Extreme heat is one of India’s most urgent climate risks, and its effects are especially severe in cities. Dense built-up areas absorb and retain heat, driving the urban heat island effect, where urban neighbourhoods stay 3°C–5°C hotter than rural surroundings, often with no relief at night. Cool roofs offer a simple, cost-effective, and scalable solution to safeguard vulnerable communities, reduce urban heat islands, and strengthen climate resilience.

Chennai, one of India’s largest and fastest-growing cities, faces increasing urban heat stress due to rapid urbanisation and high ambient temperatures, with temperatures frequently exceeding 40°C and indoor heat stress disproportionately affecting low-income communities. The report builds on the findings of the cool roofs pilot conducted at the Light House Project in Perumbakkam, Chennai, where cool roofs were installed and monitored for improvement in indoor thermal comfort. The study provides empirical evidence on temperature reduction, thermal comfort improvement, and the potential for citywide adoption, as well as a city-level framework to accelerate the adoption of cool roofs by generating evidence of their impacts at the local level.

Key Insights:
• Reduced heat gains: Cool-coated roofs reduced outdoor surface temperatures by 9°C–12°C and indoor temperatures by 0.5°C–1.5°C, improving thermal comfort by 20% for residents.
• Affordable and scalable: Energy savings of up to 12% make cool roofs a cost-effective passive cooling strategy, with citywide adoption requiring a modest share of municipal budgets.
• Financial estimation framework: Estimated investment of around ₹390 crore (US$44 million) for residential rooftops and introduces a GIS-based methodology, inspired by solar rooftop assessments, to guide citywide planning and investment decisions.
• Identified barriers: Financing gaps, weak policy mandates, limited workforce capacity, and low awareness continue to hinder large-scale adoption of cool roofs. Addressing these systematically is critical to unlocking their full potential.
• Learnings from global narratives: Experiences from India and abroad show diverse adoption pathways — from community-led rollouts in Ahmedabad, to state-wide mandates in Telangana, and building code requirements in California — offering valuable models for scaling in other contexts.

Pathways for Change
The report presents a clear Think–Do–Scale framework that helps cities move from pilots to large-scale adoption of cool roofs. This approach outlines practical steps to:
• Think: Identify heat-vulnerable hotspots, assess locally relevant solutions, and define technical specifications.
• Do: Implement pilot projects at scale, integrate cool roofs into policies and housing programmes, and build workforce capacity through training.
• Scale: Institutionalise adoption by embedding cool roofs into urban planning frameworks, supported by financial incentives, awareness campaigns, and community engagement.
This structured pathway provides city leaders with a clear roadmap to accelerate action, helping cool roofs move beyond isolated pilots to become a large-scale urban heat mitigation strategy.

Read more in the report.