The Problems

Mosses, lichens and algae are some of the earliest forms of life on this planet, preceding mankind by millions of years. They have remained relatively unchanged during this period of time and range from simple single-celled algae to the somewhat more complex mosses. These growths cause several problems. They are living organisms which only require moisture, light and minute quantities of mineral salts to grow, however, they can grow on virtually any roofing material or surface. Their root systems have the ability to bore into solid granite up to 12mm. Therefore, once established on tiles, they allow the passage of water into the substrate which gives rise to frost attack and shaling of tiles.

These growths excrete acids, mainly oxalic, which attack the alkalinity of materials used, further weakening the tiles and bleaching the colour out. Mosses will grow up under the laps and cause capillary attraction of rain water resulting in roof leaks. When the mosses become large they are dislodged by heavy downpours of rain, resulting in the additional maintenance problem of blocked gutters.

Heavy moss contamination when soaked by rain will considerably increase the weight load on a roof. Once established these colonies lead to the rapid deterioration and breakdown of roofing materials eventually necessitating costly replacement.

Over the last decade the incidence of roof contamination from mosses, lichens and algae has increased at an alarming rate. In 1956 the Clean Air Act was introduced which subsequently reduced the amount of air pollution, and in recent years there has been a general reduction in heavy industries which has given rise to a much cleaner environment. This has resulted in a dramatic increase in the amount of airborne spores. In addition our climate is becoming milder and as a consequence these simple plant forms are able to survive and multiply. Whereas in the past these growths have appeared predominately in rural locations, they have now encroached into inner-city areas and can be seen contaminating some of the most prestigious buildings in the UK.