How to Get Rid of Black Streaks on Your Roof (Safely)
Those dark streaks running down your roof aren’t dirt or age — they’re algae. Here’s what causes them and the safe way to remove them.
What the black streaks actually are
The streaks are a hardy blue-green algae (Gloeocapsa magma) that feeds on the limestone filler in asphalt shingles. It thrives in humid climates like North Texas and spreads fastest on shaded, north-facing roof slopes that stay damp.
Why you should never pressure wash a roof
High pressure strips the protective granules off shingles, can crack them, and may force water underneath — leading to leaks and a shortened roof life. It might look clean for a moment, but it causes damage that costs far more than the cleaning.
The safe fix: soft washing
Soft washing applies a low-pressure cleaning solution that kills the algae at the root, then gently rinses. Because it treats the organism rather than just blasting the surface, the streaks don’t come right back the way they do after a pressure rinse.
- No granule loss or cracked shingles
- Kills algae so results last longer
- Safe for the roof, gutters, and landscaping below
If black streaks are showing up on your roof, request a free quote for a soft wash — it’s the method roofing manufacturers recommend.