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Is your roof covered all over with stains, mosses, algae and lichens?

roof stain causes2

The causes of a dirty roof covering

Most stains on the roof are caused by the growth of algae, lichens colonies or moss. These organisms literally eat your roof. The parts of a roof that receive the least amount of sunlight are more likely to have algae, lichens colonies or moss growth. This explains why some houses only contain stains on one side of the roof, usually the northern and / or western exposure or the extremely shady areas.


An alga is a living organism that thrives best in moist and shady environments. Moisture promotes its growth. Stains are usually more prominent on the northern and western exposure and shady parts of a roof. Algae grow up, under and behind the small grains that cover the roof covering and can house many fungi. This results in ugly stains and stripes on the roof. Roofs with algae and stains absorb heat instead of reflecting it. This results in an overly heated attic and higher fixed loads for your house to cool it as well as a reduction in the natural lifespan of your roofing.


Thick moss growth with a shallow root system keep the roof moist for a long time. This moisture promotes wood rot and causes erosion on roof tiles. Moss usually begins between the roof tiles, growing at the top of the vertical slots. These parts of roof tiles are the last places where the water evaporates from a roof. Moss, just like lichen colonies are quite harmful to roof tiles. Some parts of your roof tiles may even have already disappeared under the moss as a result of this organism.

Lichen colonies

Lichens are a fungus, mostly of the Ascomycetes class within the fungal kingdom, which grow together symbiotic with algae. This results in a composite organism that typically forms a crust-like or branching growth on roof tiles. Lichens expose root-like tentacles that penetrate deeply into the organ of the roof tile for food. Eventually they ruined the roof tiles in the places where they grow by creating dark spots or pits.

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