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Exceeding the minimum in Home Inspections
Roofing: Lichens: Are plant forms comprising of fungus and algae growing symbiotically. Lichen’s root-like structures [rhiznes] grow downward into the granules. These cause damage when they die and fall away, taking granules with them. Algae: are dark-colored and can grow generally across expansive areas on slopes or as small defined spots. Algae does not harm shingles. Algae flourish with moisture and are found regularly on north slopes or where the roof is shaded by tree branches. Moss: Moss growing on any roof surface will be more severe on roof sections that area shaded and exposed to periodically damp cool weather conditions. Moss and lichens are more than a cosmetic issue on many kinds of roofing materials - asphalt shingles, roll roofing, wood shingle roofs, wood shake roofs. By holding moisture against the roof surface lichens but more so moss speed the wear of the asphalt shingle surface in freezing climates by increasing frost damage to the mineral granule coating on the shingles. Some images of Lichens, Algae and Moss “Scrubbing” a roof is NOT recommended (brushing, power washing) as this can and usually does remove the protective aggregates. There are cleaning solutions available and should be discussed with a professional contractor that is familiar with such.  
Paul’s Home Inspection LHI #10813 / Ph: 318-820-1187