Why Is One Side of My House Green? (And How to Get Rid of It)

By Kenny Monks, owner of Rooted Exterior Solutions · October 2026

Short answer: it's algae and mildew, and it grows on the side of your house that stays shady and damp the longest, usually the north side or the side under trees. That side gets less sun, so it dries slowly after rain and dew. In the CSRA's humid climate, that's all algae needs. A soft wash kills it at the root. Pressure washing just blasts off what you can see and can damage the siding.

Why only one side?

Sun dries siding. Here in the CSRA, the north side of a house gets the least direct sun. Add a big oak, a row of pines or a close neighbor, and that side can stay damp for hours after every rain and every morning dew. The sunny side dries fast and stays clean. That's why you'll see a house that looks fine from the street but is green around the back corner.

Around Augusta we get about 45 inches of rain a year and humid summers, so a shaded wall can turn green within a year or two of being cleaned. I see it on brand-new homes in Grovetown and Evans just as much as older ones in Summerville and downtown Aiken. I've washed around 4,000 homes across the CSRA, and the green side is almost always the one that faces north or sits under trees.

Is it hurting my house?

Mostly it's cosmetic at first, but it isn't harmless:

• It holds moisture against siding, trim and caulk.

• On painted wood, it speeds up peeling and rot.

• It spreads to gutters, soffits, the porch ceiling and the roof.

• Many HOAs will send a notice about mildew on siding.

Why not just pressure wash it?

High pressure can crack vinyl siding, force water behind the panels, strip paint and damage older wood and brick. It also only removes what's on the surface. The algae roots stay put, so the green comes back fast.

A soft wash uses a cleaning solution at low pressure to kill the algae and mildew, then rinses it away. It's gentler on the house and lasts longer. I wrote about the difference in more detail in soft washing vs. pressure washing.

How do I keep it from coming back?

• Let in more sun. Trim back branches that hang over or touch the house.

• Fix water sources. Clogged gutters that overflow, sprinklers that hit the siding and downspouts that dump next to the wall all keep the area wet.

• Clean it before it builds up. Heavy growth is harder to remove than a light film. Many CSRA homes need a house wash about once a year.

Frequently asked questions

Is it mold?

Usually it's algae, with some mildew. Either way, a soft wash kills both.

Will bleach from the store fix it?

It can lighten it, but mixing, applying and rinsing wrong can hurt plants, leave streaks or stain siding. Getting the whole house evenly is the hard part.

Is soft washing safe for plants and pets?

Yes, when it's done right. I pre-wet and rinse plants, and pets should stay inside until everything is rinsed.

How long does a house wash take?

Most homes take a few hours.

What does a house wash cost?

Most homes run about $300 to $500, set by size and difficulty. Every quote is free.

Kenny and the team at Rooted soft wash houses in every neighborhood in the CSRA. See house washing in North Augusta, Aiken or Augusta, or call or text Kenny at 803-220-1722 for a free quote.