How long does a flat roof last?

Why the ranges are so wide

Because they assume things that are often not true. Every published service life assumes correct installation, adequate drainage and reasonable maintenance. Remove any one and the number stops meaning much.

The commonest reason a flat roof underperforms is not the membrane. It is water that never leaves — because the fall was wrong from the start, because the structure has deflected, or because an outlet has been blocked for two years.

What shortens a flat roof

Ponding water, first and by a distance. Then foot traffic, particularly in cold weather and particularly where equipment needs regular access without walkway pads. Then penetrations added later by other trades and not properly detailed.

And heat, which is where the material choice does matter: a black EPDM roof on a large unshaded deck works harder than a reflective surface would in the same position.

What tells you where yours is

Seams lifting or separating. Terminations pulling away at parapets and walls. Cracking or crazing across the field on an older membrane. Ponding that has become permanent. And, from inside, staining that appears in a different place each time it rains.

A roof at fifteen years with clear drains and sound seams may have plenty left. A roof at ten with permanent ponding and failing terminations may not. Age on its own is a weak signal — which is why we photograph condition by area rather than giving one verdict for the whole roof.