It has been done on the continent for many years. The technique consists in using a quaternary ammonium biocide to kill the "bio layer", that is all live organisms on the roof. Quaternary ammoniums are powerful algaecides, and deplete moss and lichen from their embedded algae. As they rely on the algae for food, they simply die. The dark discolourations sometimes mistaken for sout deposits are in fact micro-organisms dwelling at the surface of most concrete tiles. The micro-organisms will also die and gradually wash away, revealing the original colour of the roof.
The chemical then breaks down into residues eaten by ground bacteria. The environmental footprint is limited to the roof. The downside of the mechanism is that after the breaking down no latent effect can be expected. A normal roof needs one cleaning every 8 to 10 years only. If it is under shadow, or - worse - under trees the growth will come back faster particularly on a porous tile. No chemical will solve the problem. It is a design issue.
The key to success is to apply the right concentration and the right amount. Concentrations recommended for cleaning a driveway or a patio are often too weak for a roof. The tiles should be drenched to saturation, and the moss balls soaked through and through. The right product can be sourced on internet, preferably from a company showing a degree of experience in this specialised field.
The cost of cleaning a roof the non aggressive way is significantly less than using wire brushes or jet cleaning. Typically one third. Some companies will do it, but the technique is available to a private individuals as well. The ideal solution is to hire the specialised equipment : A chemical injection box and a light weight boom is often sufficient to carry out the spraying from the ground.
The chemical then breaks down into residues eaten by ground bacteria. The environmental footprint is limited to the roof. The downside of the mechanism is that after the breaking down no latent effect can be expected. A normal roof needs one cleaning every 8 to 10 years only. If it is under shadow, or - worse - under trees the growth will come back faster particularly on a porous tile. No chemical will solve the problem. It is a design issue.
The key to success is to apply the right concentration and the right amount. Concentrations recommended for cleaning a driveway or a patio are often too weak for a roof. The tiles should be drenched to saturation, and the moss balls soaked through and through. The right product can be sourced on internet, preferably from a company showing a degree of experience in this specialised field.
The cost of cleaning a roof the non aggressive way is significantly less than using wire brushes or jet cleaning. Typically one third. Some companies will do it, but the technique is available to a private individuals as well. The ideal solution is to hire the specialised equipment : A chemical injection box and a light weight boom is often sufficient to carry out the spraying from the ground.
