The following examination of roof stains and their potential effects on health was written by Dr. Victor H. Morgenroth

Dr. Morgenroth is a Keys Gate resident who is a semi-retired, adjunct professor of neurology at UM. He was a principal administrator in the Environment Health and Safety 
Division of the Organization for Economic Cooperation and Development (OECD) for 20 
years; prior to that he was a Group Leader in the Toxicology Division at the Center for
 Food Safety and Nutrition in the US Food and Drug Administration (FDA). Previously,
 he was on the faculty of several medical schools in neurology, pharmacology and
 psychiatry.

Having your roof cleaned actually makes sense.... It isn’t just aesthetics. While people like to say that dirty roofs lower a property’s value and may make 
it hard to sell, the “dirt” on a roof actually shortens its life span and can even present a health hazard.
 Furthermore, the “dark stains” on a roof 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.
 The dirt isn’t just dust – It’s alive. Some of the black or very dark roof stains are caused by a resilient type of algae, Gloeocapsa magma (a type of blue-green algae commonly found in climates with
warm, humid summers). The algae grow in standing water, as well as in our lakes and ponds. The
 algal spores are carried to our roofs from the water sources by the wind and birds, and then from roof
 to roof where it grows and feeds on the limestone filler in asphalt shingles and the real dirt on tile 
roofs may be in some cases the tiles themselves. Worse still, as the algae grow, they retain water and 
foster the growth of other roof inhabitants.

The black stains are also very likely to harbor a number of molds or fungi. Unlike algae the fungi on 
our roofs lacks chlorophyll. They are unable to manufacture food from raw materials. So, it must get 
nutrition from some form of organic matter. To thrive, these heterotrophs, who used to be called
saprophytes, also require a warm, humid environment.

Fungi normally begin their life cycle as an airborne spore that settles on roofs, especially the asphalt shingle 
ones. 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 an important food source for 
fungi. 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. So you can understand that their
 dislodgement by the growing fungal colonies can be detrimental to our roofs’ longevity.
 Surprisingly, the blue-green algae are also food for the fungi.

While not all mold (fungi) and algae pose a health danger, some are harmful, especially for us older 
folks, younger children and people who suffer from asthma and respiratory problems. Their 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. They can even be drawn into our air conditioning systems and
 eventually populate our ducts.

Different mold species can have varying health effects, but it is important to remember that any
 excessive mold growth needs to be taken care of, regardless of the species. Any excessive mold growth can lead to increased allergies, toxicity, and house/building structural problems.
 While “sick building syndrome” has been talked about
 frequently in the media, it isn’t always reported that this syndrome is often caused by faulty or leaking
roof assemblies that result in fungal infestations. It isn’t, as reported, always due to chemicals in 
carpeting.

Don’t Panic!

Most of us have immune systems that are fully capable of resisting the effects of fungi described
 below. As a result it would be highly unlikely for any of us to suffer any of the ill effects described.
 But if fungal colonies are allowed to persist and multiply then the high concentrations of the molds
and their volatile organic chemical metabolites might be sufficient to increase the risks from our 
exposure to them.

CLICK BOX TO ENLARGE