"What is this black stuff on my roof?"
It's a question many homeowners all over the country are asking -- and it's a question Vincent R. Valles, Sr. hears often.
The answer is mold and fungus, says Valles, who is founder and president of Dur-A-Shield International, Inc., a Palm Coast, Fla.-based company that specializes in exterior restoration and protection.
Because the black growth (fungus) covering roofs lacks chlorophyll, it is unable to manufacture food from raw materials. So, it must get nutrition from some form of organic matter. To thrive, this particular fungus, called saprophyte, also requires a warm, humid environment such as your roof.
Saprophytic fungus normally begins its life cycle as an airborne spore that settles on asphalt-shingle roofs. The spores on the northern exposure of the roof stand a better chance of survival because that portion of the roof is the last part to dry after a rain or morning dew. This raises the humidity on the surface of the shingle, thus creating a perfect feeding and breeding ground.
The tar used in roofing is fossilized, dead organic matter -- and a food source for saprophyte fungus. Asphalt, at the granule base, is normally consumed first. Once these granules dislodge, accelerated deterioration will occur. Ceramic granules represent the outer hard shell that protects against hail and other falling debris. Ceramic granules protect against damaging UV radiation and insulate the roof against extreme heat.
Mold and fungus on a roof also act as a sponge to absorb the sun's heat, which causes a rise in the temperature inside a home or building, creating higher air conditioning bills.
Aesthetically, a home with fungus on the roof not only looks bad, but it can decrease the property value -- and make it more difficult to sell the home. A home with a dirty roof takes longer to sell than one with a clean roof.
"These micro-organisms could also potentially be harmful to your health," says Valles. "Of course, not all mold and algae pose a health danger, but some are harmful, especially for senior citizens and people who suffer from asthma and respiratory problems."
The mold spores, which are on your roof, can get inside your home because they end up on the driveway and walkways from rain, and are easily tracked inside.
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