I've been helping a friend of my parents for a number of years now do odds and ends around her house.
During my last visit a couple weekends ago she asked me to tackle the moss problem that has begun growing on her garage and porch roofs.
The first two pictures you can see that I sprayed the garage roof with a mixture of bleach and water. I would have preferred more bleach but had to work with what I had.
Her porch roof is really a mossy mess, as you can see. This is on the list for my next visit. I instructed her to pick up four gallons of bleach, which I'll use to his this spot and revisit the garage roof with again.
I've not heard from her since apply so not sure how successful this exercise was. Time will tell. I also cut back a number of branches that were blocking the sunlight from getting through. Hoping this will help too.