Polyurethane roof coatings are often chosen for their durability, waterproof properties, and ability to protect underlying roof materials. However, despite their protective qualities, these coatings can still be susceptible to algae and moss growth, especially in damp, shaded, or humid environments. Algae and moss thrive on moisture and organic debris that collects on the roof’s surface, which can happen if the coating wears down, the roof isn’t cleaned regularly, or nearby vegetation drops leaves and debris. This growth can cause discoloration and may hold extra moisture against the surface, potentially leading to faster degradation of the coating and the roof substrate underneath. To diagnose whether algae or moss is present, homeowners can safely perform a visual inspection from the ground or a stable ladder, looking for green streaks or fuzzy patches, particularly in shaded or damp areas of the roof.
If you spot algae or moss, a gentle cleaning with water and a soft brush or a roof cleaning solution designed for polyurethane coatings can often remove the growth without damaging the surface. Avoid harsh chemicals or pressure washing, which can harm the coating or void warranties. However, if the growth is extensive, or if you notice blistering, cracking, or peeling of the coating, it’s best to call a roofing professional who is experienced with polyurethane systems. When consulting a contractor, ask if they use algae-resistant or antimicrobial treatments compatible with polyurethane coatings and how they will ensure their cleaning methods won’t harm your roof. Also, inquire about the product’s warranty conditions regarding algae and moss and what maintenance practices will keep your roof in good shape while preserving that warranty.