Millions of roofs in the United States are plagued with roof moss and roof algae growth. They add to the damage to the roof and help to shorten the life of the roof, they trap water which does accelerate wear and tear. It is easy to clean a roof and more importantly, it is very easy to keep moss and algae from growing again.
People who live in all parts of the nation and have roofs made from all sorts of materials, wood, metal, asphalt, clay or concrete tiles, etc. can have moss and algae accumulate on their roofs. Those places that receive more rainfall and have sustained high levels of humidity have more moss and algae growth as the moss and algae need water to grow and multiply.
Note how the moss typically starts to grow at the top of the vertical slots between shingles. These areas of asphalt shingles are the last place water evaporates from a roof. Once the moss is removed, inspect these slots to ensure the colored ceramic granules are still in place. If the granules are gone and you see just the interior fiberglass mat of the shingle, your roof is well on its way to being replaced.
Controlling Moss on Roofs
Moss formation on roofs is a growing problem. Many homes have cedar shake or shingle roofs, which are more prone to moss growth than asphalt or fiberglass shingle roofs. More people are seeking privacy by hiding their homes among the trees. And in some areas, interest in the resale value of their homes has caused the owners to try to correct years of neglect for their roofs.
Leaves or needles left on the roof from overhanging or nearby trees will retain moisture and cause moss formation. Roofs should be cleaned off periodically, using either a stiff broom or brush, or a high-pressure jet of water. Removing foreign matter from the spaces (keyways) between the individual shingles is especially important, but take care not to damage the shingles. Prune back overhanging tree limbs to allow good air movement and reduce future leaf drop on the roof.
Following are suggestions from Oregon State University to control moss, algae and lichens on roofs:
Scrape away as much moss as possible. A power washer works to remove moss, lichen and algae. Be careful with the tools, as they can damage your roof as well as remove the moss. Keep all organic debris such as leaves and branches off of your roof, deck or patio. Remove branches that overhang your roof and decks to allow direct sunlight and good aeration to reach your roof.
Prevention of Moss Problems
In areas of your roof where you need to control moss, consider first how to prevent moss growth. One option is to install a metal roof. Moss is not able to grow on the smooth surface. If you need a new roof in a moss-prone area, or if you are considering metal roofing for other reasons, this can be a useful and relatively permanent solution. Metal roofing is more expensive than composition shingles, but because metal roofs don't have to be replaced as often, the lifetime cost is comparable.
In western Oregon (and areas with similar climates), cleaning roofs once or twice a year, in the fall and possibly again in the spring, is recommended. Cleaning removes debris (leaves, needles, etc.) that slows drying of the roof and removes moss plants. Wet sweeping will remove most of the moss, as long as plants have not gotten too well established. Getting up on a roof can clearly be dangerous and should not be taken lightly. If your roof slope is steeper than five inches of rise per horizontal foot, you will need either to hire a professional or to use professional equipment.
Biology and Ecology of Mosses
Mosses do not have roots, and so they cant take up water from soil as many other plants do. This means that they need flowing or falling water in order to thrive. In addition, the way mosses reproduce requires flowing water. Mosses cope with this constraint by growing in environments that are wet at least some of the time. Some species also have a remarkable ability to survive desiccation. In dry conditions they are inactive, but quickly recover when water is available.
Roof Treatments to Protect and Add Life to Your Roof
One of the most expensive things you can do in taking care of your home is roof repair or replacement. Most roofers won't tell you, but proper maintenance in the NW saves you thousands of dollars in repair costs.
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How Much Moss Is a Problem?
There is a consensus that growth of moss on most standard residential roofing materials (either three-tab composition shingles or cedar shingles and shakes) can damage the roof. However, there does not appear to be data showing exactly how much moss can be tolerated by a typical homeowner.(4) NCAP recommends that you concentrate your moss control efforts on the parts of the roof most prone to moss problems. These will probably be on north-facing slopes and in the shade of trees or other buildings. Parts of the roof that get direct sun are unlikely to develop moss problems.
MOSS PROBLEMS
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