The relationship between indoor air quality (IAQ) of homes and its impact on the health of its occupants is a subject of recurring concern for experts in the field, but the arrival of Covid-19 made it a priority for the housing sector.

The principal parameter to calculate IAQ are the concentration ratios of CO₂, which should not be more than 900 ppm (parts per million), as established by the regulations. Experts believe that the concentrations of carbon dioxide above 1000 ppm are detrimental for health, harmful over 2500 ppm and serious at 5000 ppm.

Recently, The General Council of Technical Architecture of Spain (CGATE) carried out a pioneer investigation to assess the accumulation of CO₂ inside Spanish homes. According to the "Study on indoor air quality in homes", the concentration of carbon dioxide in most homes exceeds the established limits.

The study was done in 31 homes, located in different regions of the country, during 9 days uninterrupted. The measurements confirmed that in 58% of the living rooms, the concentration of CO₂ was higher than 900 ppm, meaning, unhealthy for their inhabitants. Although this is not the worst place in the house. 71% of bedrooms exceeded the limit and if the door was closed the percentage increased to 100%.

The type of windows in the house influences indoor air quality. Paradoxically, houses with better quality windows are those with higher concentrations of carbon dioxide. Homes with hermetically sealed windows in 81% of the bedrooms and in 75% of the living rooms surpassed 900 ppm. Housing without this type of insulation in the windows exceeded the healthy threshold in 57% of bedrooms and 43% of living rooms.

The age of the buildings is also a relevant parameter when calculating the IAQ. In 2006, the Technical Building Code was published which emphasized the importance of good thermal insulation. However, insulation provokes an increase in the concentration of CO₂ in the interior of houses.

From these cases, we understand that the new buildings have windows and closings in accordance with regulations and that the buildings constructed prior require rehabilitation to comply with the same.

Given that airtight insulation leads to a higher percentage of ppm, a second phase of the study is expected to be focused on improving home ventilation systems.