Drive through almost any Central Florida community and you will see roofs with dark streaks running down from the ridge. They are not dirt, soot or shingles wearing out. They are living growth, and they are one of the most common reasons an HOA board schedules a cleaning.
This guide explains what the streaks are, why they keep coming back, and why the method matters more on a roof than anywhere else on the property.
What the black streaks are
The streaks are a type of algae. The Asphalt Roofing Manufacturers Association names Gloeocapsa magma as the most common of several species behind roof discoloration, and notes that it thrives in warm, humid conditions. Central Florida has those conditions for most of the year.
The growth usually shows first on north-facing slopes and on roofs shaded by trees, where the surface stays damp longest after rain and morning dew. From there it spreads, and the streaks darken as it does.
On tile and metal roofs the same conditions bring algae, mildew and sometimes moss and lichen in the shaded areas.
Why a roof must never be pressure washed
This is the one surface where the wrong method does real, expensive damage.
- Shingles lose their granules. The granules on an asphalt shingle protect it from the sun. The roofing industry's guidance is explicit: do not use a power washer, or even a brush or broom, to clean algae off a shingle roof.
- Tiles crack and loosen. High pressure on a tile roof can break tiles, shift them, and drive water underneath them. That is how a cleaning turns into a leak.
- The streaks come back faster. Pressure blasts the visible growth off but does not kill what is left in the surface, so it regrows quickly.
If a contractor plans to put a pressure wand on your roof, find another contractor.
How soft washing works
Soft washing treats the growth with chemistry instead of force.
- Protect the landscaping. Plants around the building are wetted down before the roof is treated and rinsed again afterwards.
- Apply the cleaning solution at low pressure. Soft wash solutions are typically based on sodium hypochlorite, the same active ingredient the roofing industry recommends, and they kill the algae where it grows.
- Give it time. The solution needs dwell time to work. This is what separates a cleaning that lasts from one that does not.
- Rinse gently. A low-pressure rinse clears the solution. Nothing is blasted off.
The streaks often fade further over the days after the cleaning, as the dead growth washes away in the rain.
How often to clean
Even a properly cleaned roof will grow algae again. The roofing industry says plainly that the effect of cleaning is temporary and the discoloration may come back. In Central Florida, we recommend cleaning most roofs about every two years, which keeps regrowth light and each cleaning routine.
Algae-resistant shingles, which have copper in the granules, slow regrowth down. They do not stop it entirely, especially under trees.
Before you book: check the roof's guidance
Some shingle manufacturers specify which cleaning methods and chemicals they approve. The roofing industry advises using other chemicals or methods only with the manufacturer's approval. If your roofs are under warranty, it is worth checking, and a good contractor will ask.
You can read the roofing industry's guidance on algae discoloration.
How we clean roofs
Green Earth Power Wash Orlando soft washes barrel tile, shingle and metal roofs for HOA and condo communities across Orlando and Central Florida, with landscaping protected throughout and no high pressure on any roof. See our roof soft washing and HOA community pages, or request a free estimate.