New Zealand · metal roofing
Roofing waste calculator
A flat 10% is how hip roofs run short and simple gables get over-ordered.
Gable longrun, sheets ridge-to-eave, no valleys: the per-plane round-up already is the waste on the sheets. A 5% area allowance covers handling damage and a colour-batch spare, not geometry.
Hip roofs throw diagonal offcuts that rarely restock as a full sheet. This calculator starts hips at 12% of sloped area when converting area to sheets. Each valley adds 3%. Pitches of 35° and over add 2% because cuts get nastier and more sheets get walked on.
Waste is not flashing. Ridge, barge, hip and valley are measured as lineal metres on top of the sheet order. Do not hide them inside the waste percentage.
FAQ
Can I turn waste off?
Yes — set an override percentage. Use 0% if you are only checking geometry. Do not order from a 0% hip takeoff.
What about dormers and penetrations?
Not modelled. Add a valley count as a blunt instrument, or add a separate section. Skylights and chimneys still need soakers and extra sheet.