Are homes making people sick? We explore with practical solutions offered.

New research unveiled by UK’s Cartwright Pickard Architects and the Mackintosh Environmental Architecture Research Unit (MEARU) suggests that improved energy efficiency in homes may be having unintended consequences for occupants’ health.

In 2008 the UK government made a commitment that by 2050 it would have reduced carbon emissions by 80%. Since then regulatory attention has focused on improving energy and carbon performance, for example through increased insulation and airtightness, and more efficient heating.

However, carbon-blinkered technical ‘innovation’ is encouraged based on what looks interesting or might sell rather than what actually works. This has set the industry on a path to unintended health consequences, with problems caused by, for example, inadequate ventilation, evaporation of volatile chemicals into the air, and reduced standards of space and light. The resulting health risks are both physiological (respiratory disease, diminished immune system, diabetes, obesity) and psychological (seasonal affective disorder, depression).

Europeans, for example, spend 85-90% of their time indoors, whether at home, work, school or leisure. Over the years there have been major changes to building design and materials; to the furniture, finishes and equipment purchased; and to the ways in which they are used. At the outset of the 20th century, approximately 50 materials were used to construct buildings. By the end of the century, this list had grown to around 50 000, half of them being synthetic. Compounds implicated in indoor air quality toxicity are emitted from the building materials, furnishings and fittings, cleaning products and, somewhat ironically, even air fresheners. One result has been to amplify the effects of indoor environments on occupants’ health.

Cartwright Pickard Architects and the Mackintosh Environmental Architectural Research Unit (MEARU) carried out a study of 20 newly built properties across London, investigating how they performed compared with predicted performance during design stage The research aims to focus on health and wellbeing rather than energy efficiency, its long-term aim being to identify gaps between predicted and actual performance and to devise practical solutions to close them.

The properties studied by Cartwright Pickard and MEARU had all been designed to meet performance levels above the regulatory minimum. Modern residential properties are designed to a high level of airtightness in order to reduce energy consumption. As a result they are heavily reliant on their ventilation systems to maintain a constant supply of fresh air and keep indoor airborne pollutants at a safe level.

Internal CO2 levels are used as an indicator of air quality – while CO2 concentrations would need to reach extreme levels to be directly harmful to humans (4 000ppm-plus), levels above 1 000pm (parts per million) are seen as an indicator of poor ventilation. This can have consequences through the accumulation of pollutants such as VOCs given off by modern building materials and furniture, etc, as well as increased moisture levels leading to dust-mite proliferation and mould growth, which can lead to asthma.

The project team monitored a total of 20 dwellings over a two-week period during three different seasons, typically summer, winter and spring, in order to evaluate the dwellings’ performance in different climatic conditions.

During each season, the following aspects were monitored:

1.    Energy performance Data was gathered by taking meter readings (gas, electricity and photovoltaic, where applicable) of the occupants’ energy use over the two-week periods to understand the comparative energy use over each season. Energy use was also recorded over a 12-month period.
2.    Internal environmental conditions were assessed using Eltek GD-47 transmitters and RX250L data loggers to measure temperatures, relative humidity and internal CO2 concentration levels. Sensors were located in the living room, kitchen and two bedrooms (typically). A sensor was also used to monitor the external conditions of the micro environment (temperature and relative humidity levels). This provided information on the typical temperatures maintained at the property and gave an indication of the indoor air quality.
3.    Occupant behaviour Information was gathered on the household type and size, occupancy patterns, use of the building systems, ventilation regimes and occupants’ opinions on their property relating to space and layout. This information provided context to the indoor environmental data.
4.    Build quality: Thermographic investigations were carried out during the winter monitoring season to identify any missing insulation (cold spots) and heat loss through the building fabric caused by thermal bridging. The ventilation system was tested to check whether the recommended ventilation flow rates were being achieved.

The findings from the study indicate there are significant gaps between the predicted and actual performance of the dwellings – both in terms of energy use and environmental performance. The indoor air quality within these 20 dwellings is a particular cause for concern. The ventilation provision adopted at the dwellings’ design stage is not performing adequately, with research identifying problems of design, construction quality, installation and commissioning, occupant interaction and maintenance. A series of design and build quality issues causing low internal temperatures in the dwellings and affecting occupant comfort was also identified.

•    CO2 concentrations rose above the threshold level in 95% of the properties monitored.
•    Indoor CO2 levels were worst in winter, with concentrations rising above the recommended level of 1 000ppm for 54% of the occupied hours. In some properties CO2 levels were found to be over 2 000ppm for sustained periods of time, with peaks of 3 250ppm not uncommon.

Several factors were found to contribute to inadequate ventilation and high CO2 levels:

•    Ventilation systems were often badly installed and incorrectly commissioned.
•    Ventilation units were also poorly maintained. Most commonly the air filters had not been changed or cleaned, reducing the airflow through the system and restricting the ability to extract stale air and supply fresh air.
•    The majority of the MVHR systems tested failed to meet the Building Regulations’ advisory airflow rates.
•    Trickle vents above windows were either non-existent, closed or covered by curtains or blinds, reducing the flow of fresh air into the properties.
•    Most of the properties overheated during the summer months, in part because of excessive solar gain from unprotected full-height windows, but exacerbated by underperforming ventilation systems failing to extract sufficient stale, warmed air to keep spaces ventilated.

11 Strategies to address these findings
Following the research, the report recommends the following points to be considered by the project shareholders:

1.    Design approaches to building performance. 
These should be more intensely considered, going beyond building control box-ticking and seriously considering strategies for heating and ventilation. This should begin at early design stages with a consideration about usability and purpose of selected strategies and development of performance standards.
2.    Building systems handover.
Identify an effective handover strategy for dwellings’ occupants. All 20 occupants from the study recognised the importance of a face-to-face handover of the building systems. Their top two suggestions for improving this were: (a) to consider the time of the handover, making it closer to the start of the heating season and (b) that the person delivering the handover was knowledgeable about the building systems. Most of the occupants also preferred a hard copy of the handbook to a DVD – a few elderly occupants felt a DVD was not user-friendly.
3.    Lifecycle costs.
Recognise the whole-lifecycle costs associated with the maintenance of MVHR systems, including filter changes.
4.    Heating controls.
Consider simple and intuitive heating controls that will enable occupants to use the heating system efficiently.
5.    Alternatives to radiators. 
It is increasingly common to position radiators against internal walls opposite the windows and behind internal doors rather than on outside walls below windows, often because of space constraints. This leads to thermal gradients and draughts. Where radiators cannot be positioned on the external wall, consider other options such as skirting-board radiators on the external walls, or underfloor heating.
6.    Heating and ventilation strategies
Strategies need to balance demand for energy efficiency, while delivering sufficient fresh air for good internal air quality. This is particularly critical for occupants who smoke indoors. The study identified that in 30% of the dwellings monitored, occupants smoked indoors during the winter, keeping their windows or external doors ajar while using space heating.
7.    Controlling unwanted heat gains.
These can be significant in well-insulated buildings and in the summer this can lead to overheating. This should be avoided through intelligent design and seasonal shading.
8.    Trickle vents. 
In the case of floor-to-ceiling-height windows ensure the trickle vents and window controls are easily accessible by the occupants, especially in dwellings with elderly occupants.
9.    Dedicated indoor drying area. 
Consider a ventilated indoor drying area to deter occupants from drying clothes on radiators and in bedrooms.
10.    Mechanical ventilation units. 
Consider the nature and purpose of MVHR and MEV systems. In an airtight house they are the sole means of ventilation so it is important to get them right and ensure they work. Ductwork is especially vulnerable – it should be large, short and straight.
Units should be easily accessible to enable regular maintenance. It is important that at the project’s design stage the registered social landlord considers the maintenance regime and decides who will be responsible for changing filters, and that access is provided for this.
In dwellings with MVHR systems, all habitable rooms should have supply vents. During the commissioning of the ventilation system, the flow rates should be set to achieve advisory requirements of 8 litres of fresh air supply per occupant.
11.    Floor-to-ceiling-height windows. 
Consider making the lower panel of any floor-to-ceiling-height windows obscure, so occupants have privacy without compromising the level of natural light to their rooms.


Cartwright Pickard believes that architecture is both an art and a science. They advise that architects should challenge the established norms of best practice when project outcomes are not acceptable. They also believe that good architecture must improve the occupants’ quality of life, not just look fashionably attractive with kerb appeal.

According to them, the UK has one of the highest levels of asthma in the developed world. They believe there is a correlation between this and the increasing airtightness of new homes, which has resulted in poorer indoor air quality. This case study makes for an insightful read when considering similar factors and attributes in South Africa.

Their survey has shown that most of the MVHR systems in the dwellings studied were not correctly installed or commissioned and were seldom maintained properly because of the hassle and cost involved. MVHR systems should be carefully scrutinised with regard to lifecycle costs and practicality in use. If not operated and maintained correctly, the air quality in a home quickly deteriorates without occupants realising it.

There are simpler and more practical alternative mechanical ventilation systems on the market, which do not require filters and which can respond to occupational density and varying conditions within each room or dwelling.

The study also found that most residents were ill-informed about the controls and technology in their homes. The heating and ventilation controls in most of the homes were over-complex so residents had trouble understanding how to use them correctly.  Most residents complained they had been given little or no face-to-face introduction to the controls and systems in their new homes, and that even the property managers had a poor understanding of them.

The problems with air quality outlined in this feature are just some of the many serious problems this research project has identified. The next stage is to engage with the industry to disseminate and share the findings from their research and to help develop solutions. To that end they will be hosting a half-day seminar at the British Library on November 19 with the theme ‘Health and Wellbeing in New Homes’. There they will present their findings in detail and will be joined by leading figures from education and industry. They believe architects, engineers, developers and house builders will all benefit from this event.

Acknowledgement and thanks go to For more information on the seminar, email