What Causes the Black Streaks on Your Roof?
If your roof has dark streaks running down from the ridge, you’re not looking at dirt, soot, or simple aging. You’re looking at a living organism — and how you deal with it determines whether your roof gets clean safely or gets damaged.
It’s algae, not dirt
The black streaks are a type of cyanobacteria, Gloeocapsa magma, that feeds on the limestone filler in asphalt shingles. It spreads via spores carried on the wind, which is why one streaky roof in a neighborhood often means several. It thrives in humid climates and on shaded, slow-to-dry roof sections — exactly the conditions common around Springfield, TN.
Why it matters beyond looks
Left alone, the growth holds moisture against the shingles and gradually breaks down the granules that protect them, which can shorten a roof’s life. So it’s not purely cosmetic — though the curb-appeal hit is real too, especially if you’re selling.
Never pressure wash a roof
This is the critical point: a roof should never be cleaned with high pressure. The force tears the protective granules off asphalt shingles and can force water under them, doing far more damage than the algae. The correct method is a soft wash — low pressure with a cleaning solution that kills the organism so it doesn’t simply grow back.
If your roof is streaking, Springfield Pressure Washing Pros can soft wash it safely. Call (629) 266-2744 for a free, no-obligation quote.
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