Ten percent for a simple gable with no valleys, twelve with dormers, fifteen for a hip roof and up to twenty for a complex roof with several valleys and planes. It is set by the roof's shape, not by how careful the crew is — every diagonal cut leaves an unusable offcut.
The Waste Factor Calculator recommends the correct overage percentage to add to your shingle order based on roof complexity. Simple gable roofs use 10%, hip roofs 12-15%, and cut-up roofs with multiple valleys, dormers, and skylights need 15-20% or more. Enter your roof type and pitch and the tool returns the recommended waste factor and the additional bundles to order. Underestimating waste means a return trip to the supply yard mid-job — overestimating ties up cash.
Waste factor is the percentage added to the measured roof area to cover cuts, offcuts and mistakes. Getting it wrong in either direction costs money — too low means a second delivery, too high means bundles you cannot return once opened.
| Roof type | Waste | 2,000 sq ft becomes | Extra squares |
|---|---|---|---|
| Simple gable, no valleys | 10% | 2,460 sq ft | 2.2 |
| Gable with dormers | 12% | 2,504 sq ft | 2.7 |
| Hip roof | 15% | 2,571 sq ft | 3.4 |
| Cut-up hip with valleys | 18% | 2,639 sq ft | 4 |
| Complex, many planes | 20% | 2,683 sq ft | 4.5 |
Areas shown are the sloped area of a 2,000 sq ft footprint at 6/12 pitch.
Pick the figure from the shape of the roof, not from how careful you intend to be. A simple gable with two planes and no valleys genuinely does run at 10%. Add dormers and it is 12%. A hip roof, where every one of the four planes has two diagonal cuts, runs 15%. A cut-up roof with several valleys, a cross gable and a couple of dormers reaches 18% to 20%, and that is not sloppiness — it is geometry.
Under-ordering costs more than over-ordering. Unopened bundles usually go back for credit; a second delivery for four bundles costs a trip charge and stops the crew for half a day.
Ten percent for a simple gable, twelve with dormers, fifteen for a hip roof and up to twenty for a complex roof with several valleys and planes.
Every hip is a diagonal cut down the length of the roof, and each cut produces an offcut too small to use elsewhere. More planes means more edges means more waste.
Slightly over. Unopened bundles can often be returned, but a second delivery for three bundles costs a trip charge and a day of lost work.
To underlayment yes, though a smaller figure is usually enough because it is cut less. Nails do not need a waste factor in the same sense, but buy roughly 10% over anyway — guns misfire and coils jam, and leftover roofing nails keep indefinitely.