Those dark streaks are not dirt. They are a bacteria called Gloeocapsa magma that feeds on the limestone filler inside asphalt shingles, and it spreads a little further every year it stays up there.
You will usually see the streaks show up first on the north facing slope of the roof, because that side stays damp the longest in Central Kentucky humidity. Left alone, the bacteria eats at the shingles, holds moisture against the roof, and shortens its life.
The fix is a zero pressure roof cleaning. We apply a cleaning solution that kills the bacteria and the streaks fade out over the following weeks as rain rinses the dead growth away. Nobody should ever put a pressure washer on your shingles. It blasts away the protective granules and can void your warranty.
Most roofs in the Lexington area run $599 to $1,299 to clean and stay clean for three to five years. If you are seeing the first few streaks now, sooner is cheaper than later.
Answer last updated August 12, 2026. Prices on this page come straight from our current price list, so what you read here is what we quote.
More detail, photos, and what's included: Roof Cleaning in Central Kentucky.
