Not all moss is created equal. In fact some moss is more destructive than others. Asphalt shingle roofs (the non-wood looking kind), grow moss more frequently as a result of the roofing material. Cedar or shake roofs typically attract algae and fungus (which turns the roof black). What I learned from Patrick D. Morin is if your cedar or shake wood roof has moss, especially the kind shown in the video below, you’ve got some serious problems.
Patrick Morin, Roof Life of Oregon, March 31st 2010. We’re on a roof that’s about 15 to 18 years old under a super heavy canopy of maple trees, elm trees, some 200 foot fir trees, and this roof gets buried in debris. The homeowner is constantly blowing it off. When we’re talking about different types of moss that tends to grow, most of you have architectural asphalt shingles and you get the rows and rows of the rolly polly type moss. There’s also a second type of moss that grows on these shake roofs especially in this environment. It almost has a root system, in fact it does, as I scrape it off you can hear the roots breaking. It’s actually growing in the wood. This is actively growing because it’s eating the wood and using it as a food source.
It’s incredible to think that your cedar or shake roof can produce wood eating moss as a result of your environment. If you live in a shaded area with large trees and have a cedar or shake roof you need to have your roof inspected every five years to prevent a problem like this from happening.