Roof Cleaning Off Black Streaks or Zinc Metal Strips

Q. We have a charcoal colored roof that is almost ten years old. The east end of the house did not get much sunlight until Friday, March 30. Our neighbor had three large oak trees and the sun didn't get to our roof very well. They had the trees removed yesterday, so we will get lots of light and sun on the roof now. Is there anything we can do to clean the mold and/or mildew streaks off the shingles?

A. The mold or algae on the roof shingles is most likely an algae called gloeocapsa magma, or it is more commonly referred to as blue-green or black algae. Algae is actually a solid deposit of spores and dirt.

Wash roof shingles with a soft bristle brush or broom (no metal brushes) with a detergent like TSP, Spic & Span, Top Job, Simple Green etc. This removes most of the solids. Fully rinse the roof.

It's unlikely all of the discoloration will come off with washing. Tannic acid in the oak trees can stain the roof without mold and mildew. Washing is your best way to improve the look of your roof.

There are also algae & mold resistant roof shingles available for humid climates near oceans and rainy areas of the globe.

Another treatment for avoiding the black streaks is to install Zinc metal strips at the top of your roof near the ridge caps above the algae prone areas. These zinc metal strips affect the water and help avoid the black roof streaks in many cases.

My company provides this black streak roof cleaning service and will take care of this for you. Phone the Mosby Building Arts office at 314-909-1800 or click here for a contact information.

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