In general, roofs should be cleaned annually as a matter of preventative maintenance, including a moss treatment.  However, as a roof ages more frequent cleanings may be necessary.

Gerard’s recommended moss treatment, MossBoss, works to kill existing growth along with their spores that may remain dormant for up to two years before forming visible growths.

A new Gerard roof typically requires no moss/algae cleaning for the first five years and then should be treated annually with a moss treatment.