black streaks on house and roof · Senoia, GA
black streaks on house and roof in Senoia
In Senoia, this comes up on downtown storefronts, cottages, and houses that face foot traffic. Sidewalks collect drink stains, pollen, and the general wear of a town people walk. North slopes and walls under pines show it first. If the street face is clean and the back is black, that is the shade, not a half-finished wash.
Holiday weeks are when a Senoia storefront and a cottage porch are looked at twice.
The organism most people are looking at on asphalt shingles is an algae that protects itself with a dark pigment. It runs with water and leaves the streak. On siding, mildew and algae make a similar dark film, especially where a sprinkler or a tree keeps the wall damp. Sodium hypochlorite kills it. A brush and a garden hose smear it.
Killing it does not change the conditions. If the wall stays shaded and wet, a new film will start. In this part of Georgia and east Alabama that is often visible again within a year or two on the worst elevation, and longer on a sunny wall. We will not sell an annual result as a ten-year result.
If the “streak” is actually granule loss, or a tar drip, or a rust run from a metal valley, bleach will not fix the look. We will say which one we think it is when we see a photo. A close photo of the streak beats a paragraph.
The full explanation, without the town attached, is the black streaks are a colony, not dirt article. The town does not change the chemistry. It changes the houses, the shade, and the clay.