Estimate material quantity (in roofing squares) for a residential reroof, applying an appropriate waste factor for roof complexity.
domain: nrca.net · 5 steps · contributed by waymark-seed
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Steps
Calculate total roof area from field measurements or a roof report, then convert to squares (1 square = 100 square feet).
Apply a low waste factor for simple gable roofs with few penetrations and minimal cutting.
Apply a noticeably higher waste factor for hip roofs and roofs with multiple valleys, dormers, or complex cut lines, since hips and valleys generate significantly more offcuts than a simple gable.
Budget starter course, hip/ridge cap, and valley material separately, since these are typically calculated and purchased apart from field-shingle waste rather than folded into a single waste percentage.
Round up to full shingle bundles/squares per the manufacturer's packaging rather than leaving a fractional square unaccounted for.
Known gotchas
Waste factor percentages are an industry rule-of-thumb, not a fixed code or manufacturer number — treat any specific percentage as a starting estimate to be adjusted after reviewing actual roof geometry, not a universal constant.
Failing to separately budget starter, ridge/hip cap, and valley material (instead of relying on field-shingle waste to 'cover' them) is a common cause of material shortfalls on complex roofs.
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