Green algae or mildew on siding — New York, New York
Green or black streaks on vinyl, wood, or fiber-cement siding are usually algae (Gloeocapsa magma) or mildew colonies fed by moisture and shade. Left alone they trap moisture against the surface, accelerating rot in wood and degrading paint. A professional pressure washing ($200–$500 for an average home exterior) removes these growths in 2–3 hours using a soft-wash technique — low pressure (under 1,500 PSI) with a sodium hypochlorite or oxygen bleach solution that kills spores without damaging siding. Standard high-pressure washing can force water behind siding laps on vinyl and splinter softwood grain, so soft-wash is the industry standard for building exteriors.
Who to call
For this problem in New York, call a: Schoonmaker
Vind een Schoonmaker in New YorkSymptoms to look for
- Green, black, or dark streaks on siding that don't wash off with a garden hose
- Siding feels slimy or slippery to the touch in shaded areas
- Discoloration worsens on north-facing walls or under trees
- Musty outdoor smell near the house foundation
Spoeddienst in New York
Emergency home services in New York City are available 24/7 but come at premium rates — expect $150–$300+ per hour for after-hours plumbing or electrical emergencies. Response times average 45–90 minutes in Manhattan, longer in outer boroughs. Always verify the provider's NYC license before letting them in.