Have you noticed some black streaking on your roof lately? Or maybe you have seen it on someone else’s roof and wondered what it was. It happens on asphalt shingles and is blue-green algae. While it is not a glamorous sight to see, it is very common; so if it is on your roof, do not worry as there are ways to remove it and prevent it.
Knowing what causes these ugly black streaks can help you understand how to prevent them and get rid of them if they are already appearing. Algae starts to grow and accumulate on the shingles and then a harder outer shell starts to form, protecting the algae from the sun, which is the streaking that you see. As time goes on, it will get worse because moisture gets trapped, especially after rain and snow.
Streaking seems to be more common these days and that is because manufacturers of shingles are looking to save money and use fillers like limestone and fiberglass combined with the asphalt. Limestone is what algae use as their food source.
Of course, one easy way to get rid of, and even prevent, these streaks is to use algae-resistant shingles. If your roof is old and in need of replacing, this may be a justifiable option for you. If your roof does not require a replacement, then you don’t want to spend unnecessary funds. Luckily, you can clean your roof periodically to get rid of the black streaking.
If you decide to do it yourself, make a cleaning solution consisting of 1 cup of trisodium phosphate (Lowe’s or Home Depot should have this), 1 gallon of bleach, and 5 gallons of water. Be sure to use gloves and eye protection. Use a garden sprayer to spray the solution on the shingles and rinse after 15-20 minutes.
Please be aware that a lot of warranties will be voided if you do this yourself, so it is probably a good plan to have the cleaning done by a trusted roofing professional.