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Are our homes making people sick?


New research by Cartwright Pickard Architects and the Mackintosh Environmental Architecture Research Unit suggests improved energy efficiency in our 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 per cent. Since then regulatory attention has focused on improving energy and carbon performance, for example through increased insulation and airtightness, and more efficient heating. There is a trend to mandated complication in building design and specification, even though building performance feedback suggests that it is difficult to get even the simple things right. 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 spend 85-90 per cent 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 we put into them; and to the ways in which we use them. 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 55,000, half of them 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 our health.

Cartwright Pickard Architects and the Mackintosh Environmental Architectural Research Unit (MEARU) have carried out a study of 20 newly built properties across London, investigating how they performed compared with predicted performance during design stage (see above). 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.

Cartwright Pickard is a research-led practice with a history of technical innovation, while MEARU, part of the Glasgow School of Art, has been active in building performance evaluation for many years. The research was part of a Knowledge Transfer Partnership (KTP) initiative, with funding provided by Innovate UK (IUK), formerly the  Technology Strategy Board. MEARU had previously carried out a range of studies as part of the IUK building performance evaluation programme, as well as a number of related studies, including investigations into energy and environmental impacts of domestic laundry practices, occupant use of trickle vents and investigations into MVHR (mechanical ventilation with heat recovery) systems. This work has identified a range of problems leading to performance gaps.

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 20 properties monitored are representative of the housing stock built by London’s biggest contractors for well-known housing associations, the major producers of housing in their boroughs. The houses were designed and built to Code for Sustainable Homes levels 3 and 4, Eco homes ‘very good’ rating and in accordance with the Building Regulations. The dwellings incorporated energy-efficient strategies such as high levels of thermal insulation, airtight buildings with whole-house ventilation systems and high energy performing windows.


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 Internal 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 our research identifying problems of design, construction quality, installation and commissioning, occupant interaction and maintenance. We also identified a series of design and build quality issues causing low internal temperatures in the dwellings and affecting occupant comfort.

Adopting a light touch approach, the building performance evaluation provided the occupants and the housing managers with a continuous update on the performance of these dwellings and, in certain situations, suggested cost-effective interventions (for instance in situations where occupants switched off the MVHR system because it was too noisy, or where filters were blocked).

Key Findings

CO2 concentrations rose above the threshold level in 95 per cent of the properties we monitored.

Indoor CO2 levels were worst in winter, with concentrations rising above the recommended level of 1,000ppm for 54 per cent of the occupied hours. In some properties we found CO2 levels over 2,000ppm for sustained periods of time, with peaks of 3,250ppm not uncommon.

We found several factors contributing to inadequate ventilation and high CO2 levels:

• Ventilation systems were often badly installed and incorrectly commissioned. This was particularly prevalent with MVHR systems, which need to be carefully installed and balanced to gain maximum operating efficiency.

• Ventilation units were also poorly maintained. Most commonly we found 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 (see photographs, page 31).

• The majority of the MVHR systems tested failed to meet the Building Regulations’ advisory airflow rates.

• Trickle vents above windows were either nonexistent, 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. The summer bypass function required by MVHR systems to reduce overheating was often not working or incorrectly set up.


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 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. Occupants also felt it would be useful to include heating and ventilation strategies in the handbook – for instance, summer ventilation strategies with night-time cooling, and strategies for controlling the thermostatic radiator valves (TRVs) to control air temperatures in individual rooms. Forthcoming Scottish Building regulations include a requirement for occupant guidance based on previous work by MEARU).

3. Life cycle costs Recognise the whole-life-cycle cost 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 under-floor heating.

6. Heating and ventilation strategies   Strategies need to balance demand for energy efficiency, with delivering sufficient fresh air for good internal air quality. This is particularly critical for occupants who smoke indoors. The study identified that in 30 per cent 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. Consider solar shading for dwellings facing south and west, which are likely to suffer solar gain and glare.

8. Trickle vents In 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.


Flexible ductwork installed in Dwellilng 01

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.


Condition of air filter cleaned two weeks previously in Dwelling 01

In dwellings with MVHR systems, all habitable rooms should have supply vents. These should be positioned in a central location on the ceiling to enable proper mixing of the air.The flow rates in dwellings with MVHR should be balanced; the rate of air being extracted from the dwelling should be equal to the rate of fresh air being supplied. During the commissioning of the ventilation system, the flow rates should be set to achieve advisory requirements of 8 litre/s 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.


At Cartwright Pickard we believe that architecture is both an art and a science. We like to ask questions. Why? Because questions lead to answers, answers lead to ideas, and ideas lead to progress. We also believe that architects should be prophets who reinvent the wheel when required. Architects should challenge the established norms of best practice when project outcomes are not acceptable. But how many architects actually measure the performance of their buildings?

Despite being one of the largest industries in the UK, construction invests very little in research and development and rarely measures the performance outcomes of the buildings it produces. We believe that good architecture must improve the occupants’ quality of life, not just look fashionably attractive with kerb appeal.

Since the mid-1970s oil crisis, the UK’s Building Regulations have steadily increased the levels of insulation and air tightness in our homes without considering the unintended consequences of living in such highly sealed buildings.

The UK has one of the highest levels of asthma in the developed world. We believe there is a correlation between this and the increasing airtightness of new homes, which has resulted in poorer indoor air quality.

Our two-year government-funded research project has reinforced recent concerns expressed by organisations such as BSRIA (Building Services Research and Information Association) that the air quality in many new homes in Britain is not good enough. Research carried out by MEARU has demonstrated that trickle vents in windows often don’t work as intended, for many reasons.

MVHR systems have become the ubiquitous default solution to achieving carbon targets and SAP ratings in urban housing. But our survey has shown that, in the dwellings we studied, most of the MVHR systems were not installed or commissioned correctly and were seldom maintained properly because of the hassle and cost involved. Regulatory dogma has shot the industry in the foot. MVHR systems should be carefully scrutinised with regard to life-cycle costs and practicality in use. If not operated and maintained correctly, the air quality in a home quickly deteriorates without occupants realising. There are simpler and more practical alternative mechanical ventilation systems on the market, which do not require filters and that can respond to occupational density and varying conditions within each room or dwelling.

We 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 our research and to help develop solutions. To that end we will be hosting a half-day seminar at the British Library on November 19 with the theme ‘Health and Wellbeing in New Homes’. There we will present our findings in detail and will be joined by leading figures from education and industry. We believe architects engineers, developers and housebuilders will all benefit from this event. You are all welcome to ask questions.

At Cartwright Pickard we try create architecture from the means of construction, but if the means of construction are flawed the architecture will inevitably be flawed.  Change is needed and soon.

James Pickard, director, Cartwright Pickard. For details of the seminar, email: weaskquestions@cartwrightpickard.com


Readers' comments (10)

  • A thought provoking and helpful article. I live in a 5-6 year old code 4 town centre flat. During the winter it is the warmest home I have ever lived in with the large south facing windows giving a general temperature of 20degreesC with even the smallest showing of sunshine on even the coldest days. Its the most energy efficient (cheapest) home I have ever lived in. However, during the summer it gets warm, really uncomfortably warm and relying on the MVHR system leaves me waking up groggy and parched. I admit that while I wouldn't describe it as noisy the sound is noticeable. The all electric radiator heating is tied into a central control system which the building manager advised us to avoid when we moved in due to its complexity. We just turn them off and on as we see fit, but even the individual radiator controls are overly complex with lots of symbols but no clear/useful explanation for all the various options, even in the manual.

    With the flat having been purchased by a buy to let landlord who didn't even bother looking at the flat before buying never mind having it professionally surveyed I don't hold out much hope for the next tenant understanding the first thing about the systems installed, and I bet any money that they don't have the first idea/intention of maintaining the filters on the vent system.

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  • Really interesting article and describes many of the issues I face in my 3 year old code 3 for sustainable homes flat. MVHR that actually isn't and is too noisy to run at night, fully glazed south facing windows that cause overheating. time clock hidden on the inside elevation of a cupboard. But very low heating bills and we leave windows open most of the time.
    biggest problem is that no one who lives in the flats really understands that there is a problem

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  • Chris Roche

    An excellent, thought provoking article and research. Similar studies need to be undertaken to examine how un-healthy our schools and workplaces are. Hopefully at some point the profession will wake up to the realisation that the criteria for award winning buildings needs to reflect meaningful innovation, rather than stylistic novelty.
    Chris Roche Founder 11.04 Architects

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  • It would appear that you were monitoring window opening as well. Is that correct? Did the occupants not open windows when the internal environment became poor? Were there noise or security problems?
    Our results of monitoring in CSH4 homes have not found particularly poor environments despite non-functioning MVHR systems...

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  • Ben Derbyshire

    A really informative article and a great example of the benefits of research.

    There is a European movement we have become aware of through our involvement with Velux prototype housing design (http://www.hta.co.uk/projects/velux-carbonlight-houses) called the 'Active House Alliance'. This is intended as a vision of buildings that create healthier and more comfortable lives for their occupants without negative impact on the climate. The focus is on healthy indoor climate and the benefits of very large amounts of natural light allied to natural ventilation. HTA's Rory Bergin is involved in setting up a UK chapter and would welcome contact with anyone interested.

    Ben Derbyshire
    Managing Partner, HTA Design LLP
    Chair, The Housing Forum.

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  • It would appear that you were monitoring window opening as well. Is that correct? Did the occupants not open windows when the internal environment became poor? Were there noise or security problems?
    Our results of monitoring in CSH4 homes have not found particularly poor environments despite non-functioning MVHR systems...

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  • Bob, in my CFSH4 flat I am in a town centre. Because of poorly regulated bars and clubs and particularly due to the government lifting restrictions on live music acts there is a very real noise problem, particularly at night. The MVHR system was apparently installed to combat the noise issue.
    Perhaps one of the problems is that with a heat recovery system any fresh air brought in is pre-warmed which is great in winter but not so great in summer, particularly since this is when town centre venues are more likely to open doors/windows and entire facades, or have live outdoor music acts.

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  • One way of regulating home temperatures is to diffuse natural sunlight (free from heat, UV) inside your home. Artificial light consumes a lot of energy (especially during the day unnecessarily), can cause health problems and radiates heat. There are technologies available which capture sunlight on the outside of buildings and transport it directly inside; giving you the highest quality of natural sunlight without heat! http://www.echy.fr/natural-light-and-architecture/?lang=en

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  • Really important research and essential reading. A couple of minor quibbles(!):
    - Energy efficiency per se isn't causing these problems, it's the strategies to mitigate knock on impacts that are falling short. This is made clear in the really sensible list of recommendations, but isn't reflected in some of the more emotive language in the opening and closing sections which I don't think is hugely helpful ("carbon-blinkered") and will be used as ammunition by those who would prefer to build to lower standards all round.
    - You can't say definitively that increasing levels of air tightness in new homes are behind the UK's high asthma rates. There must be so many additional considerations. There may be a link, but statements like that damage credibility.

    This is something the green building movement is taking seriously. See betterplacesforpeople.org for more information on an important initiative.

    John Alker
    Director of Policy & Communications
    UK Green Building Council

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  • Could you please let me know the title of this research paper? I cannot find any reference to it, and am therefore unable to quote it.


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