Redesigning chawls to allow fresh air

The cities are growing at a rapid pace and houses are becoming smaller and expensive. Especially for low income households, the houses they can afford has deprived environment with higher than recommended temperature and humidity. While living in such environments are known to cause breathing problems, heart diseases, frequent body ache and headache, the lack of objective data that can help in the reconstruction of such houses is lacking. In a first-of-its-kind study, researchers from the Indian Institute of Technology Bombay have investigated how living in ill-ventilated dwellings, like the chawls, could affect the health of the inhabitants and have provided some objective recommendations on restructuring these houses.

In this study, published in the journal Habitat International, the researchers examined the living conditions of 120 households of the chawls, built by the erstwhile Bombay Development Department (BDD), in four regions of Mumbai. The chawls, originally designed as a living space for just one person, has only about 200 sq.ft area. It has a kitchen accommodated within the living area and shared toilet blocks on the sides of the building. The suffocated living space, lack of maintenance and hygiene, pollution from the adjoining roads and use of kerosene-like fuels for cooking with poor ventilation affects the quality of life of the people staying here.

Although the local authorities had observed a steady increase in the number of visitors to health centres from these areas and had suspected the poor air quality to be the culprit, they could not back the claim with data. The occupants of the chawls did not wish to reveal health-related information. The frequency of their visits to the local health clinic was all the occupants were willing to share—a data point the researchers of the study made use of to indicate the health of the occupants.

The researchers chose a metric called ‘local mean age’ (LMA) of the air to indicate the air quality. “The mean age of air is defined as the average time that a mass of air has spent in a zone of the building accumulating contaminants,” explains Prof. Ronita Bardhan who led the study. It is an important factor in assessing the quality of ventilation. Simply put, it indicates period for which stale air stays inside a room, before being replaced by fresh air. Thus, a properly ventilated room has a low value of LMA, since fresh air is continuously circulating. Experimental studies show that if a building zone has both doors and windows closed, then the LMA values are near 46 min whereas, when the same doors and windows are open the LMA values can be as low as 3 mins. LMA is also a metric that is easy to understand and explain in the local language---Marathi--- say the researchers.

The researchers considered factors like the orientation and direction of the building, the presence of parks, roads and obstructions around the building, the area of the building, the thickness of its walls and the ratio of the areas of the windows and the walls. They surveyed the occupants on how long they kept the doors and windows open. They also used the local weather data along with data from temperature and humidity sensors placed in a few households. They used this information and mathematical models simulations to estimate the LMA values. 

The results of the study indicate that occupants of well-ventilated houses, where the air was fresh, made fewer visits to healthcare centres than those living in ill-ventilated dwellings. However, there was no significant association between the freshness of the air and the number of health care visits. 

The researchers observed that external obstructions played a significant role in the determining LMA and removing them could reduce the LMA values by half. Cross-ventilation in the buildings could also improve the freshness of the air. However, these changes need policy-level actions to make suitable modifications and raise awareness among residents about the need for living areas with fresh air, say the researchers.

“The involvement of local authorities would enable us to have better access to the indoor living environment of the chawls. We can study the human-space interactions of the residents in real-time and enable design sensitisation of living spaces among the occupants,” say the authors.

The findings and recommendations of the study could act as a significant input for planning authorities who could change the design of these buildings and help the residents of the BDD chawls live a relatively healthier life.