Algae and moss on architectural shingles are common issues, especially in humid or shaded areas. Algae usually appear as dark streaks or stains running down the roof, caused by airborne spores feeding on the limestone filler in shingles. Moss, on the other hand, is green, fuzzy, and thrives where moisture lingers, often on shaded or poorly draining sections. Both can retain moisture, which may shorten shingle life if left untreated. Simple diagnostics include visually inspecting your roof from the ground with binoculars or safely checking for wet, spongy patches on damp days. If you spot dark streaks or green patches, that’s algae or moss. A gentle cleaning using a mixture of water and mild detergent or a specialized roof cleaner can often remove surface growth. Avoid power washing, as aggressive cleaning can damage shingles and void warranties.
If algae or moss returns quickly or covers a large area, it’s wise to call a professional roofer who can assess underlying issues such as poor ventilation, drainage, or excessive shade. They may suggest treatments with zinc or copper-based solutions that inhibit growth and extend shingle life. When discussing with a contractor, ask if their cleaning method is safe for your specific shingle type and if treatments they apply affect your warranty. Also, inquire about recommendations for improving roof drainage or shade management to prevent regrowth. Taking these steps keeps your shingles both functional and attractive over time without risking damage from improper cleaning.