Thatched roofs are naturally organic structures made from materials like water reed, long straw, or combed wheat reed, which means they hold moisture and can occasionally develop surface mold or algae, particularly in shaded or humid environments. However, a healthy and properly installed thatched roof is designed to shed water efficiently rather than trap stagnant moisture deep within its layers. The exterior surface often weathers to a dark grey or greenish patina due to natural weathering and microscopic biological growth, but this weathering layer does not necessarily mean the roof is rotting internally. Expertly maintained thatch relies on proper pitch and airflow to dry out quickly after rainfall, preventing destructive internal mold and fungal decay.
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