Mildew on Siding: Why North and Shaded Walls Turn Green and How to Slow It
Green, gray or black film on north-facing and shaded siding is usually mildew or algae growing on dirt that never fully dries. It is common around Matthews and Mint Hill, where tall trees shade many houses and summers are humid.
Why the North Side
A north wall gets little direct sun, so dew and rain dry slowly. Add shade from trees, shrubs against the wall, and a film of pollen and dust for food, and growth starts within a season. The EPA notes that controlling moisture is the key to controlling mold and mildew.
Is It Harming the House?
On vinyl and fiber cement, mostly it is cosmetic, but it holds moisture against the surface. On painted wood and hardboard, a wall that stays damp is a wall where paint peels and wood rots sooner. Black streaks under gutters and around window corners point to water running down the wall.
Cleaning It
- Soft wash. A cleaning solution with a mildewcide, applied at low pressure and allowed to work, then rinsed. Scrub stubborn spots with a soft brush.
- Protect plants. Wet plants before and rinse after.
- Do not blast it. High pressure can damage siding and force water behind it.
Painting over mildew without killing and washing it off lets it grow through the new paint.
Slowing It Down
- Trim branches to let in sun and air.
- Keep shrubs a foot or more off the siding.
- Clean gutters and fix overflows.
- Wash the house yearly, after spring pollen.
- When repainting, use an exterior paint with mildewcide in the film.
Frequently Asked Questions
Is mildew on siding the same as mold?
Mildew is a common name for surface mold growth. On siding it is usually mildew, algae, or both.
Will bleach alone kill mildew on siding?
It can lighten it, but it is harsh on plants and some surfaces. Purpose-made house wash cleaners with mildewcide work better.
How often should I wash a shaded house?
Once a year, sometimes twice for walls that stay damp.
Will paint stop mildew?
Paint with mildewcide slows regrowth, but shade and moisture will still let it come back eventually.
Green Siding?
We soft wash shaded walls as part of every exterior job, or on its own. See house washing or contact us.