Moss grows in moist areas on your roof. Clean your roof once or twice a
year to remove any debris and leaves that can hold moisture. Prune
overhanging branches that provide too much shade to the roof.
Moss can often be removed with a stiff push brush or wire brush.
If you must use chemical cleaners, use the minimum recommended
concentration and redirect roof cleaning water to the sewer system or
vegetated areas where they have time to infiltrate and be broken down in the
soil. Do not reconnect downspouts until the chemical residue cannot be seen
on the roof any longer, or about three rain events. Treat your roof in dry
weather so that the treatment has time to soak into the roof. These
chemicals will only kill the moss, not remove it, so you will have to remove
the moss from your roof to prevent damage. It may be just as easy to remove
the moss without using a chemical treatment.