Q. Why does my roof look dirty? Is there a way to clean it?
A. Black stains and streaks on asphalt shingles are caused by bacteria called Gloeocapsa Magma (often referred to as Algae or Roof Mold). This is typically found on the side of the house where the sun does not hit the roof directly or the roof is shaded by trees.
The algae feed on the limestone that is used as filler in asphalt shingles. When it rains, the algae is spread, causing black streaks and stains. These stains are typically not harmful to a roof, they are just aesthetically unappealing.
If these stains are left untreated, lichen and moss may eventually develop. When lichen and moss are allowed to grow, they can damage the shingles due to the growth of a root system.
Not only do the stains affect the curb appeal of a home, buyers may also perceive the stains as a problem with the roof or believe the roof to be older than it actually is. Roof cleaning is always recommended prior to listing when it dramatically impacts the appearance of the home.
There are companies that specialize in soft wash roof cleaning and there are DIY products available. However we recommend staying off the roof and leaving such a job to professionals. And whatever you do, never use a power washer on your roof.
There are zinc strips available which can be installed on the roof. When rained on, zinc oxide forms and runs down the roof killing the algae. However, there are mixed reviews on the effectiveness of the zinc oxide strips. Additionally, many zinc oxide strips are incorrectly installed compromising the integrity of the roof.
It is recommended to trim any trees overhanging the roof to allow the sun to dry out the roof and kill the bacteria naturally.
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The Scott Loper Team
Scott & Lisa Loper