By Akash Yadav, AIDMI, India

Maharashtra’s urban heat strategy has primarily focused on tree cover, public awareness campaigns, and the use of indoor fans. However, in slum homes with tin roofs and limited airflow, these measures address only the real risk in part. During pre-monsoon weeks, indoor temperatures routinely exceed safe physiological limits, even at night. This isn’t just discomfort; it’s a public health emergency playing out in slow motion across millions of homes. Yet some of the most effective solutions require no power, no machinery, and minimal cost.

Drawing on 10 peer-reviewed studies and large-scale pilots, the table below highlights passive cooling approaches — such as reflective coatings, simple insulation, and improved ventilation — that deliver measurable relief. Crucially, they are light enough for fragile structures, cheap enough for informal budgets, and scalable enough for policy.

Below is the same evidence table shared earlier; it lists the source, the intervention tested, headline results, and why each matter in the Maharashtra context.

Table: Literature Review of Cool-Roofing Solutions in India

Take-home Lessons for Practitioners

1. Paint first, then insulate.
   Field trials across four Indian cities show that a single lime-based or acrylic reflective coat typically cools rooms by 1 – 4 °C (with rare peaks up to 5 °C). Adding a thin Thermocol or bamboo-jute layer roughly doubles the relief, delivering 6–13 °C lower highs compared with bare tin, depending on whether you benchmark against outdoor air or an unmodified roof.
2. Design for air.
   Energy Plus simulations and spot monitoring in Mumbai’s Dharavi show that introducing true cross-ventilation or leaving a modest 15 cm pergola gap above the roof can reduce overheating hours by approximately one-quarter to two-fifths (≈ 22 – 39 %), with zero electricity input.
3. Fans need context.
   After a basic cool-roof retrofit, peak indoor temperatures in Ahmedabad tin-roof homes stay below 35 °C. Electric fans remain helpful up to that threshold but can increase heat strain once the air exceeds ≈ approximately 39 °C in hot, dry conditions. In the cooled rooms, the fan is therefore both safe and effective.
4. Scale multiplies gains.
   City-scale modelling for Ahmedabad shows that coating just 20 % of roof slices 0.21 TWh yr⁻¹ off projected 2030 cooling demand and nudges daytime neighbourhood air temperatures down by ~0.6 °C, enough to push several “danger” heat-index days back below public-health thresholds.