How much pitch should a lean-to roof have?
Short answer. A lean-to roof should have at least the minimum slope its roofing material allows, and a little more is better: asphalt shingles need at least 2 in 12 (with double underlayment up to 4 in 12), lapped metal panels without sealant need 3 in 12, and roll roofing needs at least 1 in 12. For most sheds, porches and lean-to additions, a pitch of about 3 in 12 to 4 in 12 is a practical target that drains well and keeps the low end above door and window heads.
Code minimums by roofing material
- Asphalt shingles. 2 in 12 minimum. Between 2 and 4 in 12, the International Residential Code requires two layers of underlayment or an equivalent membrane.
- Lapped metal panels. 3 in 12 without applied lap sealant; as low as one half in 12 with sealant in the laps.
- Standing seam metal. As low as one quarter in 12.
- Mineral-surfaced roll roofing. 1 in 12 minimum.
- Membrane roofing. For near-flat roofs, about one quarter in 12, with a proper low-slope system.
Always check the product's own installation instructions, which can be stricter than code.
Practical design tips
- Mind the low end. On a lean-to attached to a house, the high side sits under the existing eave or against the wall, and the low side must clear doors, windows and headroom. That geometry often decides the pitch.
- Flash the wall connection. Where the lean-to meets a wall, use step flashing or a continuous wall flashing tucked behind siding, and a kickout flashing at the bottom.
- Plan for water. A gutter at the low edge keeps runoff off foundations and walkways.
- Georgia rain. Low slopes drain slowly in heavy downpours, so lean toward the steeper end of what works.
Permits
Attached lean-to additions and porch roofs often require a permit in Georgia jurisdictions; detached sheds may or may not. Check with your local building department. For flashing details, see roof flashing explained and roofing permits in Georgia.