After seeing all the Crustose on roofs this year, I wanted to write a quick article with a few pictures. Roof Cleaning in Raleigh had an early start this year with a run of good weather. Dirty roofs are everywhere and we have been busy.
Crustose is a form of lichen that grows on your roof, along with the algae. It actually uses the algae and parts of the roof as a substrate, or base to grow on. It shows up on your roof after the algae has matured and turned to the black streaking mess. On very dirty roofs, it is not easy to see unless your are really looking. But once it is clean, it is right there, plain as day.
Crustose is a very hard lichen and does not come off during an initial roof cleaning. Once the cleaning is done, the black roof staining is gone, but the crustose is still there, looking like a bunch of bird droppings. I used to call it “concrete lichen” because it was that hard. After the roof cleaning, it is dead and the decomposition process will begin. Over a period of time, with rain, it will begin to flake off and eventually disappear.