How much should a roof slope?
How slope is expressed
Slope, or pitch, is the rise in inches for every 12 inches of horizontal run. A 6 in 12 roof rises 6 inches for each foot it runs. You can measure it in the attic or at a gable end with a level held horizontal and a tape measured straight up from the 12-inch mark.
Minimum slopes by material
- Asphalt shingles: 2 in 12 minimum, with double underlayment between 2 in 12 and 4 in 12.
- Clay and concrete tile: 2.5 in 12 minimum, with extra underlayment requirements at lower slopes.
- Lapped metal panels: 3 in 12 without sealant in the laps, or 1/2 in 12 with lap sealant.
- Standing seam metal: 1/4 in 12.
- Membranes such as modified bitumen and single-ply: 1/4 in 12, with tapered insulation or framing to create fall.
These are the minimums in the residential code; manufacturers may require more.
Why steeper often lasts longer
Steeper roofs shed water and debris faster, so shingles stay drier. The trade-off is cost: more roof surface and slower, harness-based work.
Where slope problems hide
Porch roofs, sunroom additions and shed dormers are often built flatter than the main roof, sometimes below what shingles allow. Leaks there are common and are usually fixed by switching to a material suited to the slope. See roof anatomy explained and how roofers measure a roof.