Estimating a roof from the ground
Measure the footprint of the roof edge (wall dimensions plus overhangs), find the pitch with the roof pitch calculator, and the shingle calculator adds up each roof section at its own pitch and gives you the sloped area, squares, bundles, starter strip, hip and ridge cap, underlayment rolls, drip edge and nails. Then the rainwater tank calculator can size a tank for the rain off that roof. One square is 100 ft², and most shingles come 3 bundles per square. Check the wrapper, because some products cover slightly less (Owens Corning lists 98.4 ft² per square for TruDefinition Duration).
Pitch rules worth knowing
- Asphalt shingles need a slope of at least 2:12 (IRC R905.2.2).
- From 2:12 up to 4:12, double underlayment or a self-adhering membrane is required (IRC; ARMA).
- Pitch multiplier = √(1 + (rise ÷ 12)²). For a 6/12 roof it's 1.118.
Roof work is dangerous. OSHA identifies falls as the leading cause of death in construction, so measure from the ground and leave steep roofs to professionals.