A detr-sponsored seminar on healthier homes held at the bre recently* presented a picture that is not entirely reassuring. The effects on health of poor indoor air quality in homes give rise to concern. Minimum standards to achieve health are not easy to establish. Effective design solutions require decisions about the materials of construction, finishes, equipment, fenestration and ventilation.
Asthma - The incidence of asthma is increasing world-wide. In the uk there are some 2000 deaths a year and a very great deal of discomfort and disability. Asthma is caused by breathing in 'allergens', minute air- borne particles emanating from house mites, domestic pets and cockroaches. When a sufficient concentration is present in the air, sufferers experience irritation and swelling of the airways and have difficulty in breathing.
Housekeeping measures can exercise limited control. Special allergen- proof casings can be used to contain bedding. Vacuum-cleaning of carpets, bedding and furnishings using machines with high-efficiency filters will reduce concentrations for a time but will not solve the problem permanently. Chemical treatments perform similarly.
The design, construction and management of dwellings can produce environments which are unsuitable for house mites and thus control their number. Surfaces on which dust can accumulate should be avoided. Floors which do not require carpet are likely to have a valuable effect, as are measures which enable controlled natural ventilation to be provided. Good ventilation is necessary for the control of house mites. It is particularly important to ensure that moist air from kitchens and bathrooms does not escape into the remainder of the dwelling. In colder climates, winter internal relative humidities will be low, and this has been used to control house mites. In this country winters are relatively warm and this technique does not appear to be successful. However, concentration of allergens in the air may still be reduced by ventilation.
Mould - Growth of moulds is likely to be associated with inadequate ventilation or damp penetration, both of which can in turn be associated with conditions likely to affect health. But it was made clear that there is no evidence that mould growth itself is injurious to health.
Chemical air pollutants
Several speakers addressed the problem of chemical pollutants, which include carbon monoxide (co), nitrogen dioxide (no2), volatile organic compounds (vocs, such as formaldehyde) and fine particles. The scope and scale of pollutants is being investigated in four newly commissioned test houses at bre, and a wide range of materials is being tested for pollutant emissions in environmental chambers. Draft standards are being prepared.
Man-made fibres are widely used in buildings. Airborne fibres, if breathed in high concentrations, may give rise to skin and lung irritation but do not cause cancer. They are not regarded as a special health hazard to building occupants.
Some types of asbestos fibres are associated with lung cancer. The degree of exposure required to give a significant risk of lung cancer would arise only when working with the material. Normal occupancy of dwellings with asbestos in good condition is not regarded as a significant health risk. Precautions to take when working with the material are now universally applied, and it is more than 10 years since the material was used in new dwellings.
Where it is possible to chose equipment and finishes which do not generate pollutants, this is much to be preferred. However, ventilation must inevitably play a major part. Increased levels of ventilation have a beneficial effect on all aspects of air pollution, though they have to be balanced against heat loss. They control the levels of moisture within the dwelling and, as a result, affect house mite levels.
The Building Regulations normal requirement is for an opening light and a trickle ventilator in every room and, for bathrooms and kitchens, an extract fan or stack vent. The special vents for bathrooms and kitchens are intended to limit the penetration of moisture and odour into the remainder of the dwelling. Automatic closing of bathroom and kitchen doors, even if only by rising butts, would improve the control of moisture. Careful attention to the sealing of pipe ducts, which often distribute moist air, would also assist.
The Regulations do envisage two alternative mechanical ventilation systems which, in principle, should reduce levels of pollutants. One requires both mechanical supply and extract of air. It is effective but expensive. The other gives positive pressure using only input fans, taking air from the roof space. This was conceived as a measure to control condensation by displacing moist air. Unfortunately, it appears that most dwellings are not airtight enough to allow this system to achieve its intended results.
There is much work still to be done. Defining safe standards for buildings presents a particular problem. When people spend a large proportion of their time in dwellings, reaction to pollutants may only become apparent after long exposure to a low level of the particular agent. However, once the linkage has been made, further reactions can be instant and severe.
The detr is currently investing£1 million pa into research in this field at the bre. The aim is to ensure that advice on the harmful effects of pollutants is available to all by 1999.
Peter Burberry is emeritus professor of building engineering at umist
* Healthier Homes: Indoor Air, Health and Housing. Seminar at bre, 6 May 1998