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Q I have moss growing on my red tiled roof. Can you tell me if it causes damage to the tiles or the sand and cement rendering? Is it necessary to remove the moss and if so what is the best method?
What steps, if any, can I take to stop the moss reappearing?
DR, by email
A This is a very common situation and absolutely, moss can damage the structural integrity of any type of roof.
Moss basically absorbs moisture from the damp environment. They anchor themselves to a roof with root-like growths called rhizoids. The growth of these rhizoids begins the process of roof degradation. Moss can lift up tiles and, if left untreated, this growth can actually add a substantial weight load to the roof itself.
There are a few ways to get rid of the moss and some are more risky than others. Some people use jet washers, but in my opinion this is too harsh a method. Using high pressure water is likely to create some of its own damage by delaminating tiles and even potentially lifting roof tiles, or dislodging flashing and eroding the pointing of parapet walls and chimneys.
Another option is to try and manually remove the moss with a stiff brush. However, this can also damage the surfaces and does little to stop the moss returning.
In most situations I would advise having an anti-moss treatment spray applied to the roof. This type of application kills moss and lichen and also helps to prevent growth from returning in the near future.
As with anything on a roof, I would recommend you get a professional in to carry out the work due to the potential health and safety issues with working at height. I hope you find this of some help.
Nick Bizley co-founded aspect.co.uk, the London-based maintenance and refurbishment company