A roof exposed to the elements can accumulate a buildup of dirt, algae and moss, weakening its ability to protect the interior of your home. Debris not removed from the roof eventually will end up in the gutters, causing clogs and overflowing. A regular roof cleaning can extend the lifespan of your roofing system.
Organisms like algae, moss and lichen stain the roof and detract from curb appeal. Especially if your roofing tiles are made of wood, while some moss growth is benign, other plant forms see shingles as food. If left untreated, they can harm your roof by eating through tiles until part or all of the roof needs to be replaced.
Even when plant growth is benign, it still can have adverse effects. Moss (and other types of plant life) covering an entire roof limits its ability to reflect the sun. Instead, the moss will absorb the heat, making it harder to keep the interior cool. Moss acts like a sponge, retaining a lot of moisture. Not only does it add weight, but moss growth also affects surface tension and loosens roofing granules (which might be washed down into the gutters).
How often should you plan to clean your roof or have it cleaned for you? A combination of factors contributes to organism growth, including the amount of moisture; how much of your roof is shaded; and the number of trees growing nearby. If your home is situated on a north-facing property with lots of trees, plan on cleaning the roof (first) seasonally along with your gutters, once in the spring, then again in the fall. Should this be too labour-intensive or not in your budget, schedule it to be done at least once a year.