Why Your Siding Turns Green in This Humidity

Green streaking on siding, especially on the side of the house that does not get much direct sun, is not a sign of a leak or anything wrong with the house itself. It is algae. It shows up on cream and light-colored siding all over Middle Georgia for the same reason it shows up on concrete and roofs: moisture sits on a surface longer than it should, day after day, week after week. The good news is that it is surface growth, and it can be cleaned.

Why the shady wall looks worse

Algae spores travel through the air and land on every side of a house equally. They only take hold where moisture lingers long enough for them to grow. A north-facing wall gets less direct sun, so dew, rain, and overspray dry more slowly there than on a wall that bakes all afternoon. Add mature trees, a gutter that spills down the siding in a heavy storm, or a sprinkler head that clips the wall on every cycle, and that one section of the house stays damp far more often than the rest. That is why the streaks concentrate in one spot instead of spreading evenly.

Pressure washing versus soft washing

Siding, and vinyl siding in particular, is not built for the pressure that works fine on a concrete driveway. Blasting it at that level can push water up behind the panels, open seams, or crack older boards, and it still does not deal with the growth at its root. Soft washing handles both problems. A cleaning solution made for algae and mold goes on at low pressure, gets time to work, and is rinsed off gently. Because it kills the growth instead of just knocking the visible layer loose, a wall cleaned this way tends to stay clean longer than one that was only rinsed hard.

The photo with this article shows the problem on cream siding, streaked green from the top down. The crew's after photo of that wall shows it washed back to clean cream.

Gutters are part of the story

A clogged gutter does not only overflow in a storm. It channels water straight down the face of the siding every time it rains, which keeps that section wet long after the rest of the house has dried. Leaves and pine straw collect quickly under the tree cover common in Warner Robins yards, and a gutter ignored for a season is one of the more overlooked reasons a single stretch of wall stains faster than the rest. Cleaning the gutters is often as much a part of fixing recurring green streaks as washing the siding itself.

• Trees or dense shrubs shading a wall for most of the day
• A gutter that overflows or drips onto the siding below it
• A sprinkler head that hits the house instead of the lawn
• Plantings crowded against the foundation, blocking airflow along the wall
• A north or east wall that gets little afternoon sun

Concrete has its own version of this

Driveways and walks go through the same cycle. Concrete is porous, so algae and mildew get into the surface and the dark staining that follows is not plain dirt. A garden hose moves the top layer around and leaves the rest. Pressure is the right tool on concrete, but the surface should still come out uniform from edge to edge, without lighter stripes where the wand lingered or streaks where dirty rinse water ran back across a clean section. The crew's before-and-after photos of a heavily stained driveway show what a proper pass does: dark, blotchy concrete on one side, one even color on the other.

Keeping it from creeping back

Trim shrubs and low limbs back off the siding so air can move across the wall and help it dry between rains. Turn a sprinkler head that has been hitting the house. Keep the gutters clear. Then wash the shadier walls on a regular schedule, more often where the shade is heavy, so algae never gets the head start it needs to show up as visible streaks. Moisture that sits against siding long enough to grow algae is the same moisture that works into seams, trim, and fascia over time, so fixing the source protects the house, not just its looks.

What the crew washes

A.P. Lawncare & Pressure Washing LLC washes house exteriors, patios, driveways, and decks, and cleans gutters, for homes and commercial properties in Warner Robins and Houston County. One homeowner hired the crew to clear a backyard, clear a roof, take down an old gazebo, and wash the house and patio in one go. If a wall on your house has gone green, call (478) 334-1049 and describe which side it is on. That alone tells a lot.