Rooms beneath rooftop gardens were found to be 1°C or 2°C cooler than those beneath exposed roofs, while the gardens reduced roof surface temperatures by eight to 12°C, according to a study by IIT-Madras and Okapi Research and Advisory carried out in various sites of Chennai.

The findings highlight the potential of rooftop gardens to reduce heat exposure in buildings and provide a nature-based cooling solution for Chennai’s increasingly warm urban environment. The study also revealed that such gardens helped moderate the amount of solar energy absorbed and reduced ceiling temperatures by two to 4°C.

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The institutions conducted a series of studies to check the impact of urban rooftop gardens on thermal comfort and indoor temperatures across four sites — Adyar, Chromepet, Otteri, and Adambakkam — in Chennai. These gardens were set up at sites, including government schools and residential buildings, by Chennai Resilience Centre, a voluntary organisation. The study found that the cooling effect was pronounced during specific periods indicating peak cooling potential of such gardens, noted researchers.

For instance, in Adambakkam, the garden-covered room recorded 33.7°C at 5 p.m. on September 25 last year, compared with 37°C in the room without a roof garden, indicating an indoor temperature reduction of 3.2°C.

Similarly, the garden-covered room in Adyar recorded 32.1°C at 6 p.m. on September 26 last year, compared with 34.3°C in the room without a garden — a dip by nearly 2.2°C.

Parama Roy, executive director, Okapi Research and Advisory, said, “We also noticed a difference in ambient temperature by nearly 8.1°C between garden-covered and exposed roofs in Otteri during June 2022. The ambient temperature over the garden-covered roof was 35.7°C, compared with 43.8°C over the exposed roof. The temperature reductions are consistent.”

Various sensors, including radiation and temperature sensors, were used to measure incoming and outgoing radiation, temperature at the roof surface, ceiling, and different heights above the roof.

“The study has demonstrated that rooftop gardens have a potential as a passive cooling strategy for vulnerable communities and importance of integrating into broader urban cooling and heat stress resilience strategies. The government must consider rooftop gardens as an affordable complement to other heat mitigation strategies,” she said.

The institutions are looking to explore how the building-scale benefits could be scaled up to the city-level. For instance, how converting 20% to 30% of the urban terraces into rooftop gardens could influence the intensity of urban heat island effect and help mitigate heat stress, researchers said.

Published - August 11, 2026 05:00 am IST