Roof Cleaning Services
Odds are that "dirt" on your roof isn't all "dirt."
Some of that "dirt" is probably alive.
Often, black or very dark stains on a roof are caused by a type of blue-green algae.
That's bad enough. However, that algae retains water as it grows, which promotes the development and growth of other roof contaminants such as fungi.
The algae spores feed on the limestone in asphalt shingles and the actual dirt on tile roofs.
So those black or dark stains on your roof are probably home to a number of molds and fungi in addition to algae.
Fungi are normally found on the north-facing slopes of roofs, especially ashphalt shingle roofs, because these are the coolest and dampest surfaces for the longest periods of time during a day.
Roofing tar is a major component of asphalt shingles as well as most types of flat roofing material. Roofing tar is made from crude oil. Crude oil is fossilized organic matter, which is a good food source for fungi (as is the algae). And that's one reason fungi love asphalt-based roofing systems.