Science Behind the slime

The granules on your shingles are very important. They not only protect the asphalt, they are designed to reflect heat. Since the growth is black and covers the granules, it absorbs much more heat, which not only heats up your house (That’s right. Hello higher electric bill!), but breaks down the asphalt even more. This causes the shingles to become dry and brittle. Read more to learn about what exactly is ruining your roof.


That unpleasant-looking algae that grows on your roof has a very fittingly unpleasant name — Gloeocapsa magma. Gloeocapsa magma is an airborne algae with a taste for limestone, a common component of asphalt roof shingles. The result of this strange appetite is ugly black streaks that can build up and completely discolor a roof in just a few years.

How does Gloeocapsa end up on your roof? Commonly, reproductive spores are blown there by the wind, birds, squirrels, and other small animals also act as spore carriers. Algae prosper where nutrients, moisture, and heat are present, and a sun-warmed, rain-dampened asphalt roof is a perfect host environment. Additionally, the porous limestone on shingles absorbs moisture, boosting growth. Once a colony establishes itself, the algae form a dark covering to protect it from the sun’s ultraviolet rays, creating the black streaks that appear on your roof. These streaks are multiple layers of dead algae cells that build up over time.

Many people believe Gloeocapsa to be only an optic issue, but prolonged contamination can affect a roof’s service life. The limestone granules are on your shingles for a reason. They provide a protective barrier atop the shingles. As the algae eat away at the limestone, this barrier diminishes, resulting in premature shingle failure. Gloeocapsa also absorbs heat, causing roof surface temperatures to rise. The result is a hotter home, which means a greater load on the air-conditioning system.

The fungi on roofs lack chlorophyll. They are unable to manufacture food from raw materials, so they must obtain nutrition from some form of organic matter. This means that like algae, they need a warm, humid environment to thrive.

Another thing that fungi has in common with algae is that it, too consumes asphalt. It also consumes the ceramic granules that protect against damaging UV radiation and insulate the roof against extreme heat (another reason the roof overheats).

Not all mold (fungi) and algae pose a danger to health. However, some do, especially for those who suffer from allergies, asthma, and respiratory problems. Fungi and algae spores can get inside your home because they end up on driveways and sidewalks from rain, and are easily tracked indoors. They can even be drawn into your air conditioning systems and populate the ducts.

Different mold species can have different effects, but it is very important to remember that any excessive mold growth should be taken care of.


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