Maintenance
Black Streaks, Algae and Moss on Roofs
Updated · Sabine Crest editorial
Algae
Usually cosmetic but shading and moisture help it spread. Zinc or copper strips near the ridge slow regrowth.
Moss
Grows on shaded, damp roofs under pines and oaks. It lifts shingle edges and traps moisture.
Cleaning safely
Low-pressure treatment only. Pressure washing strips granules and can void warranties. Trim trees to add sun.
Safe cleaning
Use a low-pressure wash with a roof-safe cleaner; pressure washing strips granules and shortens shingle life. Zinc or copper strips near the ridge slow regrowth, and algae-resistant shingles help on replacement.
Why it's common in Southeast Texas
High humidity, heavy rain and shade from pines and oaks keep roof surfaces damp for long periods, which is ideal for algae (the black streaks) and moss on north-facing slopes.
Black Streaks, Algae and Moss on Roofs: follow-up questions
Do black streaks damage my roof?
The common black algae is mostly cosmetic, though it can hold heat. Moss is more harmful because it traps moisture.
Can I pressure wash my roof?
It's not recommended. High pressure removes protective granules.
Does algae void my shingle warranty?
Usually not, though cleaning methods that damage shingles can. Check the manufacturer's guidance.
Are algae-resistant shingles worth it?
They contain copper granules that slow growth and are a sensible choice in humid, shaded areas.
Every home differs; editorial standards.