Interstitial Spaces as Heat-Resilience Buffers: Indoor–Outdoor Thermal Assessment in Kolkata’s High-Density Low-Income Settlements

Heat exposure disproportionately affects marginalised low-income urban communities. Though included in the expanded city limit currently, informal settlements remain excluded from mainstream urban climate resilience opportunities. Global South is grappling with urban heat challenges, especially in informal settlements, owing to unregulated growth and densification, heat-entrapping interstitial spaces and diminished open green spaces. Well-being is contested in such settlements; however, their indigenous coping mechanisms increase their heat tolerance level. The user-centred approach to heat stress adaptation in low-income settlements is a highly relevant, but often under-prioritised aspect of planning and governance in India. Therefore, this study enquires about forging adaptive solutions that integrate indoor to outdoor interstitial spaces in high-density, low-income settlements in the warm-humid eastern Indian city of Kolkata. The UN-Habitat report and the city’s metropolitan authority mention a 4.7% annual urban growth and 25.5% green cover reduction, leading to a 4.72 °C peak temperature rise in Kolkata, intensifying heat risks in low-income settlements. Using a practice–theory approach, this study analyses socially embodied heat adaptation practices with data-driven geo-spatial simulations among low-income dwellers to develop an inclusive climate-resilient model. The framework is examined in a high-density, low-income settlement in Kolkata, located near a mixed-use commercial-industrial hub. A study of urban growth maps interprets the high thermal risk zones validated through field visits. ENVI-met simulation with open-source indoor thermal flow is used to assess indoor–outdoor heat dynamics, offering context-specific adaptive solutions. Simulation-based strategic retrofitting of wall openings that correlate with outdoor interstitial spaces can create contiguous indoor–outdoor cooling dynamics, reducing heat stress. Cost-efficient interventions, such as pocket greens, portable wall-mounted and rooftop greens along elastomeric coatings or mod-roof panels, indigenous measures like wet gunny-bag screens on windows, help 2-5 °C reduction in indoor temperature. Hence, this study advances scalable community-level interventions aligned with UNSDGs 11, 13, and 17 towards inclusive urban heat resilience.