I have been asked to clean an old peoples home tiled roof. After looking into it, as this will be the first time we have done this, i can find a detergent based cleaner to clean the roof, (which is majorly covererd in moss) but is there a sealer or something to stop the moss growing back? As there is a company that says they spray some solution on the roof to stop it, but i thought you could never stop moss growing on anything? Any help and advice would be greatly appreciated.