Regular maintenance is crucial to prolong the lifespan of a roof and preserve its integrity. This should include inspection for broken and loose tiles, checking gutters and downpipes, and the removal of any organic material that may have built up, such as leaves, moss and lichen.
Moss and lichen tends to flourish on roofs in rural areas, where trees are nearby and where there are shady, damp conditions. It also benefits from a slightly acidic environment (pH 5.0 to 5.5). Steeper pitched roofs are less likely to support moss and lichen growth as they shed water more quickly than roofs with a low pitch. In contrast, north-facing and shallow roofs tend to remain damper for longer and will therefore attract mosses and lichens.
In normal circumstances, a small amount of growth is not harmful to the actual roof tiles or slates. However, in extreme cases, it may affect the flow of water down the roof, hampering drainage, or may retain water that may increase the risk of damage or leaks developing. In these cases, moss and lichen should be removed to avoid possible water ingress into the roof space.
There are several methods for the removal of moss and lichen:
Spraying moss with a toxic wash
As moss grows in slightly acidic conditions, use a moss killer or alkali solution to wash the roof, although care must be taken not to contaminate ground water. It is not recommended to remove moss by pressure washing as this can force water into the roof space, particularly if sprayed upward from ground level.
Fitting copper to inhibit moss growth on the roof
Copper wire can be fitted across the roof at intervals using nails or screws on the side of the roof. Copper ridges can also be fitted across the roof ridge line. As rainwater passes over the copper, a reaction takes place. The water that runs down the roof will leave a residue that inhibits moss growth.
Scraping moss off the roof
Moss can be scraped off by hand but this must be performed with caution to avoid damaging roof tiles, particularly in the case of timber or asphalt shingles
Before proceeding with any remedial work to remove moss or lichen, we would recommend speaking to a roofing maintenance professional. If unsure, you should contact the Marley Eternit technical department for further details.