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.
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.
