This study explores the thermal performance of informal dwellings in Dhaka, Bangladesh. Its focus lies on a typical informal building in the Hazi Road slum area at Mirpur 1. The paper demonstrates how the thermal comfort of interior living spaces of such inadequate housing can be improved with minimal changes in the building structure and minimal cost. Urban slums constitute a significant portion of many cities in developing and emerging countries. These informal settlements are particularly prevalent in cities where rapid population growth, migration, and poverty converge with weak or missing infrastructure and urban planning. As a result, urban regulations often fail to apply, leading to inhumane and unacceptable living conditions. It is indisputable that life quality and living conditions must be substantially improved for this significant portion of the world's population. In Bangladesh, as in many tropical regions, informal housing suffers severely from poor indoor environmental conditions. Common issues include excessive heat, high humidity, insufficient natural ventilation, and indoor air pollution. The use of inefficient, unventilated cookstoves primarily causes the latter. This study highlights the inadequacy of current living conditions by simulating poor indoor comfort levels, specifically focusing on excess heat. It presents proposals for improving interior comfort, especially temperature and air quality, showing that significant improvements can be made with relatively low effort and cost. How can existing informal dwellings be transformed with minimal architectural intervention to reduce indoor air temperatures and air pollution levels optimally? The study employs a mixed-methods approach, combining a detailed case study analysis of informal dwellings in Dhaka with computational building performance simulations (using Climate Studio) to assess indoor thermal conditions. The simulations compare baseline scenarios with proposed low-cost interventions, focusing on passive cooling strategies. Results are analyzed to demonstrate gains in thermal comfort and reductions in air pollution due to better ventilation, ultimately informing evidence-based retrofit recommendations. Simulations of the case study building showed that indoor conditions exceeded the thermal comfort threshold (28°C, 70% humidity, < 0.3 m/s air flow) on about 235 days annually. However, simulations of the same case study building, but with an optimized design, showed significant improvements, reducing temperature exceedances to 1–5°C on about 137 days and 5–10°C on only about 7 days per year. This study demonstrates that a much better interior comfort in informal housing in tropical climates can be achieved almost immediately with minimal modifications. Significant improvements are showcased with these low-effort interventions. Further studies, e.g. deep analyses, energy performance simulations, site visits, measurements and testing, would be essential to refine the intervention proposals presented in this paper. The efforts provided could strongly enhance living conditions not only for the estimated 3.5 to 4 million slum dwellers in Dhaka, but also for the tens of millions of people living in similarly challenging environments across tropical and hot humid regions worldwide.