When most homeowners think about maintenance, the roof rarely tops the list. Out of sight often means out of mind—until a leak appears or shingles start falling apart. As someone who cleans roofs for a living, I can tell you this with confidence: a dirty roof isn’t just a cosmetic issue—it’s a structural one.
Roof cleaning isn’t about making your house look pretty (though that’s a nice bonus). It’s about preserving materials, preventing damage, and extending the life of one of the most expensive components of your home.
Let’s break down why roof cleaning actually matters.
What’s Really Growing on Your Roof?
Those dark streaks or green patches you see aren’t dirt. They’re living organisms.
The most common culprits include:
- Algae (Gloeocapsa magma) – Causes black streaks and feeds on limestone fillers in shingles
- Moss – Thick, sponge-like growth that holds moisture against the roof
- Lichen – A stubborn combination of algae and fungus that roots into shingle surfaces
These organisms thrive in damp, shaded environments—exactly what roofs in the Pacific Northwest and similar climates provide.
The problem isn’t that they exist. The problem is what they do while they’re there.