Why ten percent waste is wrong for most roofs
<Assets TBC> A simple gable roof beside a hip roof with dormers and valleys
Ten percent is the waste factor most estimates use. A plain gable roof wastes less than that. A roof with several valleys, dormers and hips wastes more.
Waste comes from cuts. Every valley, hip and rake turns part of a shingle into scrap, and short runs make it worse because the offcut from one course is less likely to start the next.
RoofTools will set the waste factor from the roof itself: the length of its valleys and hips and the length of its runs. It is in development.