Why Does Green Algae Keep Coming Back on My Siding?

You cleaned your siding last year, and here it is green again — usually on the same north- and east-facing walls. It's frustrating, and it almost always comes down to how it was cleaned the first time.

What the green actually is

That film is algae, and sometimes mildew and mould mixed in. It's a living organism, not just dirt. It settles on the walls that stay damp and shaded longest — which in Durham's humid, lake-influenced climate means the north and east sides of most homes. It feeds on the surface and spreads from its own roots.

Why it keeps coming back

Here's the key: a pressure washer knocks the green off the surface so the wall looks clean, but it leaves the organism's roots behind and doesn't kill the spores. Within a season, those roots regrow and you're right back where you started. You didn't fail to clean it — the method just treated the symptom, not the cause.

Rinsing algae off is like mowing a weed. Until you kill the root, it grows right back.

What actually stops it

Soft washing uses a biodegradable cleaning solution that kills the algae, mould, and mildew at the root rather than blasting the surface. Because the organism is dead instead of just displaced, the siding stays clean far longer — typically a year or more, versus a few months for a pressure rinse. It's also the only safe method for vinyl, brick, stucco, and stone, which high pressure can crack or drive water behind.

• Kills the growth at the root, so it doesn't regrow next season
• Safe for vinyl, brick, stucco, and stone — no cracking or water intrusion
• Results last a year or more instead of a few months
• Treats the shaded north and east walls where algae always starts

If you're tired of cleaning the same green wall every year, the fix isn't cleaning it more often — it's cleaning it properly once. Send us a photo of the affected side and we'll tell you what it'll take.