Austin roof cleaning that clears the streaks.

The black streaks running down a Central Texas roof are not dirt and they are not stains. They are a living organism, a hardy blue green algae that feeds on the limestone filler in modern asphalt shingles. That is why the streaks run downward, and why they show worst on the north facing slope that stays damp longest.

It matters because you cannot fix a living thing by scrubbing harder. Pressure washing a roof strips the granules off the shingles, and those granules are the entire protective layer standing between the asphalt underneath and the Texas sun. Take them off and you have not cleaned the roof, you have shortened its life and quite possibly voided the manufacturer warranty at the same time.

So a roof is washed at roughly the pressure of a garden hose. The cleaning solution does the work, killing the growth at the root so it releases and then rinses away over the following days rather than being blasted off in the moment. Done properly the roof keeps looking better for weeks after we leave.

The other half of the job is everything that is not the roof. Runoff has to be controlled and the landscaping below has to be protected and rinsed, because the solution that clears algae will also burn plants. If a roof cleaning quote does not mention protecting what is underneath, that is worth asking about before anyone gets on the roof.