Typical waste factors
| Roof | Typical waste | Why |
|---|---|---|
| Simple gable, few penetrations | 5–10% | Straight courses, cuts only at rakes |
| Hip roof | 10–15% | Every course is cut at the hips |
| Cut-up roof: valleys, dormers, turrets | 15–20%+ | Many short courses and angled cuts |
Starter strip and hip-and-ridge cap are usually ordered separately by length, not covered by the waste factor.
What drives waste
- Hip and valley length relative to roof area — the strongest single driver.
- Number of planes: more, smaller planes mean more short courses.
- Pitch changes and dormers, chimneys, skylights.
- Material: large-format products (some metal panels, slate) can waste more on cut-up roofs.
How to apply it
Order = roof area × (1 + waste %). A 2,236 sq ft roof at 12%: 2,236 × 1.12 = 2,504 sq ft = 25.1 squares → 26 squares, 76 bundles (at 3 per square, rounded up).
The Roofari app suggests a range from the measured roof’s own edges: total hip and valley length and the number of facets, then lets you set the percentage you use.
Questions
What is a normal waste factor for shingles?
About 10% for an average roof: 5–10% for simple gables, 10–15% for hip roofs, and 15–20% or more for roofs with many valleys and dormers.
Does waste include ridge cap and starter?
Usually not. Hip-and-ridge cap and starter strip are ordered by linear feet of ridge, hip, eave and rake.