# A Review of Indoor Air Quality in Social Housing Across Low- and Middle-Income Countries
## 3 Results of the Literature Survey
### Retrofit and Maintenance (R&M)  
The reviewed studies in this category used a variety of retrofit and maintenance strategies to improve IAQ and thermal comfort, including architectural modifications, simulation studies, and cooling measures. Bioclimatic strategies have been shown to effectively improve IAQ and thermal comfort. [PERSON] et al. [41] evaluated 351 affordable households in Colimo, Mexico, where 70% of kitchens and 62% bedrooms were reported as too small, with the residents relying heavily on fans (71%) to mitigate insufficient airflow. A bioclimatic prototype unit was designed and constructed, incorporating cross-ventilation through divider walls, stack effect ventilation with strategically placed openings, shading devices, and solid clay brick walls (0.15 m thick) to block solar radiation and increase thermal mass. All these strategies effectively addressed ventilation issues in existing affordable housing. Similarly, [PERSON] et al. [42] investigated the performance of various improvement options for social housing design in Ecuador across four climatic zones. They analyzed the impact of modifications to building envelope, ventilation openings, and insulation. Improvements such as adding roof gaps and window overhangs increased comfort by up to 25% in tropical climates, while temperate zones required additional insulation to achieve only slight improvements (7%). Also, [PERSON] et al. [43] found vegetated walls reduced heat loss by 38% during the day and absorbed dust and noise, offering a cost-effective retrofit option for urban housing. While bioclimatic designs provide replicable frameworks, they often focus on specific geographic and climatic conditions (e.g., sub-humid and tropical zones), thus limiting their generalizability to other climates. Moreover, most studies evaluate interventions under idealized conditions, which may not account for the variability in resident behavior, such as window usage. [PERSON] and [PERSON] [44] conducted a survey in social housing in Indonesia that revealed that residents frequently invested in renovations to address significant deficiencies such as missing kitchens, cracks, and inadequate drainage systems, as well as dissatisfaction with building materials. These resident-led improvements showed the need for better construction standards in social housing. Similarly, [PERSON] and [PERSON] [45] used computer simulations to show low-cost adjustments in improving IAQ in Mumbai's rehabilitation housing. Their interventions increased air velocity to 0.3 m/s and significantly reducing PM2.5 concentrations in the breathing zone by optimizing furniture and ventilator placements. Several studies used advanced simulation systems to control IAQ in high-density housing. [PERSON] et al. [46] used a parametric approach to improve the energy efficiency of Mexican social housing using the EnergyPlus simulation software version 23.1 to model thermal performance and energy efficiency under specific climate conditions. EnergyPlus simulated heat transfer through building elements, occupant behavior, and HVAC performance, while jEPlus, which is a parametric simulation manager for EnergyPlus, analyzed various passive design strategies like insulation thickness, window-to-wall ratios, and material properties. These multi-objective optimizations significantly improved thermal performance and promoted natural ventilation. The study identified three building elements that achieved optimal energy efficiency in the Mexican tropical climate. Double-glazed windows reduced convective heat transfer and gains and achieved up to 72.6% energy savings with reflective coatings. Roof insulation with expanded polystyrene (EPS) foam, with an optimal thickness of 8 cm, improved the thermal performance and reduced cooling loads by around 20%. Window warnings effectively minimized solar heat gain, reducing interior temperatures and improving thermal comfort, especially in warmer months.