Updated: Feb 17, 2020
According to Britannica, there are at least 12,000 species of moss. Moss does great things for the forest including helping to keep the soil wet, slowing down erosion, and breaking
stuff down to release nutrients that other plants can use. Some people use peat moss for gardening since it holds water nicely. Moss may be beneficial in nature but it can wreak havoc on your roof.
As moss grows, it tends to work its way between the shingles, lifting the shingles up which can damage the seal between the shingles and make it easy for the wind to catch them. Moss can also re-direct and/or slow down water flow forcing it under the shingles and making your roof leak.
When it comes to moss, prevention is the most important thing. Trimming or removing trees that cast shade on the house and keeping the roof clean using a leaf blower is the best way to minimize or eliminate moss growth. One option that some people use is to install zinc or copper strips at the hips and/or ridges. I don't personally recommend this method. I have seen roofs where zinc strips were installed and they didn't seem to help prevent moss at all. Zinc strips also have a way of coming unfastened, probably because the nails that are specially made for them are typically too short.
Many shingles come with copper in the shingles. They are referred to as "AR" (algae resistant). These shingles are pretty good at stopping black algae streaks from forming on the roof but are not very good at preventing moss growth.
If you can't or don't want to keep your roof out of the shade or you still have some moss growth without shade, there is the option of treating your roof to kill the moss. It is important to kill the moss before it gets bad enough to cause significant damage. You should have your roof treated when you see the first sign of moss.
There are many ways that people have alleged will work for killing moss. Be very careful if you decide to apply one of these treatments or do anything on your roof yourself. Not only is there the chance of getting hurt, you could also damage your roofing. One method is to increase or decrease the acidity to a point that kills the moss. Applying vinegar or even lemon juice is supposed to do the trick. Others claim dish soap does the trick. Acidic substances such as vinegar or products containing detergents such as modern dish soap can cause damage to the shingles effectively making it pointless to remove or kill the moss. The method that we use is to apply zinc sulfate powder.
You may be wondering, what if the moss is already bad or I just want my roof to look really clean? Can I pressure wash my roof or sweep it off? The answer is no. I don't recommend pressure washing or sweeping the roof since it can easily wash away the granules that protect the rest of the shingle from sun damage. Pressure washing can take years of life from your roofing. If you decide to clean your roof, try low pressure washing with a garden hose first to reduce the risk to your roofing. If you have fairly significant moss growth on your roof, be sure that it is cleaned as gently as possible and be aware that it could damage or destroy your shingles.