Most Canadian attics should be insulated to roughly R-50 to R-60, and many older homes have far less, often R-10 to R-20 or patchy coverage. Topping up an accessible attic with blown-in insulation is one of the most cost-effective efficiency upgrades available, typically costing roughly $1,500 to $4,000 for an average home when done by a pro (approximate). Done right, it starts with air sealing, keeps attic ventilation working and avoids a few hazards that are common in older Canadian houses.
Key takeaways
- Target roughly R-50 to R-60 in most of Canada; check your provincial building code and local guidance for your climate zone.
- Blown-in cellulose or fibreglass is the most common choice for topping up an existing attic.
- Air seal the attic floor before adding insulation, or you'll lose much of the benefit.
- Professional blown-in jobs are often fast and affordable; DIY is possible but messy.
- Watch for vermiculite (possible asbestos), knob-and-tube wiring and blocked soffit vents before you start.
What R-value means
R-value measures resistance to heat flow; the higher the number, the better the insulation. In Canada you'll also see RSI, the metric equivalent (R-value ÷ 5.68 ≈ RSI). So R-50 is about RSI 8.8, and R-60 is about RSI 10.6.
R-value adds up with depth. The material you choose determines how thick the layer needs to be:
| Material | Approx. R-value per inch | Depth for ~R-50 | Notes |
|---|---|---|---|
| Blown-in cellulose | R-3.2 to R-3.8 | ~14–16 in | Recycled paper, treated for fire resistance; dense, good at reducing air movement |
| Blown-in fibreglass | R-2.2 to R-2.9 | ~18–22 in | Lightweight, won't absorb moisture; needs more depth |
| Fibreglass or mineral wool batts | R-3.0 to R-4.0 | ~13–16 in | DIY-friendly in open attics; gaps reduce performance |
| Closed-cell spray foam | R-6 to R-7 | ~7–8 in | Also air seals; much more expensive; used in tricky areas |
Values are approximate and vary by product. Check the bag or manufacturer's data for coverage charts.
How much does your attic have now?
Grab a tape measure and a flashlight. Measure the depth of insulation in several spots, away from the hatch. Then estimate:
- Under 6 inches: probably R-20 or less. A top-up will likely pay off well.
- 6 to 12 inches: roughly R-20 to R-40. Worth topping up in most of Canada.
- 12+ inches, evenly spread: you may already be close to modern levels.
Look for bare spots, compressed areas and places where insulation was disturbed by electricians or cable installers. An EnerGuide evaluation will measure this for you and model the savings.
Step one: air seal first
Insulation slows heat conduction, but fibrous insulation doesn't stop air. Warm, moist air rising through gaps in your ceiling can carry heat into the attic and cause frost, mould and ice dams. Before you add insulation:
- Seal around plumbing stacks, wiring holes, duct penetrations and the tops of interior walls.
- Seal and insulate the attic hatch, and add weatherstripping.
- Box in older recessed lights that aren't rated for insulation contact, or replace them with airtight, IC-rated fixtures.
- Seal gaps around chimneys with sheet metal and high-temperature sealant, keeping required clearances.
Our air sealing guide covers this in more detail.
Keep the attic ventilated
Most Canadian attics are designed to be cold and ventilated, with air entering at soffit vents and leaving through roof or ridge vents. When adding insulation:
- Install baffles (vent chutes) at the eaves so insulation doesn't block soffit airflow.
- Keep insulation away from roof vents.
- Don't vent bathroom fans into the attic; duct them outdoors.
Good ventilation plus good air sealing helps prevent ice dams and moisture damage.
Costs: DIY vs. professional
Approximate Canadian ranges:
| Approach | Typical cost for ~1,000 sq ft attic | Pros | Cons |
|---|---|---|---|
| DIY blown-in (machine often lent free with bag purchase at some retailers) | $700–$1,800 in materials | Lowest cost | Dusty, two-person job, hard to get even depth |
| DIY batts | $900–$2,000 in materials | No machine needed | Harder in low-slope attics; gaps reduce performance |
| Professional blown-in top-up | $1,500–$4,000 | Fast, even coverage, often includes baffles | Higher cost |
| Professional air sealing + insulation | $2,500–$6,000 | Best results | Highest upfront cost |
| Old insulation removal (if needed) | $1,500–$5,000+ extra | Fixes contaminated or damaged attics | Adds cost and time |
Costs depend on attic size, access, existing conditions and region. Some provincial and utility programs have offered incentives for insulation, sometimes requiring an energy evaluation first; use our rebate finder to see current options.
When DIY makes sense
- Your attic is easy to access with good headroom.
- There's no vermiculite or old wiring concerns.
- You're comfortable working on joists with a mask, goggles and long sleeves.
When to hire a pro
- Low-slope roofs or tight access.
- Signs of moisture, mould or ice dams.
- You want air sealing, baffles and insulation done together with consistent quality.
Hazards to check first
- Vermiculite: Pebbly, grey-brown or gold insulation in older homes may contain asbestos. Don't touch it; have it tested and, if necessary, removed by a qualified contractor.
- Knob-and-tube wiring: Have an electrician assess it before covering it with insulation.
- Pests and mould: Address these before adding new material.
- Bathroom or kitchen fans venting into the attic: Redirect them outside.
How much will you save?
Savings depend on how little insulation you have to start, your climate and how you heat. Going from very low levels to R-50 or more generally produces the biggest improvement, while adding to an already well-insulated attic yields diminishing returns. Homes in colder regions, such as the Prairies and the North, see larger savings. Lower heat loss also means a heat pump can be sized smaller and run more efficiently.
Frequently asked questions
Can I put new insulation on top of old insulation?
Usually yes, as long as the existing insulation is dry, free of mould and pests, and isn't vermiculite. Blown-in material can go directly over old batts or loose fill.
Is cellulose or fibreglass better for a Canadian attic?
Both work well. Cellulose is denser and better at limiting air movement within the insulation layer, while fibreglass is lighter and won't absorb moisture; installer experience matters more than the choice of material.
Will more attic insulation stop ice dams?
It helps, but ice dams are mostly caused by warm air leaking into the attic. Air sealing, adequate insulation and good attic ventilation work together to prevent them.
The bottom line
For most Canadian homes, bringing the attic up to roughly R-50 to R-60 is a high-value, relatively low-cost upgrade. Air seal first, protect your soffit ventilation, check for hazards, then add insulation evenly. It's a natural early step in our whole-home upgrade sequence.
Sundamentals is an independent, non-profit education platform. Program details and prices change often — check current programs for your address in our rebate finder.