What are the black streaks I see on older asphalt composition roofs?
Those streaks are caused by algae growing on your roof. The algae itself is uglier than it is harmful, but it can promote future moss growth. You’re probably wondering what you can do to prevent it. There are a number of products that kill the algae growth along with several types of asphalt composition roofs that come with copper coated granules. These granules will help prevent the algae growth before it starts and have 10- to 20-year warranties, providing a wonderful long term answer to your algae problem.
