Mastering Roof Inspections: Asphalt Composition Shingles, Part 43

Biological Growth (continued)

Moss

Moss is a greenish plant. It can grow more thickly than algae. Moss attaches itself to the roof through a shallow root system that can be freed from shingles fairly easily with a brush.

Moss deteriorates shingles by holding moisture against them, but this is a slow process. Moss is mostly a cosmetic issue and, like algae, is a safety issue for those walking the roof.

Lichen

Lichens are composite organisms consisting of a fungus and a photosynthetic partner, such as green or blue-green algae.

Lichens bond tightly to the roof, and when they’re removed from asphalt shingles, they may take granules with them. Damage from lichen removal can resemble blistering.

"Tobacco-Juicing"

"Tobacco-juicing" is the brownish discoloration that appears on the surface of shingles, under certain weather conditions. It’s often temporary and may have a couple of different causes. After especially long periods of intensely sunny days, damp nights and no rain, water-soluble compounds may leach out of asphalt and be deposited on the surface of the shingle. Another way tobacco-juicing appears is when, under those same weather conditions, particulates from air pollution plate out on the shingle surfaces.