We all have seen roof surfaces where moss, algae or lichen has begun to grow or collect on the surface. Often times people make the assumption that a noticeable buildup of moss or lichen is an indication that the roof  needs to be replaced. This is not necessarily the case, but it should not be ignored.

First, you should understand that moss, algae and lichen tend to collect on roof surfaces that are heavily shaded and/or are regularly damp or wet. The buildup of moss occurs very slowly over a long period of time. As a result, it is somewhat rare to see significant moss buildup on a roof that is very young in age.

Over the long term, a buildup of moss can be detrimental. The moss traps moisture, eventually causing accelerated wear, especially in cold climates. For this reason we typically advise homeowners to take steps to clean a roof that has a buildup of moss and/or lichen.

Steps can also be taken to help prevent the eventual of buildup of moss, lichens, and algae. Roofing contractors can install metal strips at the peak of the roof. The metal is usually zinc, but galvanized metal and copper are also used. Minerals and ions that wash off the metals when it rains will retard the growth of moss or algae on the shingles. Installing metal strips along the ridge of a roof that already has some moss or lichen buildup can also be beneficial. It will help to kill lichen and moss when rainwater gradually washes over the roof system.

Care must be taken when trying to clean roofs that have a buildup of moss, lichen or algae. Gentle cleaning with a soft brush can be beneficial. It is important to not aggressively scrub the roof since it can damage the shingles. Of course, if the roof shingles are already worn, dried, cracked and brittle they are probably beyond saving, and roof replacement becomes more imminent. There are also roofing contractors who can be hired to clean a roof. You should consult with a number of contractors so that an educated opinion can be made as to whether the cost is justified, and whether the methods used are truly beneficial. The contractor that you choose should be able to provide you with references so that you can consult with satisfied customers.