roof stains

Roof Stains: Everything You Need to Know!

Are you perplexed by roof stains that look like this?

Roof stain

The culprit is an algae called Gloeocapsa Magma. This blue-green algae, found in the Eastern United States, is spread by airborne spores. It appears in streaks or patches of slime on your roof. While this algae does not pose a danger to your home or health like mold does, it’s not something you should ignore. You should clean and treat the algae.

These stains are often attributed to dirt, defective shingles, mold, or mildew, but experts think the increased use of crushed limestone in asphalt shingles, used as a filler, is actually to blame.

How to Clean Roof Stains

Cleaning the algae from your roof involves oxygen bleach. Spray wash your roof with a mix of equal parts water and bleach to get rid of the algae. Do not use a pressure washer as they are likely to damage the shingles. You can also use a trisodium phosphate solution. It’s best to have a professional tackle this job.

Preventing Roof Stains

To prevent the algae from returning, insert strips or sheets of zinc or copper under the shingles closest to the roof peak (above the stained area). Leave 1-2” exposed so that when it rains, the rainwater washes the metallic atoms over the roof below. These atoms will kill any algae trying to latch on to your shingles. The best part? You’ll kill future algae without having to lift a finger!

You can also install algae-resistant shingles. These shingles cost a bit more than regular shingles, but you’ll save money by not paying for cleaning or installing of the metal sheets.

Algae thrives in the shade, so trim nearby trees to allow more sunlight to reach the roof. Doing so will slow future algae growth. Moss grows in the shade of trees, too so you’ll be preventing its growth as well.

Other Causes of Roof Stains

Other issues can cause roof stains. Below are some of the main culprits — beyond algae.Rusted roof stains

  • Red or brown rust stains around chimneys are also common. Clean the area with oxalic acid to prevent future rust.
  • White stains on slate roofs can come from salt stains from rainwater (efflorescence).
  • Vegetation stains may appear near trees from seeds, berries, leaves, and other debris that fall and decay on your roof.
  • Water stains from leaks. If the stain is damp, check the attic or ceiling below the stain for a leak.
  • Light spots on roof shingles may appear as the roof ages. Check your gutters for signs of asphalt granules that have washed away. If you do find them, plan on replacing your roof soon.

The Bottom Line

In most cases, your roof stains can be attributed to algae. While it’s harmless, it takes away from your home’s curb appeal and should be removed. With some elbow grease and a little bit of work to install metal or copper on your roof, you can prevent future stains. Also, try to maintain as much sunlight on your roof as possible to prevent both algae and moss.

For more tips on maintaining your roof, check out our related posts.

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