01 Feb 2018
Roof Pathogens Explained - Featured Image

In Traverse City, like most cities, there are numerous historic homes, and you’ll often see the roofs of these homes with moss and lichen growing on them. Although some people may find this aesthetically pleasing there is a high probability it is causing damage to your roof. Both debris from overhanging trees as well as the organic materials found in shingles and cedar shakes can feed the growth of moss and lichen.


Lichen is a combination of algae and fungus and usually has a light, mint-green color. It doesn’t trap as much water against the surface of the roof as moss, but it can be acidic and has strands that can penetrate into the shingles and cedar shakes.

Moss and lichen commonly grow in areas that are both damp and shaded. Sunlight dries out algae and fungus and usually causes its death. There are a couple of different neighborhoods in Traverse City that are encased by large mature trees. These trees are beautiful, yes, but they help aid the growth of algae and fungus by providing shade and debris that feed these roof pathogens.

Moss absorbs and holds onto moisture, and with a combination of moisture, organic materials in the shingle and shade, pathogens grow. One issue with both moss and lichen is that the roots can grow under and even into the shingles, effectively destroying them.

How to Treat Moss

You can simply remove the fungal growth from your roof with a garden hose and pair of gloves. Simply hose the growth down, and remove it with your hands. Note that a power washer might not be the best choice. The water pressure might be too much for your shingles to handle and could incidentally cause damage.

You can also bleach growth away. Bleach will kill the growth, but make sure to use it with care. Bleach can cause discoloration of your shingles. Be sure to dilute the bleach with a little water first.
In addition to bleach, there are a number of different chemicals out there that are specially formulated to kill the growth of algae/fungus, without having the damaging effects to your roof.

How to Prevent Roof Pathogens

  • Trim tree branches back from roof areas of your home. This will limit the amount of shade on your roof and debris falling from the tree.
  • Keep your roof and gutters free of leaves, sticks, and other sorts of debris.
  • For existing “non-Algae resistant” roofs Zinc strips can be added. Both zinc and copper serve as a fungicide/algaecide and can be installed on the upper portion of the roof 2’ below the ridge line. When it rains, zinc is released onto the roof killing and preventing algae and fungus growth.
  • Finally, the best measures are always preventative. Most quality shingles currently on the market are algae resistant. Manufacturers have managed to embed copper and zinc into the granules rendering the entire shingle “algae resistant” for up to 20+ years. These products have been on the market for over two decades now and have proven to be very effective. Of course, always check to make sure your contractor is including “AR” shingles on their bid, never assume!

Final Thoughts

Although they may seem harmless, moss and lichen are in fact roof pathogens and can take a toll on your roof if left untreated. Keep in mind that it’s easier to remove newer growth than well established growth. If your roof is covered with algae and fungus growth, contact the roofing professionals here at Northshore Exteriors to receive a free inspection and estimate for remediation or replacement.