I have an asphalt roof. Prob. gets about 3 - 4 hours of sun a day. I have black stains, which I'm assuming is mold. There were a few spots that get very little sun and those areas had some actual moss. I think the wet and forget killed the moss but I did try to knock it off when I on the ladder spraying on the wet and forget so a lot of it prob. just washed away with the rain.
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