Evaluation of the temperature-reduction effects of moss-based green roofs

• Moss-based green roofs lower maximum indoor temperatures by 2.0–3.5 °C during heatwaves. • Rooftop surface temperatures are reduced by ∼19 °C during peak heat conditions. • Racomitrium japonicum proved viable under full-sun exposure, with supplemental shading offering no thermal advantage. • Field-verified, lightweight (∼4.6 kg/m 2 ) moss roofs are a scalable retrofit solution for urban climate adaptation. To address the persistent lab-reality gap in green roof research, this study empirically evaluated the thermal performance and field viability of a moss-based green roof system installed on an occupied, aging elementary school building in Seoul. Moss panels using Racomitrium japonicum were deployed in two configurations—moss alone (M) and moss with a 95 % shade cloth (M + S)—and compared to a conventional bare concrete roof (control). Under real summer heatwave conditions, the moss roofs reduced maximum indoor temperatures by 2.0–3.5 °C and roof-surface temperatures by approximately 19 °C. These cooling effects were consistently observed both with and without air-conditioning, suggesting potential for reducing building cooling loads. No statistically significant thermal advantage was observed from the shade cloth (p = 0.7152), suggesting that R. japonicum is viable without supplemental shading. Field observations identified bird-induced moss disturbance as a practical implementation issue, which was effectively mitigated using protective mesh. The system’s minimal substrate requirement (2–3 cm) and lightweight profile (∼4.6 kg/m 2 ) establish moss-based green roofs as a scalable, low-impact retrofit strategy for heat mitigation and climate adaptation in dense urban settings. Overall, the findings provide field-based empirical evidence that moss-based green roofs can contribute to mitigating heatwave impacts and enhancing building-level energy efficiency.