Advantage Roof Cleaning wrote:

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When I was first learning roof cleaning, I was informed the algae actually eats the limestone additive found in asphalt shingles. Does anyone have documentation substantiating this?

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 It doesn't exactly eat the limestone, here is what happens. The water from the limestone is at a good PH to help "feed" or fertilize the algae.

The way that algae harms a roof is this, it wraps itself around the base of the granules, and as as it thickens, it pushes the granules, and can cause them to fall off.

Green Apple Roof Cleaners LLC wrote:

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Can the Algae ever get under the shingles and into the sheeting ?

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 In really bad cases, yes! 

Advantage Roof Cleaning wrote:

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Thanks Chris for clarifying. 

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 Now Lichens are another story! 

Here is an opinion from some roof inspectors about if Algae eats roofs, or not.

Algae, Fungus, and Lichen Damage

Does Algae, Fungus, or Lichen damage a roof? Algae, fungus, and lichen on a roof is unsightly, and up until now, were believed to have no long term effects on an asphalt roofs. Recent studies have shown fungus, algae, and lichen may affect the overall performance of an asphalt shingle. The fungus and lichen require an organic based food source to survive. The asphalt in the shingle provides the nourishment for the fungus and lichen to flourish. The fungus and lichen can grow at a rapid rate, completely covering a roof slope in some cases. The fungus secretes enzymes into the asphalt which begin to digest the material at the base of the granule surface. The lichen has small roots that embed down underneath the granule surface to provide nourishment for the infestation. As the lichen blooms die, they pull away the granule surface which exposes small areas of asphalt. The open areas of asphalt are RESTRICTED to the area of lichen growth only. The algae requires an inorganic material to feed upon. Shingle manufacturers sometimes incorporate limestone (dolomite) into the manufacturing process, a specific food source for the algae. Algae are the least harmful of these three infestations.