Green Algae on Your Siding: Why Atlanta Homes Get It and How to Remove It Safely
What that green film actually is, why it loves metro Atlanta houses, when cleaning it yourself is fine, why a pressure washer makes it worse, and what professional removal costs.
The short answer
The green film creeping up your siding is algae, usually mixed with a little mildew, and in metro Atlanta it is close to inevitable: our humidity, shade trees, and pollen film give it everything it needs. A small patch on a reachable wall is a fine DIY job with a garden sprayer and a soft brush. A whole green wall, a two-story house, or growth that keeps coming back is a job for a low-pressure soft wash, which kills the growth at the root instead of smearing the surface layer around. A full house soft wash in metro Atlanta typically runs 300 to 600 dollars, and the one thing you should never do is aim a pressure washer at your siding, because high pressure damages the panels and the algae comes right back anyway.
Why metro Atlanta houses grow algae so fast
Algae needs three things: moisture, shade, and food. Metro Atlanta supplies all three in bulk. Summer humidity keeps siding damp long after the morning burns off, and the same tree cover that saves your cooling bill keeps whole walls in shade. The spring pollen dump leaves a film on every surface that algae happily feeds on, along with everyday dust and organic debris. That is why the growth almost always shows up first on the north side of the house and on any wall that sits behind trees, while the sunny south side stays clean. If your neighbor has it, spores are drifting to your walls too, and gutters that overflow or drip down the siding draw green stripes exactly where the water runs.
What it costs you to ignore it
- It spreads, and it holds moisture against the house. A light haze becomes a green wall in a season or two, and that damp layer feeds mildew and slowly works on paint, trim, and caulk lines.
- It stains. The longer it sits and bakes through Georgia summers, the deeper the discoloration sets into vinyl texture and painted surfaces, and the harder it is to get a uniform clean.
- It reads as neglect. A green-streaked house drags down curb appeal, invites HOA letters, and is one of the first things buyers notice from the street.
- It makes surfaces slick. The same growth on a shaded walkway, steps, or deck nearby is genuinely slippery when wet.
DIY algae removal: when it makes sense and how to do it right
If the growth is a light patch on a ground-level wall, cleaning it yourself is reasonable. A few rules keep it safe and effective:
- Use a house-wash solution and a soft brush or garden sprayer, not a stiff brush and not raw strength cleaner. Gentle chemistry does the work; scrubbing hard just spreads the growth around.
- Protect your plants. Wet down the grass and beds under the wall before you start and rinse them again after. Cleaning solutions and landscaping do not mix.
- Work top to bottom and rinse with a garden hose, letting the solution sit for several minutes first so it actually kills the growth instead of just wiping the surface.
- Stay off ladders with a sprayer in your hand. If you cannot reach it comfortably from the ground, that is the line where DIY stops making sense.
Why a pressure washer is the wrong answer
It is tempting, because high pressure visibly strips the green off. Two problems. First, pressure damages siding: it can force water behind vinyl panels where it sits against the sheathing, strip the finish off painted surfaces, and etch soft materials. Second, it does not actually kill anything. Blasting removes the surface layer while the roots stay in the texture of the siding, so the wall greens back up in months. This is the whole reason the industry moved to soft washing instead of pressure washing for houses: low pressure, the right cleaning mix, and dwell time kill the growth itself, which is why the results last one to three years instead of one season.
"The houses we get called to fix are almost never the ones nobody cleaned. They are the ones somebody pressure washed a year ago, and the algae came straight back."
How a professional soft wash removes algae
- Inspect the siding and pick the right mix. Vinyl, HardiePlank, brick, and painted wood each get the solution matched to the surface and the growth.
- Protect the landscaping. We pre-wet plants and beds around the house and keep them rinsed the whole time.
- Apply at low pressure. The mix goes on at roughly garden-hose pressure, reaching into the siding texture where the growth actually lives.
- Let it dwell. The solution needs minutes on the wall to kill algae and mildew at the root. This step is the difference between clean for years and clean for a season.
- Rinse and verify. Top-to-bottom gentle rinse, re-treat any stubborn spots, and a final fresh-water rinse for the plants.
While we are on the walls we also flag anything worth knowing about, like failing caulk, gutter overflow lines, or the black streaks on shingles that mean the roof has the same problem.
What algae removal costs in metro Atlanta
| Job | Typical range |
|---|---|
| House soft wash (full exterior siding) | $300 to $600 |
| Full exterior package (house + driveway + walkways) | $400 to $800 |
| Roof soft wash (black algae streaks on shingles) | $400 to $900 |
| Spot treatment of one wall | Ask for a quote |
Most of a job's cost is setup and travel, so bundling the driveway, windows, or gutters into the same visit is cheaper than booking each on its own. Full numbers in our 2026 pricing guide.
Algae removal in your city
We soft wash houses across Marietta, East Cobb, Roswell, Alpharetta, Buckhead, and the rest of metro Atlanta. See the house washing page for the full service, or slot it into your yearly exterior maintenance cycle. Text us a couple of photos of the wall and we will send a free, honest quote.
Common questions
What is the green stuff on my siding? Algae, usually with some mildew mixed in. It feeds on moisture and the pollen film, which is why it starts on shaded, north-facing walls.
Does it damage the siding? Over time, yes. It holds moisture against the house, feeds mildew, and stains. Caught early it washes off completely.
Can I just pressure wash it? Please do not. High pressure can force water behind the panels and only strips the surface growth, which comes back in months. A soft wash kills it at the root.
How much does removal cost? A full house soft wash typically runs 300 to 600 dollars in metro Atlanta, less per-service when bundled with other exterior work.
How long does it stay clean? One to three years for most homes, longer on sunny exposures, slightly less under heavy shade.