Moss grows very well in a shady climate also needs moisture or humid environments to thrive. We have plenty of that here in Washington State. The reason they need a wet climate is because moss does not have any roots to save water that it needs to grow.
As moss grows and starts to thicken on a shingle roof it might raise up the shingles allowing for water to go under the shingles. This will cause the sheathing (plywood) to rot and the roof will leak. If high winds come when this has occurred then it will also cause wind damage to the shingles and potentially blow off shingles from the roof. Another cause of moss building up is that moss may damage the shingle and lowers the lifespan of the roof.
*How Not to Remove Moss on a Roof*
Do not pressure wash the moss off of a shingle roof. This will drastically reduce the life of the roof. Pressure washers are high powered and will remove the shingle granules that protect the shingles for their lifespan. Also I have seen it put small holes in the roofing shingles and cause leaks. The same goes for tile roofs or slate roofs. If you pressure wash these roofs to get the moss off then it usually will take the color of the tile with it. Do not use a broom to scrape the moss off of the roof. This too will remove the granules that protect the roof and potentially rip or tear off shingles.
The Best Way to Remove Moss off of a Roof
The best way that I have found for removing moss off of a roof safely is to do it by hand and to use a moss preventative solution to prevent moss in the future. When you do this right, it preserves the life of the shingles and will get rid of the moss. Using a solution after words to prevent moss is a must. Normally apply these on a regular basis to prevent the moss from coming back.
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