Thresholds needed to tackle overheating homes
The industry urgently needs to come up with new guidance on temperature thresholds to prevent new build or refurbished homes suffering from overheating, a new report is urging.
The study, carried out by the Zero Carbon Hub public-private advisory group and the NHBC, also found evidence that prototype houses built to zero carbon standards can suffer from overheating issues. Overheating in New Homes was based on a review of existing studies, consultation with house building experts, housing practitioners and other industry professionals.
It found evidence that new and refurbished properties are increasingly at risk of overheating, especially small dwellings, flats and single-sided properties where cross ventilation is not possible. Homes where cross ventilation was not achievable in lightweight, airtight houses with little or no solar shading proved particularly problematic.
The study found that homes’ ability to reject the heat build-up from normal occupant activities was most noticeable in summer, but in some instances overheating occurred for most of the year and seemed to rise independently of the external temperature. The findings also raise concerns over the health implications of overheating, the report states: “The medical evidence shows that although the health effects of exposure to excessive heat can be mild, if left untreated symptoms have the potential to develop quickly into severe, often fatal heat illness.”
To avoid future problems with overheating, the report recommends development of a universally accepted definition of overheating in dwellings, and development of a set of robust national thresholds for use by planners, designers, builders and authorities.
Whether such thresholds are regulated, for instance through the Building Regulations, is also a “key issue for debate and action”, the report states.
The report also calls for greater guidance and modelling tools based on robust, practically proven research, as current methods seemed unable to correctly predict overheating.
These should include a practical assessment of the effectiveness of thermal mass and night-time ventilation in new dwellings. The report states: “Much of the modelling suggests that this may be very effective, but models often make assumptions of perfect control, and the sensitivity of the effectiveness of thermal mass to night-time ventilation needs to be determined in order to deliver robust designs.”
In response to the report’s findings, Keith Riddle, managing director at window manufacturer Velux, said: “New homes that resemble hermetically sealed boxes could become the norm as developers strive to meet increasingly strict energy efficiency standards. The NHBC’s research will, we hope, mean that many developers will now pause for breath and consider adequate ventilation as a viable means to building affordable zero carbon homes that are also healthy places to live.”