North-side algae removed from this home’s siding.

The project

A common siding problem with a satisfying result.

The heaviest buildup was on the north side of the home, where gray-green spotting had spread across the light-colored siding and around a window. We cleaned the affected exterior surfaces with a siding-appropriate house-washing process and rinsed away the loosened organic growth.

The siding came out bright and clean, and the home’s original color looks much more consistent from one section to the next.

Why the north side?

Less sunlight means siding stays damp longer.

The north side of a house usually receives less direct sunlight than the other sides. After rain, morning dew, or humid weather, that shaded siding can take longer to dry. The combination of shade, lingering moisture, and airborne organic material creates favorable conditions for algae and similar growth.

Trees, nearby structures, and limited airflow can make the problem more noticeable. Cleaning the buildup when it appears helps the siding look cared for without waiting for the discoloration to spread.