Roof stains caused by algae, lichen colonies or moss feed on the organic limestone commonly found on roof surfaces. Roof tops that are shaded are more likely to have roof stains, the reason for this is the shaded areas stay moist and supply a water source to these organisms.
Lichens are a fungus, that are related to algae, resulting in a composite organism that forms a crust like growth on limestone shingle granules. Lichens put out root-like tentacles that penetrate into the shingle’s limestone base for nourishment, eventually ruining them by creating pock marks where they grow.
An algae known as Gloeocapsa Magma is the culprit and thisblack algae. It affects nearly 80 percent of the homes across the United States. Gloeocapsa Magma is a species of algae that causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments. A preferred food source of this algae is limestone which is used as “filler material” by most shingle manufactures.
Moss growing on any roof surface will be more severe on roof sections that area shaded and exposed to periodically damp cool weather conditions.
The absence of sunlight on a roof surface is often the determining factor in the amount of moss. When shade and cool moist conditions combine, moss or
growth on a roof surface is more likely.
Thick moss growth with its shallow root system keeps the roofing materials damp for extended periods of time and this moisture promotes the wood to rot.