Assessment of terrace gardens as modifiers of building microclimate

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Hard concrete roofs cause excessive heat gain impacting thermal comfort in buildings. Terrace gardens promoting greening at higher levels of built structures are seen as one of the key mitigating strategies for modifying building microclimate and improving urban health. We have undertaken a research project to quantitatively assess the value of a terrace garden in a residential scale. A garden patch of about 15 m2 in area, a typical size available in most urban terraces is developed. Surface temperatures are measured over a period of 15 months between July 2018 to January 2020 using four thermocouple sensors, placed within and outside the garden bed, on and below the roof. We compare the thermal performance of the terrace garden across years, seasons, time of the day, presence or absence of garden bed and type and height of vegetation. The surface temperature data was found to correlate well with the ambient air temperature values. The results show that the terrace garden moderates and stabilises the ceiling temperatures and reduces it by about 2–3 °C in winter months and 5–7 °C in hot summers. The garden also provided nearly 400 g of fresh monthly vegetable harvest per m2 of garden. Further, the cooling impact of the terrace garden with natural, tall, wild vegetation is higher as compared to planted vegetation. The study demonstrates a sustainable approach to terrace garden design at residential scale through quantified dual benefits of temperature control within buildings and urban farming.