By Rajneesh Sareen, Programme Director, Sustainable Habitat Programme, Centre for Science and Environment, New Delhi, India

The rising episodes of heatwaves are placing an enormous public health threat on the population of India by pushing them out of thermal comfort. The sixth assessment report of the International Panel for Climate Change 2022 points to the fact that heat stress will rise so much that a third of the global population will live outside thermal comfort, beyond adaptive capacity by 2070.^[1]

The recent heatwave stifling north India conveys that this public health threat is looming closer while maximum temperatures remained above 45°C in the states of Haryana, Delhi, Rajasthan and Uttar Pradesh.^[2]

Unfortunately, there is no mechanism or measure in place that protects or prepares the people from extreme heat, let alone the vulnerable groups. Cities at the moment are only taking ad hoc measures. For instance, Kolkata has planned cool cabins which are glass cabins fitted with air conditioning and placed in public areas. With only a handful of these cabins operational, this strategy has already failed in one of the largest urban centres of India.^[3] This shows that cities need something more grounded and effective in the long term.

Heat stress does not affect everyone in the same way. While the elderly and children are more vulnerable to heat, the poor, especially those who work outdoors are more vulnerable to the rising heat. Heat-trapping material used in informal settlements like roofs made of tin, tarpauline and galvanised iron sheets combined with prolonged exposure to the sun leads to high vulnerability of the poor.

An analysis by the Centre for Science and Environment (CSE) revealed that 75 per cent of slum dwellers are living in the most heat stressed areas in Kolkata. This calls for appropriate mitigation measures with a priority to the shelter of the vulnerable population.

India Cooling Action Plan was launched in 2019 to enable thermal comfort for all. It aims at providing thermally comfortable housing to the poor by adopting Eco Niwas Samhita 2018 – the Energy conservation buildings code for residential buildings. Other than this, the National Building Code 2016 also suggests temperatures for cities at which adaptive comfort can be achieved. Overall, research has brought a few considerations for designing housing:

Climate Responsive Design

Building envelopes should be designed such that they respond to the movement of the sun and harness the effect of natural wind. The east and west façade of the house should be fortified so as to not allow the harsh sun in. Staircases and storage areas are a few such options. While the southern façade faces the sun, appropriate shading devices or chajjas can allow the warm winter sun and block the harsh summer sun. Similarly, there are many passive design techniques that can enable buildings indoors to remain cool or cut down a few degrees on the Celsius scale.

Compliance with Emerging Codes

Eco Niwas Samhita 2018 lays focus on the insulating property of materials known as thermal transmittance value (or U-value). This parameter combined with a few others gives the residential envelope transmittance value (RETV) of the building as part of the code. RETV of residential buildings must be below 15 Watts per sqm (W/sqm). However, a CSE study found that most of the affordable housing is currently achieving RETV between 15 and 18 W/sqm.^[4] New affordable housing must focus on complying to the Eco Niwas Samhita 2018.

Traditional Wisdom, Modern Use

The role of materials in providing thermal comfort has become more important than ever before. The use of mud, cob, thatch and bamboo is quite popular in India to make houses that can withstand harsh temperatures. Architects have hybridised these materials by using them in walls and adding strength to the structure through a reinforced concrete cement frame. Such techniques can substantially lower the indoor temperatures.

Other than this, cool roofs made of terracotta tiles or brick bat coba have been used traditionally to prevent heat ingress from the roof. Broken tile chips reflect the sun and reduce the surface temperature by a few degrees. Reflective paints are becoming a popular quick solution to do the same. Green roofs that are partially or completely covered with vegetation can also bring respite from heat.

[1] https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter08.pdf

[2] https://www.thehindu.com/news/national/swathes-of-north-india-reel-from-severe-heatwave-conditions-delhis-najafgarh-hottest-in-country/article68198588.ece

[3] https://www.deccanherald.com/india/fatal-heat-waves-are-testing-indias-ability-to-protect-140-crore-people-3026690

[4] https://www.cseindia.org/guidelines-for-affordable-housing-in-telangana-11116

Disclaimer: The views expressed in this piece are those of the author/s and do not necessarily reflect the views or policies of AIDMI.