Roof pitch is how steep a roof is, written as the rise in inches for every 12 inches of horizontal run. A 4:12 roof rises 4 inches per foot, about 18 degrees; a 12:12 roof rises 12 inches per foot, 45 degrees. Pitch decides which roofing materials are allowed, how much surface the roofer has to cover, how hard the job is to walk, and therefore the price.
How do I measure my roof pitch?
The easiest place is the attic. Hold a level horizontally against the underside of a rafter, mark 12 inches along the level from where it touches the rafter, then measure straight up from that mark to the rafter. That vertical measurement is the rise: 6 inches means a 6:12 pitch.
From outside, hold a 12-inch level horizontally against the roof surface at the edge (from a ladder, carefully) and measure the gap between the far end of the level and the roof. Or stand back and photograph the gable end straight on: the rise over the run of the triangle is the pitch. Phone apps with a tilt sensor laid on the roof or on a rafter give the angle directly.
Pitch in ratios and degrees
| Pitch | Angle | Area factor | Common on |
|---|---|---|---|
| 1:12 to 2:12 | 5 to 9 degrees | 1.00 to 1.01 | Flat and low-slope roofs: membranes only |
| 3:12 | 14 degrees | 1.03 | Low-slope ranchers, additions |
| 4:12 | 18 degrees | 1.05 | 1960s to 80s houses, many Fraser Valley subdivisions |
| 6:12 | 27 degrees | 1.12 | Most 1990s and newer houses |
| 8:12 | 34 degrees | 1.20 | Steeper two-storey homes |
| 10:12 | 40 degrees | 1.30 | Character homes, some new builds |
| 12:12 | 45 degrees | 1.41 | Heritage houses, A-frames, dormers |
The area factor is the multiplier on the roof's footprint. A 1,000 sq ft footprint under a 6:12 roof is about 1,120 sq ft of roofing; under a 12:12 roof, about 1,410. Roofers quote per square foot of surface, which is one reason a steep house costs more to roof than a rancher with the same floor area. The cost guide shows per-square-foot prices for every material.
What's the minimum pitch for each roofing material?
The BC Building Code (and Vancouver's own building bylaw, which uses the same table) sets minimum slopes for houses:
| Material | Minimum slope | Notes |
|---|---|---|
| Asphalt shingles, normal application | 1 in 3 (4:12) | Standard installation |
| Asphalt shingles, low-slope application | 1 in 6 (2:12) | Extra coverage and cemented tabs; BC's roofing association asks for a full self-adhered membrane under shingles between 2:12 and 4:12 |
| Cedar shakes | 1 in 3 (4:12) | |
| Wood shingles | 1 in 4 (3:12) | |
| Profiled metal roofing | 1 in 4 (3:12) | Lower slopes permitted with sealed seams; mechanically seamed standing seam goes to about 2:12 over a continuous membrane |
| Sheet metal shingles | 1 in 4 (3:12) | |
| Clay tile, slate | 1 in 2 (6:12) | |
| Modified bitumen membranes (torch-on) | 1 in 50 up to 1 in 4 | Below 3:12 you need a membrane, not shingles |
Below about 2:12 nothing but a membrane will do, which is why Vancouver Specials and post-and-beam homes have torch-on, TPO or EPDM roofs. Between 2:12 and 4:12 shingles are allowed only with the low-slope method, and many roofers would rather install a membrane or metal there.
How does pitch change the price?
Three ways. More surface, as the table shows. More time, because crews move slower, need more fall protection and more staging as the roof gets steeper, and roofers often add a steep-slope charge above about 8:12. And more waste, because steep, cut-up roofs have more hips and valleys to cut around. Lower Mainland roofers describe steep pitch and difficult access as adding 15 to 40% to a job.
Very low pitches cost more too, for the opposite reason: they need membranes or low-slope methods, and water drains slowly, so the detailing has to be perfect.
Does pitch affect how long a roof lasts?
Yes. Steeper roofs shed water and debris faster, dry sooner after rain and grow less moss. A 4:12 north slope under trees in the Lower Mainland is the hardest place for shingles to survive; a 10:12 south slope is the easiest. Low-slope shingle roofs are the most likely to leak at the edges and valleys, which is why the code demands extra coverage there.
What pitch does a new roof need to be?
Whatever it is now, unless you're changing the structure. Changing a roof's pitch (a flat-to-pitched conversion, or raising a low roof) is structural work that needs a building permit in every Lower Mainland municipality and usually an engineer. See the permit checker. For an ordinary re-roof, the pitch simply decides which materials your roofer can offer: on a 3:12 roof, that's membranes, metal with sealed seams or shingles by the low-slope method; on anything 4:12 or steeper, the full range.
A quick way to estimate your roof area
Measure the house's footprint from outside, including overhangs (typically 1 to 2 feet past the walls on each side). Multiply by the area factor for your pitch. Add about 10% for waste and the ridge, hip and starter courses. A 40 by 28 foot house with 18-inch overhangs under a 6:12 roof: 43 by 31 is 1,333 sq ft, times 1.12 is about 1,490, plus 10% is about 1,640 sq ft, or just over 16 squares. At $5.50 to $9.50 per sq ft for architectural shingles, that's a budget of roughly $9,000 to $15,500 before extras. The roof cost calculator does this arithmetic for you, with tear-off and extras added; a roofer on your roof is still the reliable measure.
Common questions
What's the minimum pitch for shingles?
The BC Building Code allows asphalt shingles down to 1 in 3 (4:12) with normal application, and down to 1 in 6 (2:12) with the low-slope method of extra coverage and cemented tabs. Below that you need a membrane.
How much does pitch add to roof area?
A 4:12 roof has about 5% more surface than its footprint, 6:12 about 12%, 8:12 about 20%, 12:12 about 41%. Roofers price the surface, which is why a steep roof costs more per square foot of house.