Bridging the domestic building fabric performance gap

Abstract

In the UK, it is recognised that there is often a discrepancy between the measured fabric thermal performance of dwellings as-built and the predicted performance of the same dwellings and that the magnitude of this difference in performance can be quite large. This paper presents the results of a number of in-depth building fabric thermal performance tests that were undertaken on three case study dwellings located on two separate Passivhaus developments in the UK; one masonry cavity and the other two timber-frame. The results from the tests revealed that all of the case study dwellings tested performed very close to that predicted. This is in contrast with other work that has been undertaken regarding the performance of the building fabric, which indicates that a very wide range of performance exists in new build dwellings in the UK, and that the difference between the measured and predicted fabric performance can be greater than 100%. Despite the small nonrandom size of the sample, the results suggest that careful design coupled with the implementation of appropriate quality control systems, such as those required to attain Passivhaus Certification, may be conducive to delivering dwellings that begin to 'bridge the gap' between measured and predicted fabric performance. KeywordsAir tightness, building performance, housing, thermal barrier, coheating, heat flux. ContextOver a number of years, it has become evident that there is often a discrepancy between the predicted energy and thermal performance of a building and the measured performance of that building in-use. This discrepancy is often referred to as the 'performance gap'. The 'performance gap' affects domestic and non-domestic revealed discrepancies between the measured and predicted energy and thermal performance of whole buildings, or individual building elements. The reasons identified for the discrepancies in performance tend to be widespread and highly context specific. Despite this, they can be broadly categorised into three main areasthose relating to the thermal performance of the building fabric, those relating to the energy performance of the building services and those relating to occupancy. It is also important to recognise that all three of these areas are also influenced by the external environmental conditions. This paper is concerned with the thermal performance of the building fabric in new UK dwellings only. Despite this, the findings from this paper are likely to be equally applicable to other building types both within the UK and abroad. 2

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