What the black streaks on your roof actually are
They are not dirt, soot, or 'weathering'. They are gloeocapsa magma, an algae that arrived in the south-east decades ago and thrives in Jacksonville's heat and humidity.
Modern asphalt shingles contain limestone filler. The algae feeds on it. The dark streaks are the organism's protective sheath, which it grows to survive UV exposure — which is also why the streaks always run downward, following how rainwater carries spores across the roof.
This matters for two reasons. First, it is alive, so it spreads and it comes back if you only remove the surface. Second, it is consuming part of your roof: heavily colonised roofs lose granules faster and run hotter, because the dark colonies absorb heat your shingles were designed to reflect.
Why nobody should pressure wash your roof
The Asphalt Roofing Manufacturers Association is explicit on this: shingles should be cleaned with a chemical solution and low-pressure rinse, not a pressure washer. Most shingle warranties are void if pressure washing has been used.
The reason is mechanical. The coloured granules on an asphalt shingle are the UV shield for the asphalt beneath. Strip them and the asphalt is exposed to Florida sun, becomes brittle, and the shingle fails years early. You will see the evidence in the gutters — a pressure-washed roof drops a gutter full of granules.
Tile and metal roofs are less fragile but bring their own problem: pressure drives water up under the tile laps or the metal panel seams, into the underlayment.
| Roof type | Correct method | Pressure | Risk if pressure washed |
|---|---|---|---|
| Asphalt shingle | Soft wash, chemical dwell, low rinse | Under 100 PSI | Granule loss, warranty void, early failure |
| Concrete / clay tile | Soft wash | Under 500 PSI | Cracked tiles, water under laps, underlayment damage |
| Metal / standing seam | Soft wash, neutral detergent | Under 500 PSI | Water forced through seams, coating damage |
| Flat / modified bitumen | Soft wash, careful rinse | Under 300 PSI | Seam separation, ponding damage |
Roof cleaning cost in Jacksonville
Roof cleaning is priced on roof area, pitch and access — not on the home's floor area. A steep roof needs more setup and more safety equipment, and that is the biggest single cost driver after size.
- Bundling a roof clean with a house wash on the same visit typically saves $75–$125
- Very heavy colonisation may need a second application, adding roughly 20%
- Solar panels on the roof add setup time and are cleaned separately
| Roof | Approx. area | Price range | Time |
|---|---|---|---|
| Single storey, low pitch | 1,500 sq ft | $399 – $549 | 3 hours |
| Single storey, steep pitch | 1,500 sq ft | $479 – $649 | 3–4 hours |
| Two storey, low pitch | 2,000 sq ft | $549 – $749 | 4 hours |
| Two storey, steep pitch | 2,000 sq ft | $649 – $899 | 4–5 hours |
| Concrete tile | 2,000 sq ft | $599 – $949 | 4–5 hours |
| Metal roof | 2,000 sq ft | $499 – $799 | 3–4 hours |
How often, and what happens after
In Jacksonville, plan on cleaning a roof every two to three years. Streaks generally start to reappear at around 18 months on shaded north-facing slopes and closer to three years on open, sun-exposed roofs.
Zinc or copper strips fitted at the ridge slow regrowth — rainwater carries trace metal ions down the slope, which algae will not tolerate. It is not a permanent fix and it works less well on very wide roofs, where the lower courses get a weaker dose, but it does buy time.
What's included in every job
No line items appear on the invoice that weren't on the quote. Everything below is part of the price:
- Full no-pressure soft wash of the roof surface
- Complete pre-wet and post-rinse of all landscaping and gutters
- Gutter exteriors cleaned as part of the rinse-down
- Downspouts flushed so runoff does not stain the driveway
- Free roof condition report with photos of anything we spot
Pitch, height and tile type change the figure more than area does. Read more in our Jacksonville pricing guide, or see what to ask before hiring anyone.
Expert tips from our crew
Things worth knowing whether or not you hire anyone. Several of these will save you money, and a couple of them will save you from a repair bill.
Check your gutters after anyone cleans your roof
A gutter full of coloured grit means the roof was pressure washed, not soft washed, and your shingles have lost their UV shield. It is the fastest way to tell what actually happened up there.
Trim the limbs before you book the clean
Overhanging branches drop debris that holds moisture against the shingles, and the shade stops the roof drying. Cutting them back extends the result more than any treatment we can apply.
Ask about zinc or copper ridge strips
Rainwater carries trace metal ions down the slope and algae will not tolerate them. It works well on the upper courses and less well on very wide roofs, but it genuinely buys you time.
Photograph your roof once a year
Streaking creeps up so gradually that you stop seeing it. Compare this year's photo with one from three years ago — most people are surprised how far it has gone.
