What roof pitch do I need?

Start with the material

• Asphalt shingles: 2/12 minimum, with double underlayment up to 4/12. At 4/12 and above, standard installation applies.
• Exposed fastener metal panels: 3/12 minimum without lap sealant; many installers prefer a bit more on a house.
• Standing seam metal: code allows very low slopes, but each panel maker sets its own minimum, and snap-lock profiles often need more slope than mechanically seamed ones.
• Membranes (TPO, EPDM, modified bitumen): for nearly flat porches, generally a quarter inch per foot so water still drains.

Planning a porch, shed or addition

The usual squeeze is height. A porch or sunroom that ties into the wall below second-floor windows needs room for flashing to run up the wall several inches above the roof surface, and still clear the window sill. Designers often land at 3/12 or 4/12 for that reason. If the addition has its own gable, matching the main roof's pitch makes valleys meet cleanly and looks intentional. Any structural addition in Georgia will need a permit and framing that the building department approves; see roofing permits in Georgia.

How much pitch does a metal roof need?

For the ribbed, screw-down panels common on Georgia barns, porches and some homes, plan on 3/12 or more. For a low porch where you want metal, standing seam is the safer route, built to the manufacturer's stated minimum. More in metal roofing in Georgia.

Think about the rain

Georgia storms can drop an inch or more of rain in an hour. A big, shallow roof collects a lot of water and moves it slowly, so the valleys, gutters and the joint where a low roof meets a wall carry most of the risk. When in doubt, a little more pitch is cheap insurance.