Most roof stains are caused by the growth of algae,
lichen colonies or moss that feed on organic matter frequently found on roof surfaces. The portions of a roof that receive
the least amount of sunlight are more likely to have roof stains. This explains why some homes may have roof stains only
on one side of the roof, typically the northern and/or western exposure or in heavily shaded areas.
LICHEN COLONIES
Lichens are a
fungus, usually of the class Ascomycetes, that grow symbiotically with algae, resulting in a composite organism that characteristically
forms a crust like or branching growth on shingle granules. Lichens put out root-like tentacles that penetrate deep
into the shingle’s organic, oil base for nourishment, eventually ruining them by creating dark spots, or pock marks
where they grow.
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ALGAE
Algae
is a living organism that thrives on dust, pollen, and the organic materials that make up the roof. Dampness triggers its
growth. Stains are usually more prominent on northern and western exposures and in heavily shaded areas. Algae grows on,
under, and behind the tiny granules that cover the shingles. This results in unsightly stains and streaks on the roof. Heavy
algae on roofs can super heat the attic resulting in higher home cooling costs as well as reducing the natural life span
of the shingles.
MOSS
Thick moss growth with its shallow root system
keeps the roofing materials damp for extended periods of time and this moisture promotes wood rot and can and does
erode the asphalt shingles. Moss typically starts to grow at the top of the vertical slots between the shingles. These areas
of asphalt shingles are the last place water evaporates from a roof. Moss, like lichen colonies, is quite damaging to shingles
and some of the granules underneath the moss may be gone.
