Lichen spores are broadcast across roofs with even a light wind, and the spores will grow and develop into mature moss clump formations. In the Northern hemisphere, Moss grows more on the North face of a roof, or in areas with overhanging branches. Shady areas created by branches or other obstructions tend to foster the growth of moss and algae. Morning dew and rainfall will evaporate slower on these surfaces because of the minimal amount of direct sunlight the surfaces receive. Obviously, surfaces that receive more sunlight are less likely to be affected by moss or algae growth.
Moss can be of great concern to the homeowner, and will shorten the life of the roof if left untreated. Just like a household sponge, the shallow root system of thick Moss growth can suck up and store more than four times its weight in water. That is exactly what your moss-laden roof is doing: bearing weight on your sheathing, rafters, etc. In addition, root activity and moisture significantly speed up the deterioration of your shingles.
Fortunately, moss can be a fixable problem if the homeowner doesn’t wait until the roof is too far-gone. Hiring an experienced professional for this dangerous work is an important first step. The proper use of meticulous roof cleaning tools gently removes heavy moss clump formations. The job is very tedious–the roof must be cleaned shingle by shingle, with careful attention paid to all other elements of the roof. This first step in removing the moss should not be over aggressive–typically the total moss removal at this step is 80% to 95%; the remaining 5% to 20% that was too tight or difficult to remove is then treated with an appropriate roof cleaning mixture. What a difference this will make to the look and life of your roof!
What can a Homeowner do to Prevent Moss and Algae Growth?
Preventing or minimizing moss and algae growth on your roof can be as easy as pruning any overhanging branches to decrease the amount of shade on your roof. The additional sunshine will inhibit the growth of moss and algae. In addition, air circulation over the roof will improve, speeding up the drying process after precipitation, and there will be far less organic debris from branches to hold moisture and feed moss and algae growth.