We have moss like you would not believe in the Northwest. Zinc strips work OK. Zinc Sulphate powder (moss-b-ware, moss out) works also. Generally the best idea is to kill it with zinc powder or a weak solution of bleach. then after a few months when it is all brown sweep it off, or use a garden hose (if you can walk on the roof) if it is too steep then most of it will come off in the rain.
Don't be the guy who falls off his roof and is killed or maimed because of moss
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