You’ve seen them on roofs all over Atlanta: dark, streaky stains running down from the peak. Many homeowners assume it’s just dirt or water staining. The truth is a little more alarming — and worth understanding.
It’s Actually Living Algae
Those black streaks are a type of blue-green algae called Gloeocapsa magma. It thrives in warm, humid climates (hello, Georgia) and feeds on the limestone filler in asphalt shingles. As it spreads, it forms dark streaks that get worse year after year.
Why You Shouldn’t Ignore It
Algae isn’t just an eyesore. Left untreated, it:
- Shortens your roof’s lifespan by breaking down shingle material
- Raises cooling costs, since dark streaks absorb more heat
- Hurts curb appeal and resale value
- Spreads to neighboring shingles and can invite moss and lichen
The Wrong Way to Fix It
Whatever you do, don’t pressure wash your roof. High pressure tears the protective granules off asphalt shingles, drastically shortening their life and often voiding the manufacturer’s warranty. We’ve seen homeowners cause thousands of dollars in damage trying to DIY this.
The Right Way: Soft Washing
The roofing industry (ARMA) recommends a soft wash approach — no high pressure at all. We apply a specialized cleaning solution that kills the algae, moss, and lichen at the root, then gently rinse. The streaks disappear, and because the algae is killed rather than just rinsed, your roof stays clean far longer.
Done correctly, roof soft washing restores your shingles’ color and protects your warranty — no damage, no risk.
Protect Your Roof the Smart Way
If your roof is showing black streaks, the sooner you treat it, the more shingle life you’ll save. Get a free roof washing quote and let our team safely restore your roof to like-new condition.