Moss growth on roofs has gradually become more of a problem in many parts of the country today. It causes blocked guttering's, build up behind chimneys, valleys, and gullies, damages the roof coverings, which can reduce the value of your home. Over the last ten/twenty years the incidence of roof contamination from mosses, has increased 
at 
accelerating rates. These problems have become so severe in certain parts of the country that some Local Authorities and Housing Associations have roof cleaning as part of their on going maintenance programmes.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 plant forms are able to survive and multiply. Whereas in the past these growths have appeared mainly in rural locations, they have now spread into inner-city areas and can be seen contaminating some of the most prestigious buildings in the land.
Roofing materials like concrete tiles, slates, fibre, cement and fibre board all become weakened by moss growth to different levels. Even the thinnest layer of moss is a problem because it acts like a sponge, absorbing water, which increases the weight and stress on the roof, shortening its productive life. Frost damage is another problem - by freezing the moss and pushing the tiles/ slates etc up and cracking them or causing leaks. 
Roof cleaning measures such as power washing techniques can remove the moss but will also roughen the surface of the roofing materials, especially concrete materials, reducing the intended life span of the roof. At best is messy and can create more problems than solved, They also spread the moss spores rather than kill them.
There are two different types of metal which when applied, will oxidize and produce a chemical to inhibit moss.Zinc produces zinc carbonate, copper produces copper sulphate. Both products inhibits moss growth. Zinc on a single house would not cause any major problems but if the house next door etc, did the same, this could cause a build up of zinc carbonate which is a known irritant.
Exposure to air and water causes copper to oxidize, creating a fungicide called Copper Sulphate a highly effective moss killer. The effect is obvious where lead flashing's have been installed.
The way we would recommend dealing with the moss problem is to clean the roof off with a and hard brush,to replace any broken tiles,repair any cement work, then to clear the gutters. To apply a moss killer but be aware that some of the chemicals used are harmful to plant life so act accordingly and take the necessary precautions.To attach copper strips along the ridge line.
Remember, we only work on roofs, that is why we are the experts!!
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