Since I've been trying to do my own wash business I've looked at so many homes that I've noticed dirty roofs on. Some of which are REAL bad, and I can only imagine how long they've been that way. Is there any cases where a roof has had growth for so long it wouldn't be smart to sell a wash? How would you tell outside of seeing damaged shingles? Let's say a house has no noticeable shingle damage, but has been black for years, would doing a wash potentially remove granules that have deteriorated over a long period of time? Has anyone ever came across a roof so dirty that it just didn't come clean, or that they decided not to even bother with it?

Thanks!