up with thickness. Six inches of an insulation at R-3 per inch is R-18. Here are the values the calculation uses, and the thickness needed to reach R-51.
| Insulation | R-value per inch | To reach R-51 |
|---|---|---|
| New blown fiberglass | 2.8 | 18 in. |
| New blown cellulose | 3.2 | 16 in. |
| Spray foam | 6.0 | 8.5 in. |
| Existing fiberglass | ≈ 3.0 | we blow fiberglass on top |
| Existing cellulose, settled | ≈ 3.7 | we blow fiberglass on top |
| Sawdust | ≈ 2.2 | we blow fiberglass on top |
| Vermiculite | ≈ 2.1 | remove it first |
Average values for dry insulation in good condition. We always confirm on site, for free.
R-value questionsThe short answers.
How do I calculate the R-value of my insulation?
Multiply the thickness in inches by the R-value per inch of your insulation. For example, 6 inches of fiberglass at about R-3 per inch gives about R-18. The tool above does the math for you.
How much can I save by insulating my attic?
It depends on the existing insulation, the area and your region. For an average 950 sq. ft. attic with 6 inches of fiberglass near Montreal, going to R-51 saves about $180 a year in heating for an electrically heated home. Pick your region and attic size in the tool above for your own estimate.
What R-value should an attic in Quebec have?
The target in Quebec is R-50. In the attic, our installations aim for R-51, about 18 inches of blown fiberglass when starting from scratch.
How many inches should I add on top of my current insulation?
It depends on what’s already there. Enter your insulation and its depth in the tool above, and it shows what’s missing to reach R-51. On insulation in good condition, we only blow in the difference.
How do I know which insulation I have?
Fiberglass looks like fluffy white, pink or yellow cotton. Cellulose is grey, like shredded newspaper. Vermiculite comes as light, shiny, golden-beige granules. Sawdust is found mostly in older homes. When in doubt, choose “I don’t know” and the tool gives you a range.
What if my attic has vermiculite?
Don’t disturb it. Vermiculite installed before 1990 is presumed to contain asbestos until proven otherwise, and we never add insulation on top without an assessment. Removal is done under containment, following CNESST rules. See vermiculite removal
Is there a grant to insulate the attic?
Yes. Hydro-Québec’s LogisVert grant can go up to $1,500, and we handle the application.
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The calculator measures your attic area by satellite and texts you your firm price. An attic at the target means about 30% savings on heating.
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