The math behind it
A roof is larger than the footprint underneath it, and the gap grows with pitch. The pitch multiplier is √(1 + (rise ÷ 12)²). An 8/12 roof is about 20% larger than its footprint. A 12/12 roof is about 41% larger.
Checking the carrier’s roof section
- Compare total squares and the waste percentage with your result. Differences over 5–10% are worth a closer look.
- Check that tear-off includes every existing layer. Older homes often have two.
- Look for steep charges, usually from 7/12 or 8/12 up, and high-roof charges on two-story sections.
- Confirm starter, ridge, drip edge, ice barrier at the eaves and ventilation are listed.
Limits of a footprint estimate
Roofs with several pitches, dormers and valleys need to be measured plane by plane. Treat this as a check, not a substitute for a field or aerial measurement.
Questions about this tool
What is a roofing square?
100 square feet of roof surface. Many New Jersey colonials and split-levels have roughly 18 to 35 squares.
Why does the number of layers matter?
Each existing layer must be removed and disposed of before the new roof goes on. Missing tear-off is a common gap in roof estimates.