Science and Innovation

PhD in architecture and urban planning, she is a postdoctoral researcher at the Barcelona Institute for Global Health (ISGlobal). She is also principal investigator of the HABITAS project, which in 2020, in the midst of the COVID-19 pandemic, received one of the Scientific Research Awards on Urban Challenges in the City of Barcelona 2020 granted by Barcelona City Council. As a result of this project, Carlota Sáenz de Tejada and her team have studied the effect of the quality of the air in our homes on health and have developed a practical guide to ventilate the home effectively and reduce exposure to pollutants. We talked to her about this little-known type of pollution, its relationship with the environment and health, and what we can do to mitigate its impact.

Is there pollution inside our homes?

Yes, of course there is. Studies indicate that the air inside our homes can be up to five times more polluted than the air outside. However, we are generally unaware of this and, while we increasingly measure and know more about outdoor air quality, indoor environments (and particularly those in the home) remain largely unknown. But we are talking about a major health issue: the World Health Organisation (WHO) estimates that polluted indoor air caused 3.2 million deaths worldwide in 2020, compared to 3.5 million attributed to outdoor pollution.

What factors influence the air quality at home?

Every home is different. We can find huge variations between flats even within the same block, as indoor air quality is influenced not only by the type of construction and where the home is located, but also by other factors such as the number of people living together (and if there are pets), the furniture we choose, the type of kitchen, or our habits in terms of ventilation, cleaning, smoking, burning candles or incense…

What are the most common pollutants in a house?

The most common pollutants in the home have evolved over time, as our building systems and habits as a society have changed. We know more, for example, about the dangers of the use of asbestos (now banned and being removed from buildings that still have it in some of their construction elements), as breathing in its fibres can cause various types of cancer. There is also greater awareness of the danger of indoor radon gas accumulation (especially in poorly ventilated basements and bathrooms) and its carcinogenic effects.

In addition, the widespread use of fuels such as coal, wood or biomass for cooking and heating in Europe is fortunately moving away from the widespread use of these fuels, which give off particulate matter (PM) with significant effects on respiratory, cardiovascular and reproductive health. However, it still occurs in some cases, especially in conditions of energy poverty. And we still have indoor sources of PM that can harm our health, such as some gas cookers or heaters (especially when frying or grilling food), wood-burning fireplaces, smoke from tobacco, candles or incense; or the accumulation of house dust, pet hair and dander. In fact, it is estimated that about 80% of the burden of disease from exposure to polluted indoor air in the EU is caused by exposure to PM_2.5.

How does insulation affect the home?

Over the years, dampness and the proliferation of mould (associated with respiratory and asthma problems) are generally reduced thanks to thermal insulation, which greatly reduces the risk of condensation forming. The construction trend in recent decades has been in the direction of better insulation of dwellings, thus preventing energy losses and increasing their airtightness. This can have multiple health benefits – physical, mental and social – but at the same time it is being found that the reduced ventilation patterns that often accompany these increased insulation measures can have a negative impact on indoor air quality: the air is no longer renewed as much as it used to be. This is aggravated by the emergence of a multitude of synthetic materials and coatings in our homes, which release particles and volatile organic compounds (VOCs) that have even been shown to be carcinogenic in some cases. For these reasons, it is more necessary than ever to stress the importance of properly ventilating the home to renew the indoor air and prevent the concentration of pollutants that are harmful to our health.

What about the outside environment?

Outside sources of pollution can enter the home through cracks or gaps, or through open windows. This is the case, for example, of nitrogen dioxide (NO₂), sulphur dioxide (SO₂), ozone (O₃) or particulate matter (PM). In addition, warmer temperatures due to climate change may encourage occupants to open their windows more often, possibly coinciding with periods of high ambient ozone levels, resulting in increased indoor exposure.

Even so, in an urban environment like Barcelona, is it still recommended ventilating our homes?

Without a doubt. As I said, indoor air in our homes can be much more polluted than outdoor air. We have indoor sources of pollution that, if not dispersed through ventilation, can reach very high levels of accumulation that are harmful to health. But, of course, we also need to consider what kind of air we are bringing into our homes when we open the windows. And it is understandable that people who live in areas of the city with high levels of outdoor pollution may wonder whether it would be better to leave the windows closed. Therefore, as far as possible, it is advisable to avoid ventilating during peak traffic hours, for example. And in very severe cases in areas with very high levels of outdoor pollution, the use of air filters and air purifiers could also be considered.

What other environmental factors inside flats can affect people’s health?

There are many. For example, temperature and humidity, to achieve what is known as “hygrothermal comfort” conditions. It is also essential to have natural light (sunlight) in the dwelling and not to be exposed to noise levels that are harmful to our health (especially during sleeping hours). Exposure to electromagnetic fields is also a subject under study, the long-term effects of which are still largely unknown. In addition, there are spatial and functional aspects that have also been shown to be essential for health, such as accessibility, or sufficient space and number of rooms in relation to the number of people living together.

What is meant by “healthy housing”?

There is no official definition of what we mean by “healthy housing”. But as a result of our work on housing and health, we understand it as housing whose characteristics and conditions protect our physical, mental and social health, and promote a comfortable and active lifestyle. This means ensuring favourable indoor environmental conditions in terms of temperature, humidity, natural light, air quality, water quality, noise or electromagnetic fields. But it also means guaranteeing their use by people with functional and/or cognitive limitations, being accessible, spacious…

It should be noted here that the concept of housing goes beyond its interior conditions; in fact, the WHO adds to the dimension of physical housing other dimensions such as the immediate environment and the community. Healthy housing therefore implies living in a safe, connected environment, close to basic resources and services, opportunities for mobility, training and work, where one can establish social connections and actively participate in the community. It also implies being able to access housing in an equal and non-discriminatory way, and without the associated costs entailing the renunciation of other basic needs such as education, healthcare, or healthy food.

Are Barcelona’s homes healthy?

It is difficult to generalise, as there is a wide variety of typologies and urban fabrics. The Observatori Metropolità de l’Habitatge de Barcelona (Barcelona Metropolitan Housing Observatory) has carried out some studies on the subject. For example, dwellings built between 1940-1960 suffer from a lack of natural light and ventilation. Also, logically, older buildings have major accessibility problems, with the significant impact on physical, mental and social health that this has on the elderly and/or people with reduced mobility.

We also have, in general in Spain, little access to open spaces in our homes. This is something that many of us have suffered during our confinement. We should think about how to make more use of common spaces in housing blocks, including communal roofs where possible.

How should we ventilate homes?

The Ventila por tu salud guide provides some criteria and recommendations on how best to ventilate our homes, with recommendations on the frequency and duration of ventilation adapted to the Barcelona context, and according to a variety of housing typologies. As we explain in this guide, not all homes require the same ventilation guidelines, nor do they all have the same facilities to ventilate effectively. Ventilation guidelines will also depend on the time of year, as we must take into account the heat loss that ventilation can cause in the colder months, as well as the importance of creating air currents for greater comfort in the warmer months. Generally speaking, however, cross ventilation should be carried out (where possible), for several minutes (depending on the case) and several times a day (especially when there are more people in the house).

We have also created a short web-based questionnaire of ten questions about people’s homes, which can help those interested to get recommendations more specific to the characteristics and conditions of their particular home.

And how can we know the pollution levels in our home?

There are a multitude of sensors on the market that can help us to identify when it is more convenient to ventilate because the indoor environment is more polluted. These sensors are usually based on the levels of CO₂ that accumulate inside the home, and can also represent the accumulation of other pollutants such as PM. Although they provide limited information on indoor air quality, they can be a resource to help us in our daily ventilation habits.

As a society, what do we need to do to ensure the health of people in their homes?

According to the WHO, nine out of ten people in the world breathe unhealthy air. As we spend most of our time (and more and more of it) indoors, indoor air quality becomes increasingly significant and potentially dangerous to our health. We must continue to work towards improving indoor air quality as a public health and equity objective, through research, public policy, and by increasing public information and awareness.

The HABITAS project emerged in the context of the COVID-19 pandemic. What was its objective?

The HABITAS project focused on the study of the links between housing and health from the perspective of indoor air quality. The COVID-19 pandemic highlighted the importance of renewing indoor air to reduce the risk of infection (in this case, very much focused on the spread of the virus). But, as mentioned above, this importance of renewing the air also has to do with reducing the levels of other health-damaging pollutants. In addition, the housing confinements we experienced in 2020 also brought to light the significant deficiencies in our housing stock.

It was time to explore these housing-health-indoor air quality relationships, and we set out to do so through mixed-method research, combining indoor air quality (IAQ) monitoring in a sample of 30 homes in the city of Barcelona over one year, with interviews with residents about their perceptions and ventilation habits. We also set out to create the basic ventilation guide, Ventila por tu salud, to which we then added a web tool, all of which is open access and available.

What have you discovered?

Through monitoring, we collected 15 million pieces of data on different CAI indicators that we are still analysing. But in terms of the most remarkable results found so far, we have seen several things. To begin with, IAC gets noticeably worse in winter (vs. summer and in-between seasons). This is because people tend to ventilate less in winter, to preserve heat. Then, IAC is generally worse during the afternoon/evening, in line with reported ventilation habits. That is, most participants reported ventilating only in the mornings, after getting up. And this has proven to be insufficient to ensure good IAC. On the other hand, with similar ventilation habits, IAC is more effective on high floors (above the 3rd floor), where good or very good levels are maintained throughout the year. This is something we already sensed: for lower and first floors, it is more difficult to ventilate effectively.

What else?

Those dwellings that cannot create draughts, or have difficulty doing so, experience higher average daily temperatures in summer (> 27°C). This makes them particularly vulnerable during episodes of extreme heat, which are becoming more frequent and intense as a result of climate change. Despite the fact that Barcelona has mild winters, 40% of the dwellings studied experience a lack of comfort due to cold. This tells us that, in addition to considering the risk of heat, efforts should continue to be made to protect dwellings from the cold. And finally, in those dwellings with smokers, PM2.5 levels exceed the WHO threshold (even when they report not smoking in the monitored room).

What has the support obtained thanks to the Scientific Research Awards for Urban Challenges in the City of Barcelona 2020 meant for the project?

The project would not have been possible without this support. It has been an opportunity to explore the issue of health in housing, which is rarely possible, as it involves a great effort of data collection and collaboration with volunteer participants. It has also, for me personally, been a huge learning experience about what is involved in leading and managing such a project, an opportunity that young researchers rarely get before the age of 40.