To prevent moss or algae growth, limit shade and clear any debris that could lead to moisture on your roof. You can also choose algae-resistant shingles, which will also help with moss.
Another option is to install a metal strip, such as copper, zinc, or galvanized metal, on the ridge of the roof, which will oxidize and wash down the roof plane when it rains, making it less habitable for moss, algae, and lichen. Alternatively, you can clean your roof by sweeping and blowing it once or twice a year when dry and applying baking soda at the ridge line in late summer, which will raise the pH and deter moss growth. Baking soda may require more than one application per year and may take several weeks to kill existing moss.
If you have noticed the presence of algae or moss on your roof, do not take any heroic actions trying to get rid of this problem. You may end up hurting yourself. Let the roofing contractors from Big Al’s Roofing perform a thorough cleaning of your roof and get it looking as good as new.