While the moss won't do damage, at least I think not, it did make one house listed for sale problematic, until, we suggested getting it removed. I was there that day overseeing it, and, the contractors used a push broom, and, a mixture which it appeared to be, of just water and bleach. They did cover the surrounding plants on the ground with plastic. When they finished the roof looked great and was not a problem, any longer. I hope this helps.