How Long a Roof Lasts on the Coast

It damages it. Moss acts like a sponge sitting on the surface, so the shingle underneath stays saturated long after the rain stops. As the mat thickens it lifts the bottom edge of the course above, which lets wind-driven water travel sideways under the shingle. Lichen is worse because it bonds into the granule layer and pulls granules off when removed.

Sun and airflow dry a roof, and the north slope gets neither. It stays damp for most of the wet season, which is exactly the condition moss and lichen need. The south slope gets more UV and loses granules faster in a dry climate, but on the coast the shaded slope usually fails first. It is normal to see two very different roofs on one house.

Two-ply torch-on membrane on a flat or low-slope roof typically runs 20 to 25 years on the coast, sometimes longer when the detailing and drainage are right. The failure point is almost never the field of the membrane. It is the seams, the flashing at parapets and curbs, and the drains. A flat roof that ponds after every storm is telling you the drainage or the slope needs attention, not the membrane.

Sometimes. If the shingles still hold granule cover and the deck feels solid underfoot, clearing drainage, cleaning moss off the roof and repairing flashing can buy several more seasons. If granules are gone, edges are curling, or the deck flexes when you walk on it, you are delaying a replacement rather than avoiding one. Avoid pressure washing either way, since it strips granules and takes life off the roof.

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