If you've looked up at your roof lately and noticed dark vertical streaks running down the shingles, you're not imagining it — and it's not just "weathering." Those streaks are biological, and they're spreading.
What Those Streaks Actually Are
The dark stains on your roof are caused by Gloeocapsa Magma — a hardy cyanobacteria (commonly called blue-green algae) that feeds on the limestone filler used in modern asphalt shingles. It's not mold, it's not dirt, and it's not washed away by rain.
South Louisiana is one of the worst environments for it on the entire Gulf Coast. Long, humid summers + frequent rain + warm winters give the colony a 12-month growth window. By the time most homeowners notice the staining, the colony is already 18-36 months established.
Why You Can't Ignore It
- It eats your shingles. Gloeocapsa breaks down the limestone granules — the same granules that protect the asphalt from UV. As granules erode, shingle life shortens significantly.
- It traps moisture. The bacterial mat holds water against the shingle surface, accelerating freeze-thaw damage in winter and contributing to underlayment rot.
- It spreads to your siding. Spores wash down the roof and colonize gutters, fascia, and the top portions of siding. The black streaks you eventually see on your house often started on the roof.
- It costs you on resale. A streaked roof signals deferred maintenance to buyers and lenders. It's one of the cheapest things to fix and one of the highest-impact curb appeal issues.
Why Pressure Washing Makes It Worse
Asphalt shingles are not designed for high-pressure water. Putting 2,000-4,000 PSI against your roof does three things:
- Blasts the protective granules off the shingles, dramatically shortening roof life
- Forces water under the shingle laps and into the underlayment
- Voids most major shingle manufacturer warranties
It also doesn't kill the bacteria — it just rinses the visible surface. The colony regrows in 6-12 months.
Your shingle warranty
GAF, CertainTeed, Owens Corning, and most major manufacturers explicitly exclude pressure-washed roofs from warranty coverage. Check your roof's warranty paperwork before letting anyone put a wand to it.
The Method That Actually Works: Soft Wash
Soft wash is a low-pressure application (under 500 PSI — typically 100-200 PSI) of a sodium hypochlorite blend with surfactants. The chemistry does the work, not the pressure. It:
- Kills the bacteria at the root — not just the visible surface
- Preserves your warranty — within manufacturer specs for cleaning method
- Lasts 4-7 years on most Louisiana roofs vs 6-12 months for pressure washing
- Treats the gutters and downspouts as part of the rinse, killing spore reservoirs
What to Look For When Hiring
If you're getting quotes for roof cleaning, ask these three questions. If the answer to any is wrong, walk away:
- "Is this soft wash or pressure wash?" — answer must be soft wash for shingles
- "What's in the cleaning solution?" — answer should include sodium hypochlorite (the active ingredient that kills Gloeocapsa)
- "Do you protect landscaping and pre-rinse?" — yes; the sodium hypochlorite will brown grass and damage shrubs if not properly diluted and rinsed
Cypress Pro Wash uses soft wash exclusively for residential roofs in Ascension Parish. We tarp and pre-wet vegetation, apply the cleaning solution, let it dwell, then rinse. The black is gone before we leave the property.
How Soon Do You Need to Act?
Once you can see the staining from the street, the colony has been established for over a year. Every additional month of growth is more granule loss. We recommend treatment within a season of first noticing visible staining — and a preventive treatment every 4-6 years to keep it from coming back.