The rising heat in Tamil Nadu and across India is beginning to worsen the environment. In 2025, The Hindu reported that mercury levels peaked at 39.2°C and 39.7°C in Nungambakkam and Meenambakkam, respectively. The series of summer forecasts issued by the India Meteorological Department indicates a surge in heatwaves across the country in April.

Similar conditions are expected to follow in subsequent months, calling for a broader programme of tree planting, lake rejuvenation, park and open space design, and green roofs.

Of the many initiatives to mitigate the harsh impact of heatwaves, the green roof concept lends itself to citizen participation. For several decades now, apartment terraces in Chennai have been a largely derelict space.

In the absence of precise data, vast areas of terrace spaces lie neglected across the State. A citizen’s participation, incentivising the judicious greening of terraces and roofs may have several benefits.

In October 2024, the Tamil Nadu government declared extreme heat as a State specific disaster, and was the first State in India to declare it. This led to policy initiatives such as the integration of UN Environment Programme’s passive cooling guidelines into the Green School Programme. The next stage would be the formulation of guidelines and broader public awareness. 

The need for cooling the urban environment and for design that keeps buildings cool, especially affordable housing, is the need of the hour. On another front, the Environment, Climate Change and Forests Department, along with the Department of Education and Tamil Nadu Green Climate Company, has initiated the cool roof and passive cooling campaign for over 700 schools, with an objective to improve thermal comfort in all 38 districts. A cool roof uses reflective materials to reduce heat absorption and help keep indoor temperatures lower. In contrast, a green roof comprises layers of vegetation that provide insulation, keeping buildings cooler in summer and warmer in winter.

As for green roofs, they have been initiated elsewhere in India and several parts of the world. Terraces covered with greenery, vegetation, herbs and plants have several benefits, including substantially reducing the heat in the top floors of apartment blocks and other building typologies.

Most green gardens on terraces begin with a selection of plants that are robust and can grow with the least maintenance. Herbs such as tulsi (holy basil) have been traditionally grown in Chennai for generations. Several kinds of spinach (keerai), too, have been grown, besides curry leaves (karuvepilai), chilli, and tomatoes. With consistent care, these plants can survive the hot-humid weather of Chennai.

The Urban Thottam project, a Chennai Resilience Centre Initiative, supported by the Adrienne Arsht Rockefeller Foundation Resilience Centre, has provided a forum for such initiatives.

The main challenges have been to create public awareness, alongside guidelines on maintenance, costs, selection of plants, terrace waterproofing standards, and water availability to landscape gardeners.

“We are measuring the extent to which edible terrace gardens can help with heat adaptation and to improve thermal comfort. Preliminary findings reveal that on average, 6 am to 6 pm, the room directly below the garden is 2-3°C cooler than a room below an exposed terrace, with the maximum temperature difference going up to 7 °C,” says Ayesha Ajmal, research associate and communications manager at Chennai Resilience Centre.

According to Krishna Mohan Ramachandran, chief resilience officer, Rooftop edible gardens (REGs) offer a nature-based, community-driven solution to urban heat stress while delivering multiple co-benefits related to nutrition, learning, and wellbeing. He says, “Evidence from schools in Chennai shows that REGs can significantly reduce heat exposure, lowering indoor temperatures by 1–2°C, roof surface temperatures by 8–12°C, and ceiling temperatures by 2–4°C during peak heat periods. Despite these benefits, current urban heat policies in India remain largely focused on cool-roof technologies, with limited recognition of rooftop greening and no formal integration of REGs.”

In addition to substantially cooling the environment, green roofs also contribute to biodiversity. These will also lower the risk of urban flooding if designed to collect and store rainwater. Combined with alternative rainwater harvesting systems, these systems can absorb almost 60% of rain and recharge groundwater as well. In certain projects with larger open spaces, almost all the rainwater can be contained to reduce the risk of urban flooding.

According to the official website of the Tamil Nadu Water Supply and Drainage Board, stored rainwater can help to recharge local aquifers, reduce urban flooding and, most importantly, ensure water availability in water-scarce zones.

In the absence of awareness campaigns and training programmes, resident associations are wary of adopting green roofs. For instance, citizens fear that green roofs can result in water leakage. Waterproofing of terraces is essential before initiating such projects. Timely maintenance is crucial, too. Ecological practitioner Divya Manimaran, who worked at Auroville, notes that heat stress can affect plant health, while termites from the soil may damage wooden elements in the house. Maintenance can be difficult, especially during travel periods. Properly designed water drainage is also essential to avoid related issues. “A green net can help shield plants from direct heat, while choosing appropriately sized pots with proper overflow outlets will ensure good drainage. Regular watering at fixed times or through a simple drip irrigation system will keep plants hydrated, and adding cocopeat will help retain soil moisture,” she says. “Nutrient support through NPK inputs or jeevamrut can aid healthy growth, while neem oil will work as a natural pest deterrent, alongside other organic solutions suited to specific plant types and local conditions.”

At the fourth Tamil Nadu Climate Summit held in February, organised by the Department of Environment, Climate Change and Forests (DoECCF) along with partner institutions, Dr. Sowmya Swaminathan, chairperson of the M.S. Swaminathan Research Foundation, spoke about the importance of biodiversity in efforts to conserve nature and restore ecological balance. In this context, green roofs emerge as a practical intervention — one that can help revive the biodiversity steadily being eroded by expanding urban concrete.

In rapidly growing cities such as Chennai, the loss of open space is evident. Safe areas for the elderly and children are fast depleting, too. In this context, a transformed terrace can act as a community space for the apartment, including a creche and other facilities. 

The Chennai Metropolitan Development Authority (CMDA) has initiated a series of nature-based projects, rejuvenating lakes, and conserving and creating parks. The United Nations Global Watch report recognises Tamil Nadu and its pioneering progress in conserving nature. Environmentalists and citizen groups, awaiting the Third Master Plan (to guide growth over the next two decades, 2026 to 2046) and the Tamil Nadu Combined Development and Building Rules, hope the CMDA will mandate green rooftops, enabling housing projects, both public and private, to integrate these measures alongside renewable energy.

For the green roof initiative to thrive and transform the city, the most essential would be active civic participation. A sustained awareness campaign by environmental institutions in collaboration with media houses could set the foundation for a climate-responsive urban environment, with green terraces as the protagonist for quality of life.

The writer is an architect, academician and the founder of Artes Roots Collaborative.