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Shed Roof Rise Calculator

Calculate the rise of a shed roof from span and pitch (X/12 or degrees), or work backwards from a target rise. Returns rafter length, slope factor, and surface multiplier to NBC 2020.

Shed Roof Rise Calculator

Calculate from:
Rise (ft)
3
Angle
14.04°
Pitch
3/12
Rafter length (ft)
13.4
Slope factor
1.031
Multiply footprint area by this for true roof surface area.

What this calculator does

This tool computes the vertical rise of a Canadian shed (mono-pitch, skillion, or lean-to) roof from the span and either the pitch in X/12, the angle in degrees, or a target rise. It returns the rise, the slope angle, the equivalent X/12 pitch, the rafter length (including eave overhang), and the slope factor — the multiplier you apply to the building footprint to get the true roof surface area.

Imperial and metric inputs are both supported, and the X/12 convention is preserved for consistency with NBC and provincial framing references.

How shed roof math works

A shed roof is a right triangle in section — the horizontal leg is the span, the vertical leg is the rise, and the hypotenuse is the rafter length before overhang. The relationships are:

  1. Rise = span × (pitch/12) when working from X/12 pitch.
  2. Rise = span × tan(angle) when working from degrees.
  3. Pitch = (rise/span) × 12 in X/12 form.
  4. Slope factor = sqrt(1 + (rise/span)²) — multiply footprint area by this for actual roof area.
  5. Rafter length = (span + overhang) × slope factor — total rafter material per piece.

The slope factor matters because asphalt shingle bundles, underlayment rolls, and metal panel pricing are quoted per square (100 sqft) of actual roof surface, not per square foot of building footprint.

Reference test cases

SpanPitchOverhangRiseAngleRafter lengthSlope factor
12 ft3/1216 in3.00 ft14.04°13.74 ft1.031
10 ft2/1212 in1.67 ft9.46°11.15 ft1.014
16 ft4/1224 in5.33 ft18.43°18.97 ft1.054
12 ft6/1216 in6.00 ft26.57°14.91 ft1.118

The first row is the canonical Ontario/Quebec backyard storage shed at 3/12 — common because that pitch sheds Toronto/Montreal snow loads reliably with 2x10 SPF #2 rafters and accepts ribbed metal panels (Vicwest CL Trimrib, Ideal Roofing Heritage, Westform Metals Tuff-Rib).

Materials and minimum slopes

NBC 2020 Subsection 9.26 minimum slopes for shed roofs in Canada:

  • 1/50 (0.5° / 0.25/12) — Fully adhered single-ply membranes (TPO, EPDM, PVC) per 9.26.4.6.
  • 1/12 (4.8°) — Cold-applied modified bitumen and built-up roofing (BUR).
  • 2/12 (9.5°) — Through-fastened metal panels with sealant tape in laps (CSSBI 10M-08).
  • 3/12 (14°) — Standing seam metal with concealed fasteners (CSSBI 10M-08).
  • 4/12 (18.4°) — Asphalt shingles per 9.26.7.1; below 4/12 down to 2/12 requires self-adhered membrane underlayment over the entire roof area.

For a backyard storage shed in southern Ontario, a 3/12 ribbed metal roof costs about C$5.00 to C$8.50 per square foot installed (Q1 2026 retail pricing at Home Depot Canada and Rona for 28 gauge G90 painted galvanized panels in Charcoal or Burnished Slate). A 4/12 architectural asphalt shingle roof on the same shed runs C$4.50 to C$7.50 per square foot installed for IKO Cambridge or Owens Corning ProEdge. Quebec winter premium adds 15-25% for labour from November through March.

Code references

  • NBC 2020 Part 9 — Housing and Small Buildings.
  • NBC 2020 §4.1.6 + Tbl C-2 — Climatic and seismic information for over 700 Canadian locations.
  • NBC 2020 §9.23 — Wood-frame construction.
  • NBC 2020 §9.26 — Roofing.
  • NBC 2020 §9.26.6.2 — Ice and water shield requirements at eaves.
  • CSA O86:24 — Engineering design in wood.
  • CSSBI Standard 10M-08 — Steel building roofing systems.
  • CRCA Roofing Specifications Manual 2022 — Canadian Roofing Contractors Association reference.
  • Provincial codes — Ontario Building Code (OBC) 2024, Quebec CCQ, BCBC 2024, Alberta Building Code 2023, Manitoba Building Code, Saskatchewan Building Code, Maritime Provinces Atlantic Building Code.

Practical notes for Canadian shed roofs

Snow load by province. NBC 2020 Table C-2 gives ground snow load Ss and rain-on-snow Sr for over 700 Canadian locations. Toronto Ss 1.4 kPa, Ottawa 2.4, Montreal 2.6, Quebec City 4.4, Saguenay 5.0, Halifax 2.4, St John’s 4.0, Winnipeg 1.9, Regina 1.0, Calgary 1.1, Vancouver 1.6, Whistler 7.0, Yellowknife 1.7, Iqaluit 1.4. The Snow Load Calculator handles the full NBC §4.1.6 method — pf = 0.8 × Ss × Cw × Cs × Ca × Cb.

Ice damming and eave protection. NBC 9.26.6.2 mandates self-adhered membrane (peel-and-stick like Owens Corning WeatherLock G, IKO StormShield, Grace Ice & Water Shield, Henry Blueskin RF200) from the eave to at least 12 inches (300 mm) inside the warm wall. In practice this means 36 inches (914 mm) of ice and water shield at the eave for typical shed roofs. Quebec, Maritimes, and northern Ontario specs often require 48 inches (1219 mm) for severe icing exposure.

Quebec winter premium. The CCQ (Commission de la Construction du Québec) and RBQ (Régie du bâtiment du Québec) recognize a winter premium of 15-25% on framing labour from approximately November 15 to March 15, when heated enclosures, frost-protected concrete cure, and limited daylight reduce productivity. Budget for the premium when scheduling shed builds in Quebec, northern Ontario, and Maritime provinces.

Wind uplift in coastal regions. Coastal British Columbia (Vancouver Island, Tofino, Prince Rupert) and Atlantic Canada (St John’s, Halifax, Saint John, Charlottetown) carry hourly wind speeds 30-45 m/s per NBC Table C-2. Use ring-shank or screw-shank nails per NBC 9.23.3.4, and follow CSSBI 10M-08 perimeter fastener density schedules — typically 6-inch (150 mm) on-centre at perimeter zones, 12-inch (300 mm) field.

Ventilation. NBC 2020 9.19.1.2 requires roof venting at 1/300 ratio with a Class I vapour retarder under the ceiling, or 1/150 without. Shed roofs vent at the eave (intake) and ridge or upper-eave (exhaust). Use the Roof Vent Calculator to size both.

Incentives and rebates

  • Canada Greener Homes Loan — Up to C$40,000 interest-free financing for energy retrofits including upgraded roof insulation when paired with the Attic Insulation Calculator recommendations.
  • Quebec Programme Rénoclimat — Grants up to C$2,500 for attic and roof insulation upgrades.
  • BC CleanBC Better Homes — Rebates for envelope upgrades meeting Step Code 3+ thermal performance.
  • Ontario Save on Energy — Enbridge Home Efficiency Rebate Plus and IESO Save on Energy programs.

Sources and authority data

  • CRCA (Canadian Roofing Contractors Association) — Roofing Specifications Manual 2022 edition.
  • CASMA (Canadian Asphalt Shingle Manufacturers Association) — Underlayment and ice-and-water shield specifications.
  • HomeStars 2026 — Backyard storage shed cost data, C$25 to C$85 per square foot turn-key.
  • Renomii 2026 — Lean-to addition cost data, C$2,800 to C$8,500 for a 10 × 12 ft attached shed roof.
  • Home Depot Canada, Rona, Lowes Canada, Patrick Morin (Quebec) — Q1 2026 retail pricing for SPF framing, ribbed metal panels, ice and water shield, and architectural shingles.
  • Vicwest, Ideal Roofing, Westform Metals — Canadian metal roof panel manufacturers with cold-climate fastening schedules.

Frequently asked questions

What is a typical shed roof pitch in Canada?
Most Canadian residential shed roofs sit between 1/12 and 6/12. NBC 2020 Subsection 9.26 references roof covering minimum slopes that mirror IRC R905: 1/12 (4.8°) for fully adhered single-ply membranes and modified bitumen, 2/12 (9.5°) for sealed-lap metal panels, 3/12 (14°) for unsealed lap metal, and 4/12 (18.4°) for asphalt shingles. Quebec's CCQ adds requirements for ice and water shield to 36 inches inside the warm wall (NBC 9.26.6.2). For a backyard storage shed in Ontario or Quebec, a 3/12 pitch is the most common compromise — it sheds snow reliably under Toronto/Montreal climate loads and accepts low-cost ribbed metal.
How do I calculate the rise on a shed roof from span and pitch?
Multiply the span by the pitch fraction. For a 12 ft (3.66 m) span at 3/12 pitch, the rise is 12 × 3/12 = 3 ft (0.91 m). To convert pitch to angle, take the arctangent: atan(3/12) = 14.04°. The rafter length along the slope is span × sec(angle), and the slope factor (multiplier from footprint to true roof area) is sec(angle) = 1/cos(angle), or equivalently sqrt(1 + (rise/span)²). For 3/12 pitch the factor is 1.031, so a 12 × 16 ft shed has 192 sqft of footprint and 197.9 sqft of roof surface.
What is the minimum slope for a shed roof under the National Building Code?
NBC 2020 Subsection 9.26.4 sets minimum slopes by covering type. Fully adhered single-ply membrane (TPO, EPDM, PVC) and SBS-modified bitumen go to 1/50 (0.5° or about 0.25/12), but most Canadian designers use 1/12 minimum for cold-climate construction because of snow drifting and ice damming. Asphalt shingles need 1/3 minimum slope (4/12) per NBC 9.26.7.1 unless a self-adhered membrane underlayment is installed for the entire roof area, in which case 1/6 (2/12) is permitted. Standing seam metal goes to 1/24 (0.5/12) per CSSBI Standard 10M-08.
How does eave overhang affect the rafter length?
The overhang adds to the horizontal distance, so the rafter material grows in the same slope ratio. For a 12 ft span at 3/12 with a 16 inch tail, the rafter length is (12 + 1.33) × sqrt(1 + (3/12)²) = 13.33 × 1.0308 = 13.74 ft. NBC 9.26.6.2 requires ice and water shield (self-adhered membrane) from the eave inward to a point at least 12 inches (300 mm) inside the warm wall — this typically means 36 inches (914 mm) of ice and water shield from the fascia inward. CRCA Roofing Specifications Manual 2022 recommends 24 inch (610 mm) minimum overhang in Quebec, Maritimes, and northern Ontario to keep ice dams away from the wall face.
What is the slope factor and why does it matter for shed roofs?
The slope factor is sec(angle), or equivalently sqrt(1 + (rise/run)²). For 1/12 it is 1.003, for 2/12 it is 1.014, for 3/12 it is 1.031, for 4/12 it is 1.054, for 6/12 it is 1.118, for 12/12 (45°) it is 1.414. Multiply the building footprint by this factor for true roof surface area. A 12 × 16 ft shed at 4/12 pitch has 192 sqft of footprint and 202.4 sqft of roof, or about 2 squares of asphalt shingles (Owens Corning ProEdge, GAF Timberline NCA, IKO Cambridge). Bag and bundle quantities scale on the slope-factored area, not the footprint.
Can I build a shed roof in a high-snow region of Canada?
Yes, but NBC 2020 §4.1.6 and Table C-2 of Division B impose much heavier loads than mid-latitude US designs. Quebec City carries a ground snow load Ss of 4.4 kPa (about 92 psf), Saguenay 5.0 kPa (104 psf), and Whistler BC up to 7.0 kPa (146 psf). For a shed roof at 3/12 pitch in Quebec City under Ss = 4.4 kPa: pf = 0.8 × Ss × Cw × Cs × Ca × Cb = 0.8 × 4.4 × 1.0 × 1.0 × 1.0 × 1.0 = 3.52 kPa = 73.5 psf. That is more than double a Boston design and typically requires 2x12 SPF rafters at 16 inch centres for a 12 ft span. Use the [Snow Load Calculator](/calculators/snow-load-calculator/) for the full NBC 9.4 method.
What rafter size do I need for a shed roof span?
NBC 2020 9.23.4.2 references CSA O86 design tables. For SPF #2 rafters at 16 inch centres under 30 psf snow load (1.4 kPa, equivalent to southern Ontario): 2x6 to 10 ft 4 in, 2x8 to 13 ft 8 in, 2x10 to 17 ft 5 in, 2x12 to 21 ft 1 in. Quebec winter snow zones (Ss 3.0-5.0 kPa) reduce these spans by 25-40 percent — a Quebec City 12 ft span at 3/12 needs 2x10 SPF #2 minimum. Doug fir-larch adds about 12 percent to allowable spans. The [Roof Rafter Calculator](/calculators/roof-rafter-calculator/) handles species, snow zone, spacing, and bearing length for all NBC climatic data Table C-2 cities.
How do I find the high-wall stud height for a shed roof?
The high-wall stud is the low-wall stud height plus the calculated rise. For a low wall with 92-5/8 in (2353 mm) studs and a 12 ft span at 3/12 pitch, the rise is 36 inches (914 mm). High-wall studs cut at 92-5/8 + 36 = 128-5/8 in (3267 mm). The high-wall top plate sits at the rafter slope — for a plumb-cut shed the plate is level and the rafter bird's mouth seats on it directly. Quebec winter premium for framing labour runs 15-25% from November through March because heated enclosures are typically required to keep adhesives and concrete viable below -10°C — see RBQ guidance for cold-weather construction.

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