Major new research into home ventilation and health identifies need for definitive safe minimum level of ventilation; no comprehensive study on how home ventilation ensures health; insufficient knowledge of ventilation rates in UK homes, impacts of ventilation systems and occupant behaviour; need to learn lessons from other countries Code for Sustainable Homes (CSH) fails to stipulate low emission construction products.
The report is summarized as follows:
There is a clear imperative to make homes more energy efficient, but in order to deliver that objective we are making the built fabric of the home significantly more airtight. That in turn is driving a shift away from a reliance on windows and building permeability towards the adoption of ventilation systems, whether natural/passive or mechanical. In fact mechanical ventilation with heat recovery (MVHR) becomes necessary in order to meet Code for Sustainable Homes (CSH) energy requirements at code levels 5 and 6.
An adequate ventilation level for a home is generally 0.5 to 1 air changes per hour. This is considered sufficient to keep relative humidity levels below 70 per cent most of the time, thus inhibiting condensation and mould growth.
While standards and regulations govern the building of new homes, refurbishment of existing ones generally involves work that is not covered by Building Regulations, and is therefore carried out without scrutiny. Needs for ventilation are seldom considered, even though houses can be made significantly more airtight by actions such as adding insulation or sealing old air bricks, etc. Studies have also indicated that many new and existing homes are not well ventilated, with occupants often failing to use ventilation systems where they are provided.
Some of the potential impacts on the health of occupants are outlined here, together with the effects of energy efficiency measures.
Indoor air pollutants
What are they: The air inside the home can contain varying levels of a range of pollutants. Common indoor pollutants include volatile organic compounds, chemicals used in the manufacture of common household items such as insulation, paints and furnishings, and carbon monoxide and nitrogen dioxide from gas appliances and smoking.
Impacts on health: Symptoms have been found to include respiratory complaints (e.g. hoarseness, cough) and dryness of the skin.
Impacts of energy efficiency measures: Appropriately maintained mechanical ventilation systems with filtration of fine particles in the incoming air can reduce exposure to ambient particles. Research backed by the Canadian government has shown occupants experience improvements in throat irritation, coughs, fatigue and irritability after moving into new airtight homes with MVHR systems. However, the same study found that occupants were not necessarily using the MVHR systems correctly.
Mould and mites
What are they: High levels of relative humidity will encourage condensation, growth of mould and proliferation of house dust mites.
Impacts on health: Both mould and dust mites are associated with respiratory conditions, most notably asthma.
Impacts of energy efficiency measures: An absence of condensation and mould are generally taken to indicate that a home has sufficient ventilation. As with indoor air pollutants, the use of MVHR can help.
Overheating
What is it: There is no statutory maximum internal temperature in UK building regulations or health and safety guidance. The Technology Strategy Board report, Design for future climate, draws attention to a Chartered Institution of Building Services Engineers/Arup study which defines ‘warm’ as 25oC and ‘hot’ as 28oC. That study defines 35oC as the temperature above which there is a significant danger of heat stress.
Impacts on health: The summer heatwave of 2003 resulted in more than 2,000 extra deaths in the UK. There is increased risk of illness and death from a number of conditions, most commonly respiratory and cardiovascular disease. Warmer temperatures may also result in higher levels of ozone gas, which can be an irritant.
Impacts of energy efficiency measures: Some measures, such as insulation, may increase internal summer temperatures. Night-time ventilation assumes greater importance in hot weather and there are concerns about the capabilities of mechanical ventilation to deliver the eight air changes an hour recommended for adequate cooling. It is therefore important that passive measures to limit overheating, such as shading, are incorporated into new builds and refurbishments to reduce dependence on air conditioning.
Radon
What is it: Radon is a radioactive gas that comes from the decay of radium, which is found in small quantities in soils and rocks and is particularly prevalent in granite and limestone areas. It is drawn from the ground into a building by differences in atmospheric pressure, levels of which are lower inside the building.
Regulations: The Health Protection Agency recommends homes are fitted with radon protective measures, such as a gas-tight membrane at ground floor level.
Impacts on health: Radon is estimated to be responsible for more than a thousand cases of lung cancer each year in the UK.
Impacts of energy efficiency measures: Indoor radon levels may be increased by some measures and decreased by others. Double glazing of windows is reckoned to increase indoor radon levels by more than 50 per cent. Sealing unused chimneys and the fitting of underfloor insulation may reduce ingress.
Conclusion
There is already strong evidence that energy efficient homes have a positive impact on occupants’ physical and mental wellbeing. Basic improvements in indoor temperature levels in winter and reduction in fuel poverty can have a significant impact. But there is a shortage of evidence to inform decision-making in this area and it is vital that risks to public health are not increased.
There are a number of areas where more knowledge is needed. Although 0.5 air changes per hour is the accepted norm, we lack a definitive assessment of a safe minimum level of ventilation. There is no comprehensive study on the part that home ventilation plays in ensuring health. We have insufficient knowledge of the actual ventilation rates being achieved in UK homes, impacts of ventilation system design, installation and operation, and impacts of occupant behaviour.
We should also be learning the lessons from other countries, several of which now have standards or packages specifically for air quality in sustainable housing. The CSH does not stipulate the use of construction products that have low emissions levels and so have the minimum negative impact on air quality. The European Commission is working to harmonise existing voluntary schemes for labelling of low-emitting products and there is clearly scope for such a scheme to be adopted in the UK.
Sources and links
Indoor air quality in highly energy efficient homes – a review is a useful publication on this topic. NHBC Foundation Report NF 18, July 2009 is available at www.nhbcfoundation.org
Building 4 Change: LINK
