Modified bitumen roofs are a popular choice for flat or low-slope roofs, known for their durability and waterproof qualities. However, like many roofing materials, they can develop algae and moss growth over time, especially in humid or shaded areas where moisture tends to linger. Algae appear as dark streaks or patches, while moss looks like small, soft green clumps. These growths can trap moisture against the roofing surface, which may eventually lead to premature wear or leaks if left unchecked. Simple diagnostics involve a close visual inspection after a rain or dew, looking for persistent damp spots or discoloration that doesn't dry quickly. A safe DIY check includes gently wiping the area with a damp cloth to see if the green or black staining comes off easily, indicating surface growth rather than deeper damage.
For small algae or moss patches on a modified bitumen roof, homeowners can try a gentle cleaning method using a mixture of water and mild soap or a specialized roof cleaner that’s safe for bitumen, avoiding harsh chemicals that could damage the membrane. It’s important not to pressure wash or scrub aggressively, as this might harm the roof’s protective layers. If moss or algae growth returns quickly or covers a large area, it’s a good idea to call a professional roofer who can assess underlying problems like poor drainage, shading, or roof aging. When consulting a contractor, ask how their cleaning methods protect the bitumen membrane and whether they offer treatments to prevent regrowth without voiding your roof’s warranty. Another helpful question is how often they recommend inspections or cleanings to keep your roof in optimal condition long-term.