Moss grows in cold, humid environments. If you have moss on your roof, it's probably because the roof is shaded by trees or other structures, allowing moisture to stay and moss to grow. Water and debris increase the chances of moss growing on the roof. Moss will also thrive if the roof is in a shaded area, as shade prevents moisture from evaporating.
Moss tends to form in areas where it is protected from the sun. If there are sections of your roof under heavy tree cover, these are the best places for moss to thrive. And if you live in a humid climate with a lot of rain, you'll most likely notice telltale signs of algae or moss forming on the roof at some point in your home's lifespan. On asphalt or possibly on some (treated) wooden tile roofs, the chemistry of shingles is also involved in the growth or resistance of mosses, lichens and algae.
Some shingle materials contain algaecides or fungicides that also slow the growth of moss on the roof surface. Moss grows in cool, humid environments with plenty of shade. These conditions prevent moisture from evaporating, allowing moss to start growing between the shingles. Sometimes there is so much moss and dirt on a roof that we're not sure what roofing material was used.
If there are trees facing your house, consider pruning the branches that hang over the roof to prevent moss from growing. Trying to remove moss from the ceiling with household cleaning chemicals can cause more harm than good. Even in non-icy climates, the roots or growth structures of moss or lichens eventually penetrate and separate roof tile materials, accelerating their disappearance. Because lichens that grow on the surface of a roof are not as thick as moss, they retain less water on the roof surface and have a lower wear factor than moss.
The oxides that fall through the roof are a pretty good biocide that will slow down the three roof invaders. So what should you do if your roof is covered with moss, lichens, algae, or similar growths? Do you need to replace the roof completely or is there an easy way to safely remove the moss and restore the roof to its previous condition? Keep reading to find out. You can also prevent moss growth by installing zinc or copper cladding strips (such as Amazon's) under the upper ridge on both sides of the roof. Moss that grows on any roof surface will be most intense on sections of the roof that are shaded and exposed to cold and humid weather conditions periodically.
But in general, the roof surface is almost free of moss and the remaining fragments are harmless enough to be left alone. You can see that small dry fragments of dead moss have not come off the roof surface (pictured below to the right) on this fairly low-slope roof. Installing copper or other metal strips along the ridge of an existing roof will slowly remove moss or lichens as rainwater falls on the metal and falls across the roof surface. Debris on the roof after removing the moss can make it harder to see the actual condition of the shingles.
Moss dust is also a highly recommended tool for combating moss because its properties are not harmful to the roof structure. Moss and lichens are more than just a cosmetic problem in many types of roofing materials: asphalt shingles, rolled roofs, wooden shingle roofs, wooden batten roofs.