Why does my porch roof keep leaking when the rest is fine?
Porch roofs, additions and carports often have a lower slope than the main roof, and many are covered with shingles. Shingles need enough slope to shed water. Below about a 2:12 pitch, water can sit on the shingles and work its way underneath, which leads to leaks. A flat roofing system or standing seam metal is usually a better choice for low-slope areas.
Roof pitch and shingles
Shingle manufacturers publish a minimum slope for their products, usually 2:12, with extra underlayment required near that limit. On a roof below the minimum slope, the shingles are outside the manufacturer’s specifications and the warranty may not apply.
On low-slope sections, the problem is usually the material that was chosen for the roof.
Better options for low-slope roofs
Flat roofing systems, such as modified bitumen or single-ply membrane, are designed for low-slope roofs and seal against water.
Standing seam metal also works well on many low-slope roofs and gives the area a clean, finished look.
Where the low-slope roof meets the main roof
The area where a low-slope section meets the main roof or a wall is a common place for leaks. The roofing and flashing at that transition have to be installed correctly to keep water out.
When a porch or addition leaks, this transition is one of the first places to check.
Repair or replace?
If the roofing on a low-slope section is in good condition, a repair may be enough. If the decking underneath is wet or damaged, the section will need to be replaced.
An inspection will show which option your roof needs.
Related Questions
Can more sealant fix the leak?
Sealant may stop a leak for a short time, but it does not fix shingles that are installed on too low a slope.
How much of the roof has to be replaced?
Usually only the low-slope section and the area where it meets the main roof.
Will a flat roof look different?
Yes. A flat roofing system looks different from shingles, and it is designed for low-slope areas.
How long does a flat roof last?
It depends on the type of system and how well it was installed. Edges, curbs and transitions are the most common places for problems.
