black streaks on house and roof · Columbus, GA

black streaks on house and roof in Columbus

In Columbus, this comes up on historic-district houses, mid-rise buildings, hotels, and industrial sites. Uptown brick holds a green film. Industrial eaves go black. Drives in the older blocks are stained through. 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.

Venues, churches, and high gutters stay on the calendar when house washing slows.

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.

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