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Attic Insulation Calculator

Calculate top-up depth, bag count and material cost for blown cellulose, blown fibreglass, batts. NBC 2020 9.36.2 R-60 climate-zone targets.

Attic Insulation Calculator

Calculate top-up depth, bag count and material cost from attic area, NBC 2020 9.36.2 target R-value and existing insulation.

Top-up depth required
9.1 in
R-value gap to fill: R-32 (5.64 m²K/W)
Equivalent U-value (W/m²K): 0.09 W/m²K
Material count
50 bags
Material cost (CAD estimate)
$850
Reference standard
NBC 2020 9.36.2 / NRCan EnerGuide

What this calculator does

This tool calculates how much attic insulation you need to meet your NBC 2020 9.36.2 R-value target for your climate zone, how many bags or batts to buy, and what the material will cost in 2026 CAD. It works for blown cellulose, blown fibreglass, R-30 fibreglass batts, and Roxul mineral-wool batts.

Enter your attic floor area in square feet, the target R-value (R-60 for most of Canada), and the existing R-value. The calculator returns the R-value gap, top-up depth, bag count, and material-only cost at typical 2026 Home Depot Canada, RONA and Lowe’s Canada pricing.

NBC 2020 9.36.2 climate zones for Canada

The 2020 National Building Code splits Canada into six climate zones based on heating degree days:

ZoneHDDLocationsAttic R-min
4< 3,000Pacific coast lowlands (rare)R-40
53,000 – 3,999Vancouver, Victoria, WindsorR-50
64,000 – 4,999Toronto, Hamilton, Niagara, HalifaxR-60
7A5,000 – 5,999Ottawa, Montreal, Quebec City, Calgary, EdmontonR-60
7B6,000 – 6,999Winnipeg, Saskatoon, Regina, Sault Ste MarieR-60
8≥ 7,000Yellowknife, Whitehorse, Iqaluit, ThompsonR-70

Most major Canadian cities sit in zones 6 and 7A, where the standard NBC 2020 attic target is R-60. BC’s Energy Step Code 4 and 5 push attic R-values to R-70 and R-80 for net-zero-ready and net-zero homes respectively. Quebec’s CCQ Section 11 sets a parallel target system aligned with Rénoclimat audit thresholds.

How the math works

The calculator subtracts existing R-value from target to derive the R-value gap, then divides by R-per-inch of the chosen material to compute installed depth:

depth_inches = R_gap / R_per_inch

Cellulose at R-3.5 per inch with an R-gap of 32: depth = 32 / 3.5 = 9.1 inches loose-laid (about 230 mm).

Bag counts use each manufacturer’s installed-density coverage table. A 19 lb bag of CertainTeed CelloPak covers 30 sq ft at R-30. At R-32 it covers proportionally less (28 sq ft); at R-60 about 15 sq ft. The calculator scales coverage to match the gap-R you’re filling.

Cost data comes from 2026 average prices at Home Depot Canada, RONA, Lowe’s Canada and Réno-Dépôt: C$17 per bag of blown cellulose, C$23 per bag of blown fibreglass, C$48 per bundle of R-30 fibreglass batts, C$58 per bundle of Roxul Comfortbatt R-22.

Existing-insulation depth survey

Slip a yardstick into the loose-fill at three or four points and average. Convert depth to R-value:

  • 6 inches of pre-1990 fibreglass batt, undisturbed: R-19 (label) but real-world R-15 (settled)
  • 8 inches of 2010-era blown cellulose, undisturbed: 8 × 3.5 = R-28
  • 10 inches settled blown fibreglass: 10 × 2.2 = R-22
  • 5 inches of pre-1980 vermiculite (rare in Canada outside QC and AB): STOP — pre-1990 vermiculite from the Libby, Montana Zonolite mine may be asbestos-contaminated. Have a CSA-accredited lab sample-test before disturbing.

For a typical 1990s Toronto two-storey with original R-28 batt insulation, top-up needed to NBC R-60 = 32 R-value, or about 9.1 inches of new blown cellulose cross-laid.

Quebec winter premium

Installer pricing in Quebec carries a 12–18% winter premium November through March, reflecting the productivity cost of working in below-zero attics. Top-ups installed in summer (June–September) cost roughly C$1.05–C$1.55 per sq ft installed; the same job in February runs C$1.30–C$1.95. For DIY, summer is preferable for comfort and dust control. Winter has the advantage of a clear thermographic-imaging baseline for verifying installed coverage — most EnerGuide auditors prefer winter blower-door tests.

NRCan EnerGuide and Canada Greener Homes Loan

The Canada Greener Homes Loan (CGHL) provides interest-free loans up to C$40,000 over 10 years for eligible energy-efficiency upgrades, including attic insulation that achieves at least one full R-step improvement (e.g. R-19 → R-50, or R-28 → R-60). Pre-and-post NRCan EnerGuide audits are mandatory; total audit cost is roughly C$400–C$600 per visit, often rebated by the provincial program (Ontario Save on Energy, BC CleanBC, Quebec Rénoclimat).

The Canada Greener Homes Grant (CGHG, up to C$5,000 in grants plus C$600 audit rebate) closed to new applicants in March 2024, but pre-approved homeowners have until March 2027 to complete and claim. Provincial replacement programs are filling the gap — BC’s renamed CleanBC Better Homes Program, Ontario’s Save on Energy Home Renovation Savings, Quebec’s Rénoclimat, all offer C$1,000–C$2,500 attic-insulation rebates as of April 2026.

Air-sealing and ice-dam mitigation

CRCA’s Roofing Specifications Manual and Natural Resources Canada both flag attic air-sealing as the single highest-leverage retrofit in Canadian climates. The benefits compound:

  1. 15–35% additional energy savings on top of the insulation upgrade alone.
  2. Ice-dam prevention: warm air leaking into the attic melts the snow at the ridge faster than the eaves, refreezes at the colder eave overhang, dams meltwater behind, drives water under shingles. Air-sealing kills the heat-loss source.
  3. Moisture management: fewer warm-air leaks mean less interior humidity reaching cold roof-deck surfaces, reducing the risk of mould on the underside of the deck.

The NRCan retrofit checklist:

  • Caulk or low-expansion-foam interior-wall top plates (the single biggest leak path in most Canadian homes).
  • Foam around plumbing stacks, electrical penetrations, bathroom fan housings.
  • Weatherstrip and insulate the attic hatch — typical loss of 5–8% of total ceiling R-value through an unsealed hatch.
  • Replace pre-2010 pot lights with IC-AT-rated airtight LED retrofits. CSA C22.2 No. 250.0 requires the IC-AT marking for any recessed light in an insulated ceiling.
  • Maintain soffit ventilation: install eaves baffles before blowing loose-fill.

Vapour barrier compliance

NBC 2020 9.25.4 requires a Type 1 or Type 2 vapour retarder on the warm side of the envelope in HDD > 4,000 zones. For attics, this means under the ceiling drywall — typically 6-mil polyethylene sheet stapled to the underside of joists before drywall installation. Most post-1985 Canadian homes have this in place; pre-1985 homes often don’t.

If you don’t have a poly vapour barrier, you can either install a Class III vapour-retarder paint on the ceiling drywall (Sherwin-Williams ProMar Vapour Barrier, ICI Lifemaster Vapour Barrier — both meet ASTM E96 ≤ 1 perm) or install a vapour-permeable smart membrane (Pro Clima Intello, Siga Majrex) above the drywall when re-finishing. Don’t sandwich the existing assembly between two impermeable barriers — that traps moisture.

Frequently asked questions

How much insulation do I need in my attic in Canada?
The 2020 National Building Code (NBC) Section 9.36.2 sets attic minimums by HDD (heating degree days). For HDD ≥ 5,000 (most of Canada including Toronto, Ottawa, Montreal, Calgary, Edmonton and all Atlantic capitals), the attic minimum is R-60. For HDD 4,000–4,999 (Vancouver, Victoria, Windsor) the minimum is R-50. For HDD under 4,000 (almost nowhere in Canada except Pacific coast lowlands) the minimum drops to R-40. Most provinces have adopted NBC 2020; British Columbia uses BCBC 2024 with similar but not identical R-value targets, and Quebec uses CCQ Chapter 1.1 with a separate climate-zone framework. Energy Star New Homes pushes R-70 attics in HDD ≥ 7,000 zones (Yellowknife, Iqaluit, Whitehorse, Yukon).
How many bags of blown insulation do I need for a 1,400 sq ft attic?
A standard 19-pound bag of blown cellulose covers about 30 sq ft installed at R-30 equivalent. Topping up a 1,400 sq ft attic from R-28 to R-60 (a 32-point gap) requires roughly 47 bags at C$17 each, about C$800 in material before equipment rental. Home Depot Canada and RONA lend the blower at no charge with 10+ bag purchases. For blown fibreglass (Owens Corning AttiCat, Johns Manville Climate Pro), coverage at the same R-30 is about 42 sq ft per bag — fewer bags but higher per-bag cost (C$23 typical), so total material cost lands within 5% of cellulose.
Should I top up to R-60 or stop at R-50?
NBC 2020 9.36.2 mandates R-60 for any attic in a climate zone with HDD ≥ 5,000. That includes all major Ontario, Quebec, Manitoba, Saskatchewan, Alberta, NB, NS, NL and PEI cities. Stopping at R-50 violates the code in those zones for any new build, addition, or renovation triggering 9.36.2 compliance. For voluntary upgrades to existing pre-NBC-2020 homes, R-50 still cuts heating loss by 35–45% over a typical R-19 baseline; R-60 adds another 8–12%. The marginal cost of going from R-50 to R-60 is small (~$200 extra in material for a 1,400 sq ft attic), so most NRCan-EnerGuide-rated upgrades target R-60 as the standard.
Can I add insulation on top of existing batts?
Yes — and CRCA's Roofing and Insulation Guide recommends cross-laying new loose-fill blown insulation over existing intact batts as the lowest-cost top-up method. Don't compress the existing batts. Don't bury non-IC-rated pot lights — replace pre-2010 halogen MR16s with IC-rated airtight LED retrofits before blowing, or build a fire-rated dam around them. CSA C22.2 No. 250.0 requires that recessed lights in insulated ceilings carry the 'IC-AT' (insulation contact, air-tight) marking; older lights without it are a fire risk and a major energy bypass when buried.
Does attic insulation qualify for Greener Homes or other Canadian rebates?
The Canada Greener Homes Grant (CGHG) closed to new applicants in March 2024, but pre-approved homeowners still have until March 2027 to complete upgrades. Attic insulation upgrades to NBC 2020 R-60 (or one full R-step above existing) qualified for up to C$1,800 grant. Replacement programs vary by province: BC's CleanBC Better Homes program, Ontario's Save on Energy Home Renovation Savings, Quebec's Rénoclimat, Manitoba's Home Insulation Rebate, and Nova Scotia's Home Energy Assessment all offer C$200–C$2,000 rebates depending on income tier and pre/post EnerGuide score. NRCan EnerGuide for Existing Homes audit (~C$400) is required for most provincial rebates and for the federal interest-free Canada Greener Homes Loan (up to C$40,000 over 10 years).
What insulation works best in a Canadian attic?
Blown cellulose (CertainTeed CelloPak, GreenFiber Sanctuary, IsoFib in Quebec) is the cost-per-R-value champion for top-ups across most Canadian climate zones. R-3.5 per inch installed, low embodied energy, made from 80%+ recycled newsprint. Blown fibreglass (Owens Corning AttiCat, Johns Manville Climate Pro) is non-combustible, doesn't absorb water, and sheds less dust on settle. For deep R-60 to R-70 retrofits in HDD ≥ 7,000 zones, dense-pack cellulose at 3.5 lb/cu ft outperforms loose-fill on convective bypass — worth the 20% premium in arctic climates. For homes with chronic condensation issues (Atlantic coastal, Vancouver Island), Roxul (Rockwool) mineral wool batts or hybrid foam-and-batt assemblies handle moisture better than fibreglass.
What's a vapour retarder and do I need one?
NBC 2020 9.25.4 requires a vapour barrier (typically 6-mil polyethylene sheet, but other Type-1 retarders qualify) on the warm side of the building envelope in zones with HDD > 4,000. For attics, that means under the ceiling drywall, not above the insulation. If your existing ceiling has 6-mil poly under the drywall (most post-1985 Canadian homes do), you don't need an additional vapour barrier when topping up. If you have a vintage plaster-and-lath ceiling with no vapour barrier, NRCan recommends adding a Class III vapour retarder paint to the ceiling drywall before blowing in cellulose — Sherwin-Williams ProMar Vapour Barrier or Benjamin Moore Vapor Barrier 264 both meet ASTM E96 and 9.25.4 Type 3.
Should I air-seal before insulating?
Always. NRCan's EnerGuide audits consistently show that air-sealing the attic floor before insulating delivers 15–35% better whole-house energy savings than insulation alone. Priorities: caulk or low-expansion-foam interior-wall top plates, mastic-seal duct boots and HVAC penetrations, weatherstrip and insulate the attic hatch (NBC 9.25.4 requires sealing of envelope penetrations), and replace pot lights with IC-AT-rated airtight LED retrofits. CRCA also flags ice-dam mitigation: a well-air-sealed attic is the single best defence against ice dams, ahead of even the NBC 9.26.5 ice-and-water shield requirement on the eaves.

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