Understanding The Dangers of Roof Mold

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Understanding the dangers roof mold

Drive down just about any main street in Anytown, USA, and you will notice those unsightly dark streaks running down the roofs and siding of houses. You also might notice that those streaks are more than just dark-colored but often include a vast array of greens, browns, yellows, and the like. They extend beyond the roof to encompass the northerly sides of buildings and cling to gutters and window frames. It’s so widespread you could call it an epidemic. If you are experiencing respiratory problems, this seemingly insignificant microorganism could be to blame.

Sliding algae
Figure 1 – family allergies resulting from interior molds and exterior algae infestation after moving in two months earlier (gloeocapsa magma) • victor coppola with greenworks environmental, llc

Primary Colonizer Science

Microorganisms (such as bacteria) are often the primary colonizers of newly created environments. They colonize what initially appear to be inhospitable substrates such as bare rock, glacier surfaces, and even the exterior of the International Space Station

The next microorganism to arrive are the Lichens, organisms formed from a symbiotic relationship between fungi and algae. Well, our roofs and building exteriors could be called inhospitable substrates, and these extremophile bacteria are colonizing them at alarming rates.

Electron microscopic image of lichen
Figure 2- Electron microscopy of post-space flight 08/11/2005 • European Space Agency

Asphalt Shingles

Asphalt shingles are a type of roof shingle that uses asphalt for waterproofing purposes. An American invention first used in 1903, asphalt shingles have been used in roofing projects all over the globe for over a century. It is relatively inexpensive, easy to install, and available in many colors. Making asphalt shingles the go-to roofing material for many homes.

Unfortunately, changes in the asphalt mix are attracting primary colonizing bacteria, the most prevalent being Gloeocapsa magma, which gained notoriety in the Southeast in the 1990s for the dark stained roofs it causes. C. magma has since spread throughout the United States and Canada. It’s probably in your neighborhood, and you didn’t even give it a second thought. But if your family is having odd respiratory issues, you might want to pay closer attention to this cyanobacteria. 

Aged roof shingles
Figure 3- aged asphalt roof shingles with cyanobacteria • gloeocapsa magma

What is Gloeocapsa Magma?

It is a cyanobacteria that originates in fresh water and relies on photosynthesis for energy. As the bacteria drifts from local water sources and starts to colonize your roof, it initially looks like algae in part due to its greenish-blue color.

It can thrive anywhere on your asphalt shingle roof, but it tends to favor north-facing sides of your home that hold moisture a little longer. But it isn’t the only airborne algae or cyanobacteria found. There are dozens and dozens of these microorganisms that have been shown to induce allergens or produce toxins (Genitsaris, 2011).

Gloeocapsa magma
Figure 4 – Microscopy of Gloeocapsa magma

Is It Dangerous?

Gloeocapsa magma is a particularly aggressive fungus that can wreak havoc with your roof as it eats away at the calcium carbonate (CaCO3) in the limestone filler used to weigh your asphalt roof shingles down. It also can join with fungus to create Lichens, tougher organisms than algae alone. All combined, they will be unsightly, reduce the value of your home, and shorten the life expectancy of the roof,  

And while C. magma eats your roof; it will cause the shingles to weaken and start to break down into small dust-like granules. Most experts within the subject area conclude the bacteria to be harmful if left untreated, as the growth holds moisture within shingles, causing premature aging, rotting, and/or granule loss.

As the bacteria goes through its life cycle it too will die and start to breakdown casting off secondary metabolites like Cyanotoxins. When on your home, Cyanotoxins saturate the resulting roof dust much the same way it collects along the shorelines of lakes, ponds and rivers. There it can work its way into the bio-burden of the home or impact occupants entering and exiting the home. 

Redtide 2021-04-15 fl
Figure 5- Red Tide Warning Sign with health concerns • www.floridahealth.gov

Health Effects from Cyanotoxin Exposure

While the research regarding C. magma on your roof is scant, exposure to cyanotoxins has been well-established around algal blooms and red tide. Adverse health effects may range from a mild skin rash to serious illness or, in rare circumstances, death. Acute illnesses caused by short-term exposure to cyanobacteria and cyanotoxins during recreational activities include hay fever-like symptoms, skin rashes, and respiratory and gastrointestinal distress. And yes, your dog is susceptible too.

Cdc cyanobacteria poster
Figure 6- Warning signs for Cyanobacteria from www.cdc.gov/habs/

What Do I Do Now?

There currently is no cure to eradicate roof algae, only better management where roof replacement is the best choice. While the research on the topic regarding the dangers of rooftop fungus, algae, and lichens is scant, experts do agree that fungus should be remediated and water-borne cyanobacteria should be avoided. It’s best to play it safe and get rid of it if you have it. Or reach out to the Indoor Air Quality (IAQ) experts at GreenWorks if you suspect your IAQ has been compromised.

Roof microbials
Figure 7- Mold, lichen, and algae-covered roof; the client doesn’t think this is something to worry about. • Victor Coppola with GreenWorks Environmental, LLC.
Roof streaks
Figure 8 – More typical roof infested with Blue-Green algae, aka Cyanobacteria (Gloeocapsa magma) • Victor Coppola with GreenWorks Environmental, LLC


Asphalt Roofing Manufacturers Association (ARMA). (2017, 05 10). History of Alphalt Roofing and Algae Discoloration of Roofs. Retrieved from Asphalt Roofing: https://www.asphaltroofing.org/algae-discoloration-of-roofs/

Environmental Protection Agency. (2023, 07 13). Health Effects from Cyanotoxins. Retrieved from Cyanobacterial HABs: https://www.epa.gov/cyanohabs/health-effects-cyanotoxins

Environmental Protection Agency. (2023, 07 11). Learn about Cyanobacteria and Cyanotoxins. Retrieved from Cyanobacterial HABs: https://www.epa.gov/cyanohabs/learn-about-cyanobacteria-and-cyanotoxins

European Space Agency. (2005, 08 11). Lichen Survives in Space. Retrieved from European Space Agency Science & Exploration: https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Lichen_survives_in_spaceGenitsaris, S. (2011). Airborne Algae and Cyanobacteria: Occurance and Related Health Effects. Frontiers in Bioscience, 772 – 787.

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Victor Coppola

Victor Coppola is a Building Biologist with decades of diverse environmental experience spanning natural resource management and contaminated sites to Indoor Air Quality (IAQ) and building hygiene matters. He focuses on the three most prevalent issues degrading today's built environment: Moisture Odor & Mold (M.O.M.). Mr. Coppola and his Team are sought out by individuals and professionals concerned about IAQ to those actually suffering from Biotoxin Illness. His hybrid blend of environmental interests and services enable him to give a unique perspective into today's changing environment. Think your home is killing you, better call Victor and his Team at GreenWorks.

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