Fiberglass shingles are a popular roofing material due to their durability and affordability, but they can be prone to algae and moss growth, especially in humid or shaded environments. Algae appears as dark streaks or blotches, often black or greenish, while moss looks like fuzzy green patches. These growths occur because moisture gets trapped on the shingle surface, providing ideal conditions for spores to thrive. This is particularly common on north-facing roofs or areas shaded by trees, where sunlight struggles to dry the moisture quickly. Algae and moss not only affect the aesthetic of your roof but can also degrade shingles over time, potentially leading to premature aging or roof leaks if left untreated.
To diagnose algae or moss, a simple visual inspection from the ground or a safe ladder check can confirm suspicious dark streaks or green patches on your fiberglass shingles. You can perform a gentle rinse with water or scrub lightly using a soft brush and a mixture of water and mild bleach (one part bleach to four parts water), but avoid harsh chemicals or power washing that could damage the shingles. If you notice persistent growth or signs of shingle damage, it's time to call a professional roofer. When consulting a contractor, ask if their treatment methods are safe for your shingles and ask about preventive measures, like zinc or copper nail strips, which can help inhibit future growth without voiding your warranty. Ensuring the roofer uses appropriate techniques and products will help maintain your roof’s integrity and appearance.