Roof pitch is the steepness of a roof, expressed as a ratio of vertical rise to horizontal run (e.g. 6/12 means 6 inches of rise per 12 inches of run).
Pitch affects material choice (very low-slope roofs need membrane systems rather than shingles), water shedding speed, attic space, and installation labor cost — steeper roofs require more safety equipment and take longer to work on, which shows up directly in contractor quotes. A 4/12 to 8/12 pitch is considered a standard, moderate slope for most residential shingle roofs.
Most manufacturers require a minimum 2/12 or 3/12 pitch for standard asphalt shingles, sometimes with additional underlayment requirements below 4/12 — anything lower needs a flat/low-slope membrane system instead.
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