Roofers price work in squares, and one square is one hundred square feet of roof surface.
At a glance
- Pitch is rise over twelve inches of run.
- Steep roofs cost more because the work slows down.
- Roof area is always larger than floor area.
- Waste factor covers cuts, and ten percent is normal.
Reading pitch
A 4 in 12 pitch rises four inches for every twelve inches across. Anything at 2 in 12 or less counts as low slope and needs a membrane rather than shingles. Anything over 8 in 12 needs staging and safety gear, which raises the price.
You can guess the pitch from the street by comparing the roof line to a level, but a roofer measures it with a pitch gauge in the attic or on the surface.
Turning floor area into roof area
Roof surface is the footprint times a pitch multiplier. A 4 in 12 roof multiplies by about 1.06. An 8 in 12 multiplies by about 1.20. A 12 in 12 multiplies by about 1.41.
So a 2,000 square foot footprint at 6 in 12 gives roughly 2,240 square feet of roof, or about 22 and a half squares before waste.
Waste and why bids differ
Every hip, valley and dormer forces cuts, and the offcuts get thrown away. A simple gable roof runs about 8 percent waste. A cut up roof with several valleys runs 15 percent or more.
When two bids differ, ask each one for the square count and the waste factor. That single question explains most gaps.
Common questions
How do roofers measure without climbing
Aerial measurement reports and satellite tools are common now and are accurate within a few percent.
What pitch can shingles go on
Down to 2 in 12 with a doubled underlayment, though 4 in 12 and up is the normal range.
Why is my small roof so expensive
Setup, disposal, permits and crew time do not shrink with the roof.