IIT Madras Study Finds Rooftop Gardens Cut Indoor Temperatures Across City

A study by IIT-Madras and Okapi Research and Advisory conducted across Adyar, Chromepet, Otteri, and Adambakkam has found that rooftop gardens significantly reduce indoor temperatures and roof surface heat in Chennai. The research evaluated the thermal impact of urban rooftop gardens set up at government schools and residential buildings to assess their potential as a nature-based cooling strategy.

According to the findings, rooms situated beneath rooftop gardens were 1°C to 2°C cooler than those under exposed roofs, while the gardens reduced roof surface temperatures by 8°C to 12°C. The study also revealed that these gardens moderated the amount of solar energy absorbed by structures, lowering ceiling temperatures by 2°C to 4°C.

The rooftop gardens evaluated during the study were established by the Chennai Resilience Centre, a voluntary organisation. To conduct the thermal assessments, researchers deployed various instruments, including radiation and temperature sensors, to measure incoming and outgoing radiation, surface temperatures, ceiling temperatures, and heat levels at different heights above the roofs.

The research documented clear cooling effects during specific observation periods across test sites. In Adambakkam, a garden-covered room registered 33.7°C at 5 p.m. on September 25 last year, compared to 37°C in a room without a roof garden, representing an indoor temperature reduction of 3.2°C. In Adyar, a garden-covered room recorded 32.1°C at 6 p.m. on September 26 last year, compared to 34.3°C in a room without a garden, marking a dip of nearly 2.2°C.

In Otteri, researchers observed an ambient temperature difference of nearly 8.1°C above the roof during June 2022. The ambient temperature over the garden-covered roof reached 35.7°C, compared to 43.8°C over the exposed roof.

Parama Roy, executive director of Okapi Research and Advisory, stated that the study demonstrates the potential of rooftop gardens as a passive cooling strategy for vulnerable communities, adding that the government must consider rooftop gardens as an affordable complement to heat mitigation strategies. The participating institutions are now planning to explore how converting 20% to 30% of urban terraces into rooftop gardens could influence the urban heat island effect across the city.