How Roof Pitch Is Measured
Pitch is written as a ratio of rise over run. The run is always 12 inches, and the rise is how many inches the roof climbs over that 12-inch span. A 4:12 roof rises 4 inches for every foot, while a 9:12 roof rises 9 inches over the same distance and feels noticeably steep underfoot.
Roofers group pitches into general categories:
- Low slope: below 3:12, which usually requires special membranes rather than standard shingles.
- Conventional slope: roughly 4:12 to 9:12, the most common range for homes and ideal for asphalt shingles.
- Steep slope: 10:12 and above, often found on chalets and older homes with dramatic rooflines.
Why Pitch Matters in the Inland Northwest
In the Spokane and North Idaho climate, pitch is not just a style choice; it directly affects how your roof handles our long winters. A steeper roof sheds snow and water faster, which reduces the standing load from heavy snowfall and lowers the odds of leaks during freeze-thaw cycles.
Low-slope roofs hold snow longer, giving meltwater more time to refreeze at the cold eaves. That refreezing is what forms ice dams, the ridges of ice that back water up under your shingles. Steeper pitches help water run off before it has a chance to refreeze, though no pitch is immune without proper insulation, ventilation, and ice-and-water shield at the eaves.
How Pitch Affects Materials and Cost
Your pitch decides which roofing materials will actually perform on your home. Standard asphalt shingles are rated for roofs at or above 2:12, but they need extra underlayment between 2:12 and 4:12. Below 2:12, you generally need a sealed membrane system instead of shingles.
Pitch also affects labor and price. Steeper roofs require more safety equipment, slower work, and more material to cover the larger surface area, so they typically cost more to install. Knowing your exact pitch is an important first step when planning a roof replacement and choosing materials built for our weather.
Finding Your Own Roof's Pitch
You can estimate pitch from inside the attic with a level and a tape measure: hold the level horizontal against a rafter, measure 12 inches along it, then measure straight down to the rafter. That vertical measurement is your rise over a 12-inch run.
For an accurate, safe assessment, though, it is best to have a professional measure it as part of an inspection. If you are unsure of your pitch or weighing your options, request a free estimate and we will measure it for you and recommend the right system for your home.