Why Low-Slope Porch and Addition Roofs Leak

The problem with low slope

Asphalt shingles depend on gravity. They're designed for roofs with enough pitch for water to run off quickly. Many porches, carports, sunrooms and older additions were built with a much flatter slope, and shingles or rolled roofing on those roofs let water sit, back up under laps and leak.

Common trouble spots

• Shingles installed below the slope the manufacturer allows.
• Rolled roofing that has cracked, blistered or lost its seal at laps.
• The joint where the porch roof meets the house wall.
• Ponding water from sagging framing.
• Gutters too small for the area, overflowing at the house corner.

What works on low slopes

Low-slope roofs need materials made for them, such as membrane roofing systems or properly detailed metal, and the roof-to-wall joint needs flashing that runs up behind the siding. Sometimes the better fix is to add slope by reframing the porch roof so it can take the same shingles as the house. See roof-to-wall flashing and metal roof options.

Check the framing

Years of leaks on a porch roof often rot the decking, rafters or the beam at the edge. Those have to be repaired before new roofing goes on. See rotted decking repair.

AGCS handles both the roofing and the framing — see roof repair and porch construction.

Frequently Asked Questions

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