Roof Area Calculator (Canada)
Free Canadian roof area calculator. Compute actual roof surface in square feet (or square metres) for gable, hip, shed, and L-shape roofs. NBC-aligned guidance for snow and ice and water shield.
Roof Area Calculator
How this Canadian roof area calculator works
Enter the building length and width (in feet or metres — toggle the unit mode), the eave overhang, and the pitch (X/12 or degrees — also toggleable). The calculator returns the actual roof surface area, the rafter length, the slope factor, and an equivalent in roofing squares. Pick the shape — gable, hip, shed or L-shape — and the geometry follows.
It works for any pitch from 1/12 to 21/12, covering low-slope additions, standard suburban houses, and steep Quebec dormered roofs.
The geometry, derived from first principles
The slope factor is the same in every country:
slope factor = sqrt(1 + (rise/run)²) = sec(angle)A 6/12 pitch yields 1.118; an 8/12 pitch 1.202; a 12/12 pitch 1.414. Roof area for a rectangular shape is:
roof area = (length + 2·overhang) × (width + 2·overhang) × slope factorFor a shed (mono-pitch covering the full rectangle) the formula is unchanged. For an L-shape the calculator splits and sums.
Canadian input guidance
- Length × width — measure to the gutter line. Typical Ontario suburban two-storey is 36 × 30 ft; Quebec semi 24 × 32 ft; Calgary bungalow 50 × 28 ft; Atlantic Canada 1.5-storey 28 × 30 ft.
- Pitch — read with a digital pitch app or smart level on the rake of the gable end. NBC Part 9 buildings use 4/12 to 12/12 most commonly.
- Overhang — 12–24 inches typical; 8–12 inches on prairie wind-exposed homes; 24–36 inches on cold-roof assemblies in heavy snow regions.
Canadian pricing context (2026)
Once you have the area, you can budget. Recent Canadian Roofing Contractors Association (CRCA) member quotes, HomeStars and Renomii data give the following 2026 ranges:
| Material | C$ / sq ft installed | C$ / square (100 sq ft) |
|---|---|---|
| 3-tab asphalt shingle (IKO Marathon) | $5.50–$7.50 | $550–$750 |
| Architectural laminate (IKO Cambridge, BP Mystique) | $7.00–$9.50 | $700–$950 |
| Metal shingle (Vicwest, IDEAL Roofing) | $11.00–$15.00 | $1,100–$1,500 |
| Standing-seam steel (Vicwest, Westman Steel) | $13.00–$18.50 | $1,300–$1,850 |
| Concrete tile | $11.00–$15.50 | $1,100–$1,550 |
| TPO / EPDM membrane (low slope, Soprema, Carlisle) | $9.50–$13.50 | $950–$1,350 |
For a 1,800 sq ft surface area at IKO Cambridge architectural shingles ($8.25 / sq ft installed), the contract is roughly C$14,850 ± 15%. Add C$0.40–C$0.60 / sq ft for ice and water shield over the eave band per NBC 9.26.5 and another C$300–C$700 for skip / dumpster.
Common Canadian pitfalls
Quoting from footprint. A 36 × 30 ft footprint at 8/12 looks like 1,080 sq ft but is actually 1,298 sq ft of roof. The 218 sq ft difference is more than 2 squares of shingles.
Forgetting overhang. A 1.5 ft overhang on a 36 × 30 footprint adds 198 sq ft before the slope factor — about C$1,650 of architectural shingle.
Underordering ice and water shield. NBC 9.26.5 requires the membrane from the eave 900 mm beyond the inside face of the exterior wall. On a 6/12 pitch with a 1 ft overhang and 6 in wall, that is roughly 4 ft up the slope. For a 36 ft eave length × 4 ft band × 2 sides = 288 sq ft of self-adhered membrane.
Mixing imperial and metric. Spec sheets from Vicwest use feet; Soprema membrane comes in 1.0 m and 1.5 m rolls. Pick a unit at the takeoff stage and convert once.
Code and standards references
- NBC 2020 (National Building Code of Canada) — Part 9.26 (Roofing) and 9.26.5 (Eave protection / ice and water shield).
- NECB 2020 — National Energy Code of Canada for Buildings; Part 9 thermal envelope minimums (U-value or RSI per climate zone).
- CSA A123.1 / CSA A123.5 — Asphalt shingle physical and aging requirements.
- CSA A123.21 — Standard test method for the dynamic wind uplift resistance of mechanically attached membrane-roofing systems.
- CRCA Roofing Specifications Manual — current best-practice details for sloped and low-slope roofs.
- Provincial codes: Ontario OBC, Quebec CCQ adopt NBC with amendments; BC BCBC; Alberta ABC. All reference the same area calculation method.
Pairing area with the rest of the project
Once you have the surface area, size the structure with the roof truss calculator, price the job with the roof cost calculator, and verify pitch with the roof pitch calculator. For metal reroofs in snow country, also check Vicwest or IDEAL Roofing snow-load tables against your local NBC ground snow load.
The roof area is the foundation number for every Canadian shingling, sheeting and membrane order. Calculate it once, accurately, and the bundles, ice and water shield, drip edge and labour quote all line up.