For best results:
Have me clean off the moss
and then coat the roof with
zinc sulphate monohydrate
to kill the moss spores that
cannot be seen, but will
begin to grow and multiply
immediately after cleaning.
As you well know, roof moss is a real problem in the Pacific Northwest. It roots into the shingles, drying them out, causing them to become brittle, and eventually to crack and leak. Moss also grows along the edges of shingles, raising them and drying them out even more rapidly.
Any metal will kill moss, and I use zinc to kill roof moss. But killing the moss does not remove it. Even dead, it still lies there, holding moisture against the shingles, deteriorating them. So I recommend cleaning the moss off first, and then coating the roof with zinc sulphate monohydrate to kill the moss spores which cannot be seen but which will begin to grow and multiply immediately after cleaning.