Eave protection in Canada: measuring ice and water shield to the code
Canada's code sends eave protection 900 mm up the slope and 300 mm past the inner wall. How to measure that in feet and inches, the exemptions, and a worked example.
In Canada, the National Building Code (Sentence 9.26.5.1) calls for eave protection on shingle, shake and tile roofs that runs at least 900 mm (35.4 in) up the slope from the roof edge, and at least 300 mm (11.8 in) past the inner face of the exterior wall. Whichever of those two lines sits higher up the roof sets your membrane width. Everything else is measuring the eaves, the overhang and the wall.
Your province adopts its own edition, so treat these numbers as the national baseline and check the one that applies to the job.
What the Canadian code asks for at the eaves
The APCHQ guide to the rule (written for Québec, which follows the same article) reads it as two conditions on the same strip of membrane:
- It starts at the roof edge and climbs at least 900 mm along the slope.
- It reaches a line at least 300 mm inside the inner face of the exterior wall.
The first is a floor. The second grows the strip on a deep overhang or a thick wall.
The APCHQ guide adds two points worth keeping. If the shingle maker's instructions ask for more than the code, the stricter requirement wins. And a code exemption doesn't stop you from protecting the eaves anyway; with winter thaw-and-rain cycles, the guide calls eave protection good practice whatever the slope.
Which roofs are exempt in Canada
The NRC commentary on the national code (an earlier edition, archived, but the list matches the APCHQ guide) exempts eave protection:
- over unheated garages, carports and porches
- where the distance from the roof edge to the inner face of the exterior wall, measured along the slope, exceeds 900 mm
- on asphalt shingle roofs installed under Subsection 9.26.8 of the code
- on roofs with a slope of 1 in 1.5 (8/12) or steeper
- in regions with 3,500 or fewer degree-days (the APCHQ guide notes there are none in Québec)
Two of those are measurements, which is why you can't skip the overhang. An attached garage that's heated is not an unheated garage. And code-exempt is not warranty-exempt: check the shingle maker's application instructions before you leave the membrane off.
How to measure the membrane width
You need three numbers per eave, plus the pitch:
- Overhang: horizontal distance from the roof edge (drip edge) to the outside face of the wall.
- Wall thickness: outside face to inner face. Cladding, sheathing, studs and drywall all count; measure it at a window opening or take it from the plans.
- Eave length: lineal feet of every eave edge on the roof.
- Pitch factor: 4/12 1.054, 6/12 1.118, 8/12 1.202.
Then, along the slope:
- Edge to inner wall = (overhang + wall) × pitch factor. If this is over 35.4 in (900 mm), the overhang exemption may apply.
- Required width = the larger of 35.4 in, or (overhang + wall + 11.8 in) × pitch factor.
Converting the 300 mm to slope with the rest is the conservative reading: a slightly wider strip, never a narrower one.
Worked example: a Canadian two-storey in Ontario
A two-storey gable in Ontario, 6/12 pitch, 40 ft of eave on the front and 40 ft on the back, so 80 lin ft of eave. The rakes don't take eave protection under this rule.
- Overhang: 16 in horizontal
- Wall: 7.5 in from siding to drywall
- Edge to inner wall: (16 + 7.5) × 1.118 = 26.3 in along the slope (668 mm). That's under 35.4 in, so no overhang exemption. The pitch is under 8/12, so no slope exemption either.
- Required width: (16 + 7.5 + 11.8) × 1.118 = 35.3 × 1.118 = 39.5 in, which beats the 35.4 in floor. The strip must reach 39.5 in up the slope.
A single course about 36 in wide falls short by 3.5 in, so you run two courses. With an example side lap of 3 in between courses (use the lap on your membrane's label), two courses cover 36 + 36 − 3 = 69 in, comfortably past 39.5 in.
Material
- Roll length needed: 80 lin ft × 2 courses = 160 lin ft
- Area: 160 × 3 ft = 480 ft²
- Rolls, using an example roll length of 65 ft (check your product's label): 160 ÷ 65 = 2.5, so 3 rolls, before end laps and valleys
Now push the same house to an 8/12 pitch and the code exemption for slope applies. Or widen the overhang to 30 in at 6/12: (30 + 7.5) × 1.118 = 41.9 in (1,065 mm) along the slope, over 900 mm, so that eave is exempt under the national wording. In both cases read the shingle maker's instructions before you take membrane off the order.
Ordering eave protection in Canada
This rule covers the eaves. Valleys, low-slope sections, crickets and walls follow the shingle maker's instructions; measure them as separate lines:
- Eaves: eave length × number of courses
- Valleys: valley length, one strip each
- Other details: as the manufacturer specifies
If you'd rather not do the arithmetic by hand, the free ice and water shield calculator takes the pitch, overhang, wall thickness and eave length and returns courses and rolls. Set Coverage inside the wall to 12 in (300 mm) for the national rule, and check the slope distance against the 35.4 in floor. For reading overhangs off imagery, see measuring overhangs and eaves from aerial imagery.
Provincial building codes across Canada
The national code applies once a province or territory adopts it. Ontario has the Ontario Building Code, British Columbia the BC Building Code, Alberta its own edition, Québec the Code de construction. Editions, dates and local amendments differ, and municipalities enforce them. Before you quote the membrane, check the edition that applies at that address, and how the local inspector reads it.
Where you trip
Measuring the overhang along the slope, then multiplying again. Take the overhang and wall horizontally, add them, then apply the pitch factor once.
Forgetting the wall. The 300 mm is measured past the inner face. A 2×6 wall with siding is several inches you have to cover.
Calling a heated garage "unheated". The exemption is for unheated garages, carports and porches. A bonus room over the garage changes the answer.
Assuming exempt means none. The shingle maker can require more than the code, and the stricter rule applies.
How RoofStruct handles the eaves
RoofStruct is free, unlimited self-serve measuring and PDF reports, no card. You trace the roof on satellite imagery or your own drone or phone photo, label each edge, and the eave length comes out with the other edge totals. Settings › Localization › Measurement Units switches Imperial (ft, ft²) and Metric (m, m²) and carries into exports. The free pitch finder gets the pitch from a Canadian address. Overhang and wall thickness still come from the site or the plans.
FAQ
How far up the roof does eave protection go in Canada?
Under the national code, at least 900 mm (35.4 in) up the slope from the roof edge and at least 300 mm (11.8 in) past the inner face of the exterior wall, whichever reaches higher. Check your province's edition.
Is ice and water shield required on an 8/12 roof in Canada?
The national code exempts roofs with a slope of 1 in 1.5 or steeper, which is 8/12. The shingle maker may still require it, and the stricter requirement applies.
Do I need eave protection on a garage?
Not over an unheated garage, carport or porch under the national code. A heated or finished garage doesn't qualify for that exemption.
Does a wide overhang change the rule?
Yes, two ways. A deeper overhang pushes the 300 mm line higher, so you need more membrane. Past 900 mm from the edge to the inner wall face along the slope, the national code exempts the eave.
Sources
Checked Oct 2026: