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Eavestrough Slope Calculator

Calculate Canadian eavestrough fall, slope and per-section drop using NBC ¼ in per 10 ft / 2 mm per metre or a custom 1:N ratio. Ice-dam-safe minimums for cold-climate provinces.

Eavestrough Slope Calculator

Calculate Canadian eavestrough fall, gradient and per-section drop using NBC ¼" per 10 ft / 2 mm per m or a custom slope ratio — with ice-dam-safe minimums.

Total fall over run
1.5 in
Slope ratio: 1:480 · Drop per 10 ft: 0.25 in
Effective run (per side): 60 ft · Suggested downspouts: 2
Slope ratio
1:480
Reference standard
NBC 2020 9.26 / CSA B406 — ¼" per 10 ft
Status
Meets NBC / CRCA standard slope

Per-section drop

Distance from high endCumulative drop
10 ft0.25 in
20 ft0.5 in
30 ft0.75 in
40 ft1 in
50 ft1.25 in
60 ft1.5 in

What this calculator does

This calculator answers three questions about Canadian eavestrough slope:

  1. What total fall does my run need? Given a length and a slope rule, what’s the height difference from the high end to the downspout end?
  2. What’s the cumulative drop at every section? A per-10-foot table you can mark on the fascia with a chalk line during install.
  3. Is the slope within Canadian standards? Pass/fail vs the CRCA / CSA B406 practical baseline of ¼ inch per 10 ft (1:480).

It also recommends downspout count based on the rule of one downspout per 35 linear feet of single-pitch run, and lets you toggle between single-pitch and centre-high split-pitch layouts.

How to use it

  1. Set unit mode. Imperial gives feet of run and inches of fall; metric gives metres and millimetres. Both are used interchangeably in Canada — imperial is more common in residential trade language, metric on engineered drawings.
  2. Enter the total eavestrough run length. A typical Canadian two-storey detached home has 160–220 linear feet broken into 4–7 separate runs. This calculator analyses one run at a time.
  3. Pick a layout. Single-pitch is the default for runs under 35 feet. Split-pitch is recommended for runs over 40 feet, especially on long suburban frontages.
  4. Choose a slope rule. Standard (¼ inch per 10 ft, 1:480) is the CRCA practice baseline. Heavy snow (½ inch per 10 ft, 1:240) is the recommended setting for Quebec, Northern Ontario, and Prairie provinces with ground snow load > 2.5 kPa.
  5. Read the result panel. Total fall is the height difference from high end to low end. Slope ratio is reported as 1:N. The per-section table shows cumulative drop every 10 feet.

The per-10-foot drop table

For a 60-foot run at standard ¼ inch per 10 ft:

Distance from high endCumulative drop
10 ft0.25 in
20 ft0.50 in
30 ft0.75 in
40 ft1.00 in
50 ft1.25 in
60 ft (downspout end)1.50 in

Snap a chalk line on the fascia from the high-end gutter top edge to a point 1.5 inches below at the downspout end. Mount K-style hangers every 24 inches along the chalk line.

Single-pitch vs split-pitch in Canadian winter

Single-pitch is one continuous slope from high end to downspout end. Use it for runs up to 35 linear feet.

Split-pitch crowns in the middle and falls to a downspout at each end. The horizontal run stays the same, but each side sees only half the run-length, so the maximum fall is halved. A 60-foot single-pitch run drops 1.5 inches end-to-end; the same 60 feet on split-pitch drops 0.75 inches on each side. The eye reads it as nearly level. Use split-pitch for runs over 40 feet, on long suburban GTA frontages, on Calgary infill where curb appeal matters, and especially in Quebec and Northern Ontario where two drainage paths reduce ice-dam risk on the leeward side.

Code references and standards (Canada)

  • NBC 2020 Section 9.26 — Roofing, references positive drainage and ice-and-water shield 24–36 inches inside the warm wall plane.
  • CSA B406 — Plumbing roof drainage standard, references ECCC IDF tables for rainfall intensity sizing.
  • CRCA Roofing Specifications Manual — practice standard ¼ inch per 10 ft for K-style and half-round eavestrough.
  • Provincial codes — OBC 2024, Quebec Construction Code 2024, BCBC 2024, Alberta Building Code 2023, all adopt NBC verbatim on roof drainage.
  • Provincial licensing — HCRA Ontario, RBQ Quebec, Skilled Trades BC, Alberta Apprenticeship and Industry Training, Saskatchewan Apprenticeship — license requirements for paid installers.
  • Tarion Warranty (Ontario new build), APCHQ Garantie de construction résidentielle (Quebec) — reference CRCA practice standards in their warranty terms.

Cold-climate fall strategy

In Quebec, Northern Ontario (north of Highway 7), Manitoba, Saskatchewan, Alberta, Northern BC, and the territories, install at ⅜ inch per 10 ft (1:320) rather than ¼ inch. Three reasons:

  1. Ice dam mitigation. Steeper slope clears January thaw water before it can refreeze at the cold eave overnight.
  2. Snow load shedding. Heavy wet snow sliding off a steep-sloped roof loads the gutter at the eave; steeper gutter slope drains the meltwater immediately and reduces the gutter sag risk.
  3. Quebec winter premium. Most Quebec contractors price gutter installation 15–25% above Ontario or BC equivalents because of the shorter installation season (May to October only, frozen ground November to April) and the higher technical requirements for ice-dam mitigation. The premium reflects the steeper-slope detail.

In coastal BC (Vancouver, Victoria) and Atlantic provinces (Halifax, Saint John, St John’s), the dominant problem is rainfall intensity rather than ice. Use 3 × 4 inch downspouts and 6-inch K-style eavestrough with the standard ¼ inch per 10 ft slope.

Sources: NBC 2020 Section 9.26; CSA B406; CRCA Roofing Specifications Manual; ECCC IDF rainfall tables; OBC 2024; Quebec Construction Code 2024; HomeStars and Renomii contractor pricing data 2026.

Frequently asked questions

What is the standard eavestrough slope in Canada?
The Canadian residential industry standard, used by the CRCA (Canadian Roofing Contractors Association) and most provincial trade bodies, is ¼ inch of fall per 10 linear feet — 2 mm per metre, or a 1:480 slope ratio. NBC 2020 Section 9.26 references positive drainage without a numerical minimum, but the CRCA Roofing Specifications Manual and CSA B406 explicitly use ¼ inch per 10 feet as the practice standard. In ice-dam-prone provinces (Ontario above Highway 7, Quebec, Manitoba, Alberta, Northern BC), some installers go to ⅜ inch per 10 feet (1:320) to clear melt water faster during January thaws and reduce the volume that can refreeze overnight at the cold eave.
Does Canadian winter affect eavestrough slope requirements?
Yes — cold-climate provinces (Quebec, Ontario north of GTA, Manitoba, Saskatchewan, Alberta, Northern BC, all three territories) typically install at ⅜ inch per 10 feet (1:320) rather than the standard ¼ inch (1:480) for two reasons. First, ice damming is the dominant Canadian eavestrough failure mode — water pools at the eave when warm attic air melts roof snow, then refreezes at the cold gutter. Steeper slope clears melt water before it can refreeze. Second, NBC 2020 Section 9.26.5 requires ice-and-water shield 24 inches inside the warm wall plane (36 inches in zones with ground snow load > 2.5 kPa), and the gutter must drain to that shield's downhill edge — if the slope is shallow, the ice dam forms inside the shield boundary. Quebec and Ontario building inspectors flag insufficient eavestrough slope as part of the Section 9.26 inspection.
How do I check the slope on an existing eavestrough?
Use a 4-foot or 6-foot bubble level and a tape measure. Place the level on the eavestrough's top edge, lift the low end until the bubble centres, and measure the gap. Convert to per-10-foot fall: a 1-inch gap on a 4-foot level means 2.5 inches per 10 feet — way too steep. A 0.1-inch gap means 0.25 inches per 10 feet — the standard. A laser level on the fascia gives sub-millimetre precision. K-style 5-inch eavestrough is the dominant Canadian profile; 6-inch is increasingly common in BC and Atlantic provinces because of higher rainfall intensity (Vancouver coast 60–80 mm/h, Halifax 50–65 mm/h).
Should I use single-pitch or split-pitch on a long Canadian run?
Single-pitch (high at one end, downspout at the other) is the default for runs under 35 feet because it's simpler to set out and only needs one downspout. Split-pitch — high crown in the middle, falling to a downspout at each end — is recommended for runs over 40 feet, common on suburban GTA two-storey detached and Calgary infill. A 60-foot front eavestrough on single-pitch needs 1.5 inches of total fall (visible from the curb); split-pitch on the same run needs only 0.75 inches per side and looks effectively level. The trade-off is one extra downspout, but in Quebec and Ontario the ice-dam mitigation benefit of two drainage paths often pays for the extra downspout in the first thaw cycle.
How many downspouts does my Canadian eavestrough run need?
Rule of thumb: one downspout per 35 linear feet of single-pitch eavestrough, or per 40 feet on split-pitch. CSA B406 sizes downspouts from rainfall intensity (Environment and Climate Change Canada IDF tables for your municipality, 5-minute duration) and roof drainage area. For typical Canadian housing in 5-inch K-style at ¼ inch per 10 ft, 35 feet per 2 × 3 inch downspout is the safe rule. In high-rainfall coastal BC (Vancouver, Victoria, North Vancouver), upsize to 3 × 4 inch downspouts and reduce spacing to 25 feet. In Quebec winter, add a downspout extension that can be removed before snow load builds at the splash block. Pair this calculator with our gutter size calculator for the formal CSA method.
Why does my eavestrough overflow even though it has slope?
Three usual causes. First, undersized downspout — a 2 × 3 inch downspout drains roughly 600 sq ft of roof, while a 3 × 4 inch downspout drains 1,200+ sq ft. If your roof tributary area exceeds capacity at your municipality's IDF rainfall intensity, water backs up regardless of slope. Second, slope is correct but the eavestrough has sagged between hangers (more common in Ontario freeze-thaw cycle areas) — every 32 inches should be straight. Third, the downspout is clogged at the elbow or in the underground tie-in. Maple, oak, and white pine are the dominant eastern Canadian eavestrough litter; spring and autumn cleaning is mandatory.
Can I retrofit slope into an existing dead-level eavestrough?
Yes. Pop the eavestrough off its hangers, remove every other hanger, snap a chalk line on the fascia from the high end to a point N inches below at the downspout end (where N = run length × 0.025 inch per foot for ¼ inch per 10 ft fall), and refit. Reposition hangers every 24 inches along the chalk line. Budget 4–6 hours for a 60-foot run for a competent DIYer, or C$320–C$560 paid labour. In Quebec, gutter retrofits during winter are not recommended — the metal becomes brittle below -15°C and pop rivets fracture under impact. Wait until April thaw or do the work in October before the deep freeze. Note that in Quebec, gutter installation by a paid contractor is licensed work under the RBQ if the project value exceeds C$3,000.
Is eavestrough slope a building-code requirement in Canada?
NBC 2020 Section 9.26 and CSA B406 reference 'positive drainage' without specifying a slope number. Provincial codes — Ontario Building Code (OBC) 2024, Quebec Construction Code, BC Building Code 2024, Alberta Building Code 2023 — generally adopt NBC verbatim on this point. So slope is not a numerical code requirement, but the CRCA Roofing Specifications Manual (referenced by Tarion Warranty in Ontario, RBQ in Quebec, Skilled Trades BC in BC) treats ¼ inch per 10 ft as the practice standard. Manufacturer warranties (IKO, BP Canada, GAF Canada, Owens Corning Canada) and most homeowners insurance policies require manufacturer-specified slope as part of the warranty terms. Ignoring the standard can void warranty coverage on roof products that include eavestrough as part of the assembly.

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