Moss on the Roof

May 17 2018 0comment

Moss on the Roof

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Barrier for Flat RoofMost roofs tend to experience moss or lichen growth which can develop into a problem if it spreads to more than just a few patches here and there.  Moss absorbs moisture like a sponge and can result in the roof being constantly wet.  If the moisture gets under the roof membrane or tiles, the wooden components of the roof may begin to rot, threatening the structural integrity of the whole roof and necessitating expensive repair or replacement work.   This is an equal opportunity problem that affects roofs of all types, pitched ad flat.

Heavy moss growth can negatively affect the drainage, even on a pitched roof as it obstructs the path of the water by absorbing it instead of letting it drain away.  Moss may be beautiful close up, but just take a look at the way it’s grabbing the water droplets in this photo!  Moss on the roof may also attract wildlife – insects and birds in particular.  Birds often break up moss and dislodge pieces that may then drop into gutters and downpipes, potentially causing a blockage.  

In order to avoid expensive roof repairs, moss should be removed from the roof as soon as possible, especially if it covers large areas.  Pressure washing the roof, although tempting may cause damage to the roof, so should be avoided.  However, there are methods that can be used to remove moss and discourage it from growing back.


  • Small patches of moss can be brushed away with a stiff but be careful when accessing the roof and use the correct type of access equipment.
  • Applying moss killer may be effective, but the chemicals in it may contaminate groundwater.  Always use protective clothing when using chemicals of this type.
  • A specialist roofing professional will remove the moss with a minimised risk of damaging your roof whilst doing so.


  • Installing copper ridges to the roof will prevent the growth of moss – when rainwater falls on the copper ridges, a copper residue is released and runs down the roof discouraging the growth of moss.
  • Regular cleaning and maintenance can keep your roof in good condition and prevent the growth of moss.

Whichever methods you choose to eliminate and prevent moss on the roof, accessing the roof always carries risks.  This is just as true of flat roofs as it is of sloping roofs.  The right access Post and Chain Barrierequipment should always be used when venturing onto a roof.  A flat roof may look safe to walk on, but could be fragile in places, exacerbating the risks involved with moss removal on a flat roof.  Anybody who needs regular access to a flat roof, for moss removal or any other type of maintenance should consider taking advantage of a safe roof walker system that will allow access to certain parts of the roof in a safe manner.  If the flat roof is on a commercial building, the duty holder has an obligation to provide safe access for personnel who are expected to work on the roof – this should include edge protection such as a roof barrier system.

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