How to Avoid Black Streaks on Your Shingled Roof

Nothing is worse than looking up at your roof to find that it is covered with black streaks and stains. These stains can mar the appearance of your roof and make even a brand-new roof look old. But where do these black streaks come from, and how can you avoid them?

Causes of Black Streaks on Roofs

The black streaks that appear on roofs are not actually a stain – they are the result of algae growth on the shingles. The type of algae that causes these black streaks is called Gloeocapsa magma, and it is a hardy variety of blue-green algae. This type of algae feeds on the minerals found in certain types of roofing shingles and thrives in damp conditions – this is why black stains are most commonly seen on north-facing roof sections and those that do not see a lot of direct sunlight. The algae responsible for these black streaks do not actually damage the shingles, but they can be unsightly. Fortunately, there are some simple ways to remove the stains and prevent them from recurring.

How to Remove Black Streaks

It is not difficult to remove black streaks from your shingles, but you should be aware that unless you take preventive measures after cleaning, the streaks are likely to come back. You may be able to find a cleaning solution at your local home improvement store that is designed to remove black streaks, or you can make the solution yourself. To make your own cleaning solution, combine 1 quart of bleach with 1 gallon of water and add ¼ cup trisodium phosphate, or some other type of heavy-duty cleaner.
Once you’ve mixed your solution, pour it into a pump-type sprayer and use it to thoroughly wet down the roof. Let the solution set for about 15 minutes after applying so it soaks into the shingles. Next, rinse the solution away with a high-powered hose. As you rinse away the solution, the algae should come away with it, leaving you with clean shingles.

Tips for Avoiding Roof Stains

If you truly want to avoid black stains on your shingles, you may want to switch to an algae-resistant shingle material. Algae-resistant shingles are made with copper granules mixed into the shingle material, which helps prevent algae growth. If your roof is in disrepair and needs to be replaced anyway, this may be your best option. For those who do not want to redo an entire roof, installing copper or zinc strips along the top of your roof may be a more cost-effective solution. When water hits the copper or zinc strips, it will create a solution that flows down the shingles, helping prevent moss, fungus, and algae from growing. This solution only works for preventing algae growth – it won’t get rid of any existing black streaks.

Tips for Avoiding Roof Stains

Black streaks on your shingles may not be damaging your roof, but they certainly can detract from the appearance of your home. By dousing your roof with a bleach-and-water solution, you can remove the streaks. By installing copper or zinc strips on the roof, you can prevent them from coming back.