Unfortunately, this is not a straightforward question as there are so many factors in play that affects the speed of the regrowth of the moss. The likes of lichens take quite some time to grow back so you should not see regrowth for at least a couple of years. However, with moss it depends a lot on the weather in the years following the treatment, the more rainfall we have, the more sun we have then the faster the regrowth. Along with this, environmental factors such as local trees dropping their leaves and even birds dropping moss from other roofs onto yours. With this being said you should see a minimum of 1 year before regrowth and in most cases 2-3 years can pass before you see regrowth. Once you see regrowth we can schedule a maintenance dose to “reset” the clock before the moss takes hold. This can prevent the need for the whole cleaning process to be done again which can be costly.