The danger in letting it grow unchecked

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.