01
Separate types of allowance
Calculate field quantity first, then consider starter and top courses, hips, valleys, rakes, penetrations, breakage, sorting rejection, color distribution and attic stock.
02
Complexity changes the number
Small roof planes, diagonal cuts, turrets, random widths and patterns create more offcuts. Some cut pieces can be reused elsewhere, but only when size, holes and quality remain suitable.
03
Protect future matching
Retain labeled full pieces from the exact production lot. Future availability is uncertain, and a small attic stock can prevent visually poor repairs years later.