Problems with lichen

Where and when the air that we breathe is highly polluted, moss and lichen struggle to survive, but where the air is clean they will survive, accordingly as the clean air act takes effect the problem of lichen on roof materials is increasing.

There is no issue with the erosion itself on a building, but the acidic releases will affect all natural and manmade roofing products including bituminous sheets, metals, lead in particular, and are known to damage the galvanisation of steel components.

Left untreated, lichen can cause damage to the colour pigmentation and resin coating to bituminous sheets causing degradation to the sheet structure, particularly in cases when moss is also allowed to build up in the corrugation bases which results in the high moisture content at this point and as a result softens and degrades the sheet structure and can reduce the service life of the roof covering, any moss on the roof should should be removed with a stiff bristled brush and the area treated as required.

Restoration of damaged surfaces

Problems with moss

Moss is a very simple plant form which does not have roots or means to collect or move water around inside its form. It therefore has to absorb the moisture directly from the roof surface, this is why it thrives in damp shady places, such as under tree cover or in gutters.

As moss requires collected nutrients draining down the roof sheet in rainwater to exist, it is associated with wet conditions on north facing roofs, or shaded roofs under overhanging trees providing moist leaf mould on which moss thrives.

Generally whilst you find lichen growing on the exposed surfaces of roofs moss prefers damp sheltered areas. Gradually Moss feeding on nutrients present in the water draining down the roof will grow and in effect build a ‘dam’ in the sheet corrugations in order to retain more moisture.

Problems with mould

Mould is ever-present in the environment it is spread by tiny spores which float in the air. It can establish and grow on almost any receptive surface that spores land and find moisture allied to a constant temperature, between 40 and 100 degrees F.
In theory this includes about every place in a domestic situation that a damp environment is maintained from shower rooms to damp fabrics left in a badly ventilated position.

You can easily spot the most visible type of mould called mildew, which begins as a grey coating, this forms into black spots which in turn grow to form larger colonies. This is normally the fungus you notice in grout lines in a badly maintained shower, or on damp walls, and outdoors on the surfaces such as decking and timber particularly if situated in damp and shady areas.

Caring for Onduline Roof Sheets

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