Moss, left unchecked, can grow…like a weed. It reproduces through spores which will, moved by the wind, land on additional areas of the roof.
Mosses belong to a group of plants known as the BRYOPHYTES. Bryophytes have no roots, but they do have thin (one cell thick!) root-like structures which serve for attachment and water absorption. (via UCSB Scienceline).
These root-like structures anchor to the roof surface. Over time, if moss is left to grow, they will get under roof shingles and tiles. As the it grows, it can crack and pull apart shingles creating an opportunity for water to get underneath.
Moss soaks up and stores water like a sponge. Some of that can make its way back under the shingles through capillary action.
With asphalt singles, the moss, being anchored to them, will damage the UV and protective layer of granules. Waiting too long to clean off moss now means the shingles are more likely to crack and break in the sun further increasing the chance of water ingress (and contributing to the shorter lifespan of your roof, potentially even voiding your warranty!
Increased growth of moss can result in higher electric bills too. Under the right conditions like here in the Pacific Northwest, moss can become quite thick. Covering a large enough area of a roof, it can act like insulation increasing the temperature in the attic or crawl space, and the overall interior space. In fact, moss has been used as insulation!
If you have moss growing on your roof, have it professionally cleaned sooner than later.
Make the necessary repairs
One reason for hiring a professional – they will be able to assess the condition of your roof after it has been cleaned. Catching damage now provides a chance to fix it before repairs become costlier.
Replace damaged shingles, flashing, make sure gutters are cleaned and properly secured, and look for any other signs of trouble.
Keeping your roof moss-free
The best solution to a problem is often preventing it in the first place. While moss cannot be completely prevented, there are some ways to limit new growth. Its starts with routine inspections and maintenance:
Moss thrives in damp conditions. Leaking downspouts and clogged gutters provide a perfect environment for growth. Make sure they are free of debris and flowing properly. Inspecting them twice per year is recommended.
Moss on a roof is more than a cosmetic issue. If not cleaned properly, it could lead to damage, costly repairs, and/or replacing your roof long before it would normally be required.
Have your roof cleaned professionally, repairs made as needed, do some preventive, routine maintenance to prevent or limit future growth, and have regular inspections done to get the most life out of your roof.