The math
A pitched roof has more surface than the footprint under it. The pitch multiplier is √(1 + (rise ÷ 12)²). A 7/12 roof is about 15.8% larger than its footprint; a 12/12 roof is about 41.4% larger.
Checking the carrier’s numbers
- Find total squares and the waste percentage in the roof section of the estimate.
- Compare them with this result. A difference over 5–10% is worth a closer look.
- Look for steep charges (often from 7/12) and high-roof charges for two-story sections.
- Confirm ridge cap, starter, drip edge and ice-and-water shield are listed separately.
Limits of a footprint method
Roofs with several pitches, dormers and valleys need measuring plane by plane. An aerial measurement report or field measurement beats any footprint estimate — use this as a sanity check.
Questions about this tool
What is a square?
100 square feet of roof surface. A typical Illinois two-story home might have 22 to 40 squares.
Why is waste higher on hip roofs?
Hips and valleys need more cutting, so more shingle ends up as scrap. Chicago bungalows with hip roofs often need about 15%.