Black streaks that look like dirt but never rinse away with rain — on shingles and in the valleys of barrel tile. That's algae, and it's the #1 thing stealing curb appeal on Clay County roofs.
Black streaks on shingles, dark patches in tile valleys, and gradual darkening of the whole roof plane. It looks like dirt or soot, but rain won't touch it.
The streaks are Gloeocapsa magma, an airborne algae that feeds on the limestone filler in shingles. Northeast Florida's humidity lets it spread roof to roof — and it gets worse every season it sits.
Most Clay County homes run $375–$1,200, priced at $0.25–$0.75/sq ft by size, pitch, material, and growth severity. Tile and steep roofs assessed on site. Text photos for a fast ballpark.
