Why are my roof shingles turning black?
Short answer. The most common reason is algae: dark streaks running down the slope, especially on north-facing and shaded roofs in humid Georgia. But shingles also look black where granules have worn or been knocked off and bare asphalt shows, where a roof stays damp in shade, or where soot or debris collects, and each cause calls for a different response.
Tell the causes apart
- Algae streaks. Long vertical stripes running downslope, often starting below the ridge and heavier on north and shaded sides. The shingle surface is intact under the stain. Mostly cosmetic.
- Granule loss. Black patches where the colored granules are gone and the asphalt shows. Look for granules piling in gutters and at downspout outlets. A sign of aging, or of hail if the spots are random and roughly circular.
- Whole-roof darkening. Shingles that look darker overall when wet or in shade, or an older roof whose granules have weathered. Often normal aging.
- Moss and lichen. Green, gray or black growth with texture you can see. Holds moisture and can lift shingle edges.
- Soot or debris. Dark areas near chimneys or under trees, where pollen and organic matter collect.
What to do about each
Algae can be cleaned gently with a solution made for roofs, applied at low pressure, never pressure washed, which strips granules. Zinc or copper strips near the ridge slow regrowth. Granule loss cannot be repaired: it means the shingle is wearing or was damaged, and widespread loss points toward replacement or, after a storm, an insurance inspection. Moss needs careful removal and more sunlight.
When it is more than cosmetic
Random black spots that feel soft or show cracked mat after a hailstorm are damage, not stains, and may be covered by insurance. Photograph them and have the roof inspected before cleaning anything.
Details in black streaks and algae on roofs, moss and lichen on roofs, and signs you need a new roof.