How flat roofs leak

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Flat and low-slope roofs in the valley show up on porch additions, mid-century sections of older Boise houses, and the commercial buildings along the corridors. The failures differ from pitched roofs: ponding water, seam openings in the membrane, and flashing at the edges where the flat meets a wall.

How flat roofs fail

Ponding is the big one, water that sits on the surface past the point it should have drained. Membrane seams open with temperature cycling, and the valley's big day-night swings work them loose over years. Penetrations (vents, skylights, HVAC curbs) leak at the flashing before the field membrane fails.

Patch it or replace it

A flat roof with isolated damage at seams or flashing can be patched correctly. A roof that has blisters across the field or ponding that has cooked the membrane usually gets the recover-or-replace conversation, a new membrane over the old where code allows, or tear-off where it does not. The roofer should tell you which situation you are actually in, not which one sells more material.

What to describe in the request

Where the flat section is, what the leak looks like, and roughly how the building sits. Say whether it is a home or a commercial building in the request, and which section of roof is the flat one.