If you look at roofs in your neighborhood, you’ll likely notice unsightly black streaks on many of them. These streaks are actually a type of algae called Gloeocapsa magma, which feeds on the limestone filler in asphalt shingles. While it looks terrible, the bigger problem is that it’s slowly damaging the roof. The natural reaction is to want to blast it off with a pressure washer, but doing so is a costly mistake.
High-pressure washing should never be used on an asphalt shingle roof. The intense blast of water easily dislodges the protective granules that coat the shingles. These granules are essential for reflecting UV rays and protecting the asphalt underneath. Removing them significantly shortens the lifespan of your roof and can instantly void your manufacturer’s warranty. It’s an aggressive approach that solves a cosmetic problem by creating a structural one.
The correct, professional solution is soft washing. This method uses specialized, low-pressure equipment — often no more pressure than a standard garden hose — to apply a custom-blended cleaning solution. The cleaning agents do the hard work, killing the algae, mold, and lichen down to their roots. The solution is then gently rinsed away, leaving the roof looking brand new without any damage to the shingles.
Soft washing provides a longer-lasting clean because it kills the organisms at the biological level rather than just washing away visible surface growth. High-pressure washing simply displaces the contamination temporarily — the surviving spores regrow rapidly because the root structure remains intact. A properly applied soft wash solution can keep your roof clean for three to five years, making it both the safest and the most cost-effective approach for roof maintenance.