What the streaks actually are
Gloeocapsa magma, an airborne algae that feeds on the limestone filler in asphalt shingles. It holds moisture against the roof surface, accelerating granule loss and shortening roof life. Moss is worse: it develops roots that lift tiles and channel water sideways underneath them.
Never pressure-wash a roof
High pressure strips protective granules off shingles and drives water under tile. It looks clean for a season and costs years of roof life. Roofs get a low-pressure application of cleaning solution that kills the growth at the root, then a gentle rinse.
Minimal foot traffic
Walking on clay or concrete tile cracks it. Walking on hot asphalt shingle displaces granules. Most of our roof work is done from ladders and extension equipment for exactly that reason.
Why it comes back slower
Knocking growth off mechanically leaves the roots and it returns within a season. Killing it chemically means regrowth takes considerably longer. That's the difference between cleaning a roof yearly and cleaning it every few years.
Common questions
Will you walk on my roof?
As little as possible. Most work is done from ladders and extension equipment.
Is roof cleaning safe for tile?
Yes, with low pressure. Clay and concrete tile are brittle and crack under foot traffic and high-pressure impact, which is why we avoid both.
Do you clean gutters at the same time?
Yes, and it makes sense to combine them since roof debris ends up in the gutters anyway.
How often does a roof need cleaning?
A properly soft-washed roof should hold for several years. If yours needs it annually, it wasn't cleaned correctly.