Algae Discoloration and Your Roof

Algae Discoloration on the Roof

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For roofs that either get a lot of shade or are constantly battling humid and hot conditions moss and algae can be a problem. Algae and or moss often show up on the east facing side of the roof but can also show up on other faces as well based on the amount of shade, heat, and humidity. There are a few options to preventing the algae or black streaks from appearing on roofs. The most efficient options involve algae resistant roof shingles.

Algae resistant shingles are specially made shingles that prevent algae growth. They look like normal shingles

and to the naked eye seem to be the same but they are manufactured a little differently.

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.

 How Does a Roof Get Algae?

Algae spread from one infected roof to another via airborne 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?


 What Solutions Do I Have?

Algae Discoloration on the Roof
  • Install Algae Resistant Shingles which have a specially formulated granule that inhibits algae growth, keeping your roof looking new for years to come.
  • If a new roof is not an option, you can clean the roof with a special mixture. That mixture is: 4 gallons of water, 1 gallon of bleach and 1 cup of TSP (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 the shingles. Some roof cleaning companies offer this service. However, it is not recommended as it may dislodge granules, which can lead to premature shingle failure.

Algae require moisture and proper temperatures 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 the northern exposures of the roof since this exposure generally receives less sunlight. Algae are well adapted to extreme conditions.