Algae Streaks on Florida Roofs: Dirt, Damage, or Both?

Black streaks on a Tampa Bay roof are almost always blue-green algae that lives in humidity and feeds on limestone filler in asphalt shingles. North-facing and shaded slopes get it first. Oaks overhead make it worse.

It is ugly. It is not automatically a failed roof. A 8-year architectural shingle with algae can be cleaned. A 18-year shingle with algae is often also at the end of its granule life — cleaning it just shows you the bald spots.

Soft wash (low pressure, right chemistry) is the method. Pressure washing drives water under tabs and strips granules. If someone wants to “blast the roof,” don’t let them.

Copper or zinc strips near the ridge can slow regrowth. They are not a miracle. Algae-resistant shingles (copper-infused granules) are worth specifying on a new roof in this climate.

If you are deciding between a wash and a replacement, look at age, bald spots, curling, and the back slope. We will fly it and tell you which conversation to have.