What’s That Black Stain on My Roof?

Did you Know Those Black Stains Are Alive?

Black Stained RoofThose black stains on your roof are Algae. AlgaeĀ appears as dark stains on shingles and 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 spreads from one infected roof to another via airborne spores.

These spores go wherever the wind takes them and then land randomly on a roof and take root.

A protective sheath creates the dark color the algae takes on to protect itself from UV rays.

How Does It Grow?

Algae requires moisture and proper temperatures to grow. Dew is the primary moisture source. Algae is found predominately in the Southeast, but it can and will grow nationwide. It generally grows on the northern exposures of the roof surfaces since this exposure tends to receive less sunlight.

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 aging and failure.

What Solutions Do I Have?

  1. Take safety precautions when working on the roofInstall Algae Resistant Shingles such as GAF-Elk’s shingles which have a specially formulated granule that inhibits algae growth, keeping you 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: 4 gallons of water, 1 gallon of bleach and 1 cup of TSP (Tri-Sodium Phosphate or acceptable phosphate free substitute )found in many home centers. Apply this mixture with a garden sprayer, let sit on the roof surface for up to 20 minutes, then rinse with low pressure water. Be sure to protect the shrubs below. Remember, the roof surface will become slippery when wet – be careful!

If you need a new roof, give us a call and we’ll be happy to give you a free, onsite estimate.

**originally published 11/12/10

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