Roof cleaning

I'm often asked by my roofing customers if there is any real benefit to removing moss from a roof. Is it something roofing companies have promoted to increase revenue?

Removing roofing moss from roofs has become big business. Home Improvement stores offer a huge variety of products to eradicate Moss and Lichen from your roofing. But does roof growth actually harm the roof?

The Problem

There are thousands of different types of lichen, but the one most commonly found on roofing is Ascomycetes Foliose. Fungus and bacteria combine to make a symbiotic association. This leads to the yellow green coral like growth found on roof coverings. It is very hardy and will survive long periods of extreme weather.

As part of the lichens growth cycle it burrows into the roof surface. The root system bonds to the roof covering. It is this action which causes the damage to the roofing. The lichen bonds to the surface of paintwork eventually causing it to flake and blister. On metal tiled roofing the chipped protective coating is often completely removed exposing the tile to rust.

On concrete tile roofing moss will block the interlocking part of the tile. This can cause the channels to leak, overflowing water into the living space. In areas subject to frequent frosts the roof damage is worse. Water inside the moss expands on freezing. This can cause damage to the surface of the roof tile. Tiles become pitted and cracked. Furthermore, the roofing is never allowed to dry out. The moss keeps the roof surface constantly damp which speeds up deterioration and eventually makes the tiles more porous.

The solution

Removal of moss can be achieved in a number of ways. If the moss or Lichen has taken a firm grip of the roof surface, mechanical removal with a brush is not recommended. The moss/Lichen must be killed off first before it is removed. If you try to remove it before the root system is dead, it may further damage the roofing. Moss killers are usually made up of a solution high in Sodium Hypochlorite. Household bleach is not strong enough to kill lichen but it may be effective with light moss growth. Commercial moss killers are 5 times the strength of domestic bleach and will knock both Lichen and moss down. If you are going to do the job yourself try to do it in a dry spell. The growth will naturally soak in more mixture if it is dry. Use a soft brush to work the mixture into high growth areas.

Take care when using these products and always follow the manufacturer's instructions. It's a good idea to remove the down pipe from the spouting before you start. That way you can safely collect the waste and dispose of safely.

A gentler more permanent solution to removing roof moss is to use copper strips on the ridge of the roofing. These provide a gentle fungicidal wash over the roof when it rains and stops the moss from growing. Copper strips may only be used on non metallic roof coverings due to galvanic corrosion. The copper run off will corrode any metal surface it comes into contact with including spouting.

The Benefit

To extend the life of your roofing it really is important to prevent damage from roof Moss and Lichen. Any money spent on roof cleaning will easily be recouped by the prolonged life of your roof covering. It will also save you considerable time clearing your gutters and spouting. Furthermore, a clean roof also shows potential buyers that the property has been well maintained.