Preventing ugly black streaks on your roof isn’t easy but here are some things you can do to help prevent it. First, make sure all tree branches are at least 3 to 4 feet off the roof (5 to 6 would be ideal). Next, make sure all of your gutters are flowing properly and free of any debris. Over time houses settle and sometimes the water doesn’t flow to the down spouts and allows standing water. If you notice standing water in a section of your gutter a down spout might be able to be installed to relieve the problem.
This strain of algae (gloeocapsa magma) loves moisture and shade. The last thing you can do is spray a protectant on in the spring and fall. The stains start at the gutter and works its way to the top of your roof. Spray the protectant on the bottom 3 tabs of shingles, in the valleys, and in the areas that get little sunlight. A protectant you can buy in the big box stores that works really well is Concrobium Mold Control. Doing these things will help you get the life out of your roof and keep it looking great for a long time. Warning, being on a ladder or roof can be very dangerous and a professional may be needed.