What the black streaks actually are
The dark streaks on roofs across Tampa Bay are mostly a type of algae called Gloeocapsa magma. It feeds on the limestone filler in asphalt shingles and grows well in warm, humid weather. It spreads from roof to roof on the wind, starts on north-facing slopes that stay damp longest, and darkens over time as it builds a protective coating against the sun. Lichen and moss, which show up as green or gray patches, often follow on shaded sections.
Besides looking bad, a dark roof absorbs more heat, and lichen and moss hold moisture against the roofing material.
Why we do not pressure wash roofs
High-pressure water on an asphalt shingle roof strips the protective granules, shortening its life, and can drive water under the shingle edges. On concrete tile, it can crack tiles and blast off any coating. Most shingle manufacturers recommend against pressure washing for that reason.
Soft washing uses a cleaning solution, typically diluted sodium hypochlorite with a surfactant to help it cling, applied at roughly garden-hose pressure. The solution kills the algae, and rain over the following weeks finishes rinsing away the residue. On tile, a gentle rinse right after treatment removes most of the staining.
Shingle roofs versus tile roofs
Shingles are treated top to bottom with the solution and then left alone, and most of the black disappears within minutes. Heavier growth may need a second application.
Concrete tile roofs are porous and hold more growth in their texture, so they get a slightly longer dwell time and a careful low-pressure rinse. We walk tile roofs only where we must, stepping on the lower part of each tile where it is supported, since stepping on the middle can crack it. If tiles are already cracked or slipped, we photograph them for your roofer. Once clean, a tile roof can be coated through tile roof painting if the color has faded.
Protecting the house below
Runoff from the roof is the main risk to plants, so we soak beds and shrubs before treatment, keep them wet during, and rinse them again afterward. Gutters are flushed so solution does not sit in them, and downspouts are directed away from plant beds. We also cover outdoor light fixtures and rinse windows, lanai screens and the pool cage when runoff reaches them. Walls stained by roof runoff can be cleaned the same day with soft washing of the walls.
Call us when you notice
- Black streaks are spreading down the north slope
- Green moss or gray lichen on shaded sections
- Tile roof looks dark and blotchy compared to neighbors
- HOA notice to clean the roof
- You are planning to sell and want curb appeal
How a roof soft washing job runs
Roof survey
We check roof type, slope, growth level and any broken tiles or loose shingles from the ground and ladder.
Protect the yard
Plants are soaked, fixtures covered, and gutters and downspouts checked.
Apply solution
The cleaning solution is applied at low pressure from the bottom up, covering every stained area.
Dwell and rinse
The solution works for a set time, then tile roofs are rinsed gently, while shingles are left to weather clean.
Final rinse below
Plants, walls, windows and screens are rinsed, and the gutters flushed clean.