Roof Stains

How Roof Stains Occur

Have you noticed black stains on your roof? Most people believe that these black stains are caused by the natural process of the roof shingles breaking down over time. A majority of roofs are replaced not because of structural damage or deterioration, but because they are unsightly.

These black stains are caused by algae that is eating the crushed limestone granules used to provide strength to the fiberglass backing of the shingles. The algae is retaining moisture and eventually the limestone granules will lose their adhesive properties and fall off. Loss of the limestone granules will cause the shingles to fall apart exposing the roof structure. The stains are caused by the waste material released by the algae, mold, and fungi.


Install Zinc / Copper Strips

There are several remedies available to homeowners who are experiencing this unsightly problem. One possible solution is to install zinc or copper strips on the roof. The theory behind this is that the copper or zinc ions will wash down the roof during a rainstorm and kill the algae, mold, and fungi. The drawback to this method is the fact that it is expensive and is only a short term solution.

Chemical Use

Another solution would be to clean the roof using a deck cleaner, an oxygen based cleaner, a sodium per carbonate compound, or common laundry bleach. There are also a number of commercially available roof stain removing chemicals available for use. 

Hire a Contractor

Another possible solution would be to hire a roofing contractor that specializes in roof cleaning. If you plan on having your roof replaced, you may want to consider using an algae resistant shingle. These shingles are available from most shingle manufacturers.


  • Always read the directions on chemical products and be aware that certain ones may be harmful to plants, pets, and children.
  • Always use extreme caution while working on the roof and never try to walk on a wet roof surface, as serious injuries can occur.
  • Never use a power washer to clean your roof, as this could result in substantial damage to the shingles and may lead to replacement. When washing your roof, you should always use a low pressure garden hose and disperse any chemicals using a garden sprayer attachment.