Measuring the fabric performance of UK dwellings

An airtight and well insulated thermal envelope is crucial for the development of low energy and low carbon housing. Although this is widely recognized, there is mounting evidence, in housing at least, that the U-values achieved in practice can be much higher than those calculated, and that the gap between the predicted and the actual measured thermal performance of the building envelope can be substantial. This paper describes an approach that can be used in the field to measure the fabric performance of dwellings, a co-heating test. The paper also presents the results from 15 co-heating tests that were undertaken on dwellings that were built to conform to or exceed the insulation requirements contained within Approved Document Part L1A 2006.Whilst the total number of dwellings reported here is small, the results suggest that a significant gap can exist between the predicted steady state heat loss and the measured heat loss, and that this gap can be as much as 125%. This is likely to have significant implications in terms of the energy use and CO2 emissions attributable to these dwellings in-use.