The Black Streaks Aren't Dirt — They're Alive
Almost every South Florida home has them eventually. Dark vertical streaks running down the north or east-facing slope of the roof. Patches of green-black growth where the tile or shingle is shaded by a tree. A general dingy appearance even after recent rain. Most homeowners assume it's dirt that will eventually rinse off. It won't — because it isn't dirt.
What's actually growing on your roof is a hardy algae called Gloeocapsa magma, plus its frequent companion mildew and lichen. These organisms feed on the limestone filler in shingles and on the porous calcium content of cement and clay tile. They love South Florida's daily humidity. Once they take hold, they spread rapidly, especially on the sides of the roof that get less direct sun. Left alone, they shorten your roof's lifespan, void some shingle warranties, and make even a well-maintained home look neglected from the curb.
The fix is a properly applied roof soft-wash. We never use high pressure on a roof — that approach cracks tile, blows granules off shingles, and forces water under flashing. Instead, we apply a measured cleaning chemistry that kills the algae at the cellular level, dwells for the right amount of time, and rinses cleanly without ever requiring force. The roof comes back to its original color, the algae dies all the way to the spore, and the result lasts 3-5 years on most South Florida roofs.
Why Soft-Wash Is the Only Safe Method
- It's the method recommended by every major shingle manufacturer (GAF, CertainTeed, Owens Corning)
- Won't crack cement, concrete, or clay tile
- Won't dislodge ridge cap, valley flashing, or pipe boot seals
- Won't shorten roof lifespan by removing protective granules
- Kills algae at the cellular level — not just relocating spores
- Results last 3-5 years instead of weeks
Our Roof Cleaning Process
Every roof job follows a careful sequence. We start with a perimeter walk to assess fragile landscaping and identify weak spots on the roof — cracked tiles, missing pieces, soft underlayment, or compromised flashing. Anything that looks like it needs repair, we document and discuss with you before starting. Then we pre-rinse all landscaping and sod near the drip line of the roof, since runoff during the wash will carry chemistry off the roof and onto whatever's below.
Next, we apply soft-wash chemistry from the eaves up using low-pressure injection. Working bottom-up keeps streak patterns from forming as the solution flows down a wet surface. We let the solution dwell for the appropriate time — long enough to kill the colony, not so long that it dries on the surface — and then rinse with clean water at low pressure. The gutters get flushed at the same time so dead algae doesn't accumulate inside them. Final step: a clean-water flush of the landscaping, and a video walkthrough of before-and-after with you.
Tile vs Shingle vs Metal
The technique varies slightly by surface. Cement and clay tile (the most common in South Florida) tolerate slightly higher chemistry concentrations and a longer dwell. Asphalt shingle roofs need a more carefully calibrated mix because over-application can shorten shingle life. Metal roofs (rare but increasing) get the gentlest treatment of all. Whatever you have, it gets the right approach — we don't use a single recipe for every roof.
What We Do When We Find Damage
Every now and then, we find broken tile, missing flashing, or a compromised pipe boot during a roof cleaning. When we do, we document it and bring it to your attention immediately — sometimes with photos or video taken from the roof itself, since most homeowners can't see the damage from the ground. We don't do roofing repair ourselves, but we maintain relationships with trusted South Florida roofers and can coordinate the fix so you don't have to find someone independently. Several of our reviews mention this exact scenario, where we caught a tile issue and helped get it repaired during the same week as the cleaning.
Frequently Asked Questions
The dark streaks are caused by Gloeocapsa magma, a hardy algae that thrives in South Florida humidity. It feeds on the limestone filler in shingles and the porous surface of cement tile. Once established, it spreads quickly — especially on shaded sides — and pressure washing alone won't kill it.
Yes — high pressure can crack tiles, dislodge ridge caps, blow granules off shingles, and force water under flashing. We never use high pressure on a roof. Soft-wash is the only safe method recommended by every major shingle manufacturer.
Because soft-washing kills the algae at the cellular level, results typically last 3-5 years on most South Florida roofs. Coastal homes and homes with heavy tree cover may see new growth sooner.
Yes. Tile tolerates slightly higher concentrations and longer dwell. Shingle needs a more carefully calibrated mix. Either way, both are soft-wash — never pressure-blasted.
We document it and bring it to your attention. We don't do tile repair ourselves, but we maintain relationships with trusted South Florida roofers and can coordinate the repair.
A typical single-story 2,000-3,000 sq ft home takes 2-3 hours including setup, application, dwell time, rinse, and gutter flush.