Tile, shingle and metal roofs treated at low pressure to kill algae at the root — the method roofing manufacturers actually approve.
Those black streaks running down a South Florida roof are a cyanobacteria called Gloeocapsa magma. It feeds on the limestone filler in asphalt shingles and thrives in heat and humidity, which is why roofs here streak faster than almost anywhere in the country. It is a living organism, not a stain — and that changes how it has to be dealt with.
High pressure on an asphalt shingle strips the protective granule layer that shields the asphalt from UV. Those granules do not grow back, and losing them shortens the life of the roof measurably. On tile it drives water under the tiles and can crack them; on older tile it breaks them outright. Most shingle manufacturers void the warranty on a roof that has been pressure washed, and the industry standard method is low-pressure soft washing.
Soft washing applies a treatment at roughly garden-hose pressure. It kills the organism at the root and the roof continues to clear over the following days as rain rinses the dead growth away.
Everything that comes off a roof lands on the landscaping, driveway and pool deck underneath it. Plants get saturated with water before work starts and rinsed thoroughly afterward, and the surrounding hardscape gets rinsed down as part of the job. Skipping this step is the single most common cause of plant damage on roof cleaning jobs.
A roof does not go from black to bright on the walk-around. The treatment kills the growth immediately, but full visual clearing typically takes a few days to a couple of weeks depending on rain. Anyone promising an instant transformation on a heavily streaked roof is either pressure washing it or overselling.
We also will not walk every roof. Steep pitch, brittle older tile, or a roof already in poor condition can be treated from ladders and extension equipment instead — or we will tell you it is not a job we should take.
Send the address and a photo from the street. We will tell you honestly what it needs.
