I have moss all over my roof, how do I remove it?

Here’s the low down on the growth of moss and lichens on your roof
 
Why does moss grow on tiled roofs?
The main reason moss is able to grow on roofs is that the surface of roof tiles filter out dirt from rainwater over time. This can be aggravated by dead leaves blowing onto the roof, becoming lodged and then decaying. Spores and seeds of mosses, weeds and lichens can then be blown on top of these elements and sooner or later they begin to grow.
 
Which roofs are most affected by moss?
Naturally, the roofs most susceptible to moss and lichen growth are those near to trees and vegetation – and parts of the roof that are shady or damp will be particularly affected. Steeper pitched roofs are less likely to spark moss and lichen growth, as they shed water more quickly and gather less dirt from the rainwater. North facing slopes that remain damper for longer may experience moss and lichen growth more than others.
 
What are the effects of moss growth?
There is every chance moss growth has little or no impact on the function of your roof, although it can slow the flow of water to gutters, which means water is held against tiles for a much longer period of time. If the moss or lichens affect the drainage of water down valleys and guttering, they should be removed. However, a lot of the time harmless moss growth can provide an elegant touch of character and is even sought after by some homeowners.
 
Removing moss
Method one: Toxic wash
Although a relatively cheap method of removing moss, as the name suggests, undertaking a toxic wash requires great care to be taken. It’s a job best suited to professionals with a proprietary toxic chemical in order to avoid the potential risks. Any wash that is toxic to moss will also be toxic to garden plants in the vicinity of the roof and potentially those in your neighbours’ gardens. It can also be potentially hazardous to birds and wildlife – so make sure you’re aware of the risks before getting started.
 
It takes a few days for a toxic wash to take effect, and it’s best to apply the wash in dry weather if possible (rain can wash the chemicals off before they have had time to act). You can speed up the process by removing thick patches of moss before the wash is undertaken.
 
One treatment is usually sufficient, but in rare cases it may need to be repeated the wash process. The dead growths will weather off and disappear quite quickly. Some contractors will recommend using a pressure washer to washing moss off. Even if you ensure the spray is only aimed down the roof, to reduce water penetration into the roof space, this is not advisable due to the damage that could be caused.
Some washes leave a residue that stops subsequent growth, but even in the best circumstances this will only last two or three years.
 
There are Environmental and Health & Safety regulations relating to the removal of moss using toxic washes, so be careful to check the Building Research Establishment (BRE) Digest 139, “Control of lichens, moss and similar growths” or make sure the professionals you hire already have.
 
Method two: Copper Wire
A more permanent way to avoid moss and lichen growth on your roof is to trail copper wires across the roof surface. These can be fixed at intervals across the entire roof, or just affected areas, below the front edge of the tiles. They work because with every rainfall, the copper slowly oxidises in the atmosphere and provides the roof with a thin layer of copper salt which prevents renewed moss growth. The Copper Development Association can provide full details on how it works – contact them on mail@copperdev.co.uk or visit www.cda.org
 
Method three: Scraping
This is exactly what it sounds like – scraping moss from the roof. This method is never recommended as it usually results in damaged roof tiles and can leave permanent, ugly scrape marks on the roof. It also offers no form of long term prevention whatsoever.
 
Things to remember
-       Generally, moss and lichen growth is not unsightly and in many cases adds character to a roof.
-        If moss is affecting the discharge of water from the roof, it needs to be addressed.
-        Removal is best undertaken by toxic chemical wash. Garden centres do sell washes, however it advisable to take professional advice.
-        Copper wire can prevent moss and lichen growth, but does not work in all cases.