Those black streaks are not dirt. Here is what actually causes them, how often a roof in this climate needs treatment, and why pressure alone makes the problem worse.
If you live in Broward or Palm Beach County, you have seen the dark streaks that run down tile and shingle roofs. Most people assume it is dirt or mildew stains that will rinse off. It usually is not.
What the black streaks actually are
The staining is usually algae growth. Our combination of heat, humidity and frequent rain gives it close to ideal conditions year round, which is why roofs here discolor faster than roofs in drier states. Because it is a living organism rather than surface grime, rinsing it away does not stop it. Whatever remains in the pores of the tile simply regrows.
Why high pressure is the wrong tool
This is the part that costs homeowners money. Aiming a high-pressure tip at a roof can strip the granules off asphalt shingles, force water under tile, and crack older or brittle material. You get a roof that looks clean for a few weeks and ages faster than it should.
The correct approach on a roof is a low-pressure treatment that kills the growth at the root, then a gentle rinse. We save true high pressure for surfaces built to take it, like concrete driveways and paver walkways.
A realistic schedule for this climate
- Roofs: every 18 to 24 months for most properties, sooner if you are near the water or under heavy tree cover
- Driveways and walkways: once a year, or twice where cars drip oil
- Pool decks and patios: once a year, mainly for slip safety
- Building facades: every 1 to 2 years depending on exposure
Properties close to the coast tend to need attention sooner. Salt in the air holds moisture against the surface, and shaded north-facing slopes stay damp longer, so they green up first. If you are unsure, we will look at it and tell you honestly whether it can wait another season.
