RoofShots Waste Calculation
All major manufacturers describe a “preferred installation method” of a 6 row “stair step method”. This starts with a full shingle and each successive row has an average of 6” cut off to stagger the joint between each successive row. The 7th row starts the cycle again with a full shingle.
With an average 5 5/8” exposure, this creates 1.25 square feet of waste per linear feet of “vertical field edge”. The geometry of hips and valleys lengthens these lines and additional waste is created commensurately.
L = total linear feet of vertical field edge
The waste calculation is simple: L * 1.25
The percentage of waste can be expressed as such:
WASTE % = Area / L * 1.25
NOTE: Waste Considerations
- 1) Manufacturers require a minimum of ¼ - ¾ inches of overhang on the first course.
- 2) Material is wasted on the top row as a full 5 5/8” is not typically needed to reach the ridge.
- 3) This calculation assumes typical W-valley installation (Closed, Woven or California Cut Valley installations will generate additional waste)
- 4) While this calculation is mathematically based & superior to “rules of thumb”, it cannot account for manufacturers defects, poor handling, or inferior installation methods.
- 5) Additional waste must be added for shingles used as starter or hip & ridge cap.