If you've noticed dark streaks running down your Houston roof, you're not alone — and it's not just dirt. Those stains are a living organism, and left alone they shorten the life of your roof. Here's what's really going on.
The black streaks are a blue-green algae called Gloeocapsa magma. It feeds on the limestone filler used in asphalt shingles, and it spreads via airborne spores — which is why you'll often see it appear on a neighbor's roof not long after yours. Houston's heat, humidity, and frequent rain make our region one of the worst in the country for it.
Notice the streaks are worse on the north-facing slope? That side gets the least sun, so it stays damp longest — perfect conditions for algae. Overhanging trees and shade make it worse, which is common in neighborhoods like The Woodlands and Spring.
As algae spreads it:
It's tempting to blast it off, but high pressure strips the very granules you're trying to protect and will void your shingle warranty. The shingle manufacturers and the ARMA recommend only one method: soft washing.
Our roof cleaning uses low pressure plus professional treatments that kill the algae at the root, not just on the surface. The streaks lift away, the growth stops returning for far longer than a rinse, and your shingles are never touched by damaging force. In Houston's climate we recommend a gentle clean every two to three years to keep algae from taking hold again.
While we're up there, it's the perfect time to soft wash the rest of your exterior too. Request a free quote and we'll get your roof looking new again — safely.
Want those streaks gone without risking your shingles? Our soft-wash roof cleaning is safe and warranty-friendly.