Algae Staining On Shingled Roof Surfaces

Sep 17, 2010 | How To Articles

What are those black stains on the roof?

Those black stains are Algae. Algae appear as dark stains on shingles that usually cover more area on the lower section of the roof and taper as they reach the ridge. While it may not impact the overall life of the roof, it could be an indication of other roof problems.

How does a roof get algae?

Algae spread from one infected roof to another via air born spores. These spores land randomly on a roof and take root. A protective sheath creates the dark color the algae forms to protect itself from UV rays.

How does it grow?

Algae require moisture and proper temperature to grow. Dew is the primary moisture source. Algae are found predominantly in the southeast, but it can and will grow nationwide. The algae generally grow on Northern exposures of the roof since this exposure generally receives less sunlight. Algae are well adapted to extreme conditions.

What Solutions do I have?

  1. Install Algae resistant shingles, such as GAF-Elk’s shingles which have a specially formulated granule that inhibit algae growth, keeping your roof looking new for years to come.
  2. If a new roof is not an option, GAF-Elk recommends cleaning the roof with a special mixture. That mixture is: 4 gallons of water, 1 gallon of bleach and 1 cup of TPS (tri-Sodium Phosphate- or acceptable phosphate-free substitute) found at many home centers. Apply this mixture with a garden sprayer, let sit on the roof surface for up to 20 minutes, and rinse with low pressure water. Be sure to protect any shrubs below. Remember, the roof surface will become slippery when wet, be careful!!!

What not to do!

Do not power wash the shingles to clean them. Some roof cleaning companies offer this service. However, it is not recommended as it may dislodge granules, which can lead to premature shingle failure.

Where can I get more information?

Your shingle manufacturer’s Technical Service Department can assist you with these and other questions you may have regarding your new roof installation.

Most shingles we install are GAF-Elk. Their Technical Service Department can be contacted at 800-ROOF-411 (800-766-3411). Also, the GAF-Elk website is a great resource for just about any question you may have or for additional information you may require. That site is at

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