Performance gap in ‘deep’ retrofit of housing : issues at the design and construction interface

Deep energy efficient retrofit of hard to treat (HTT) properties is emerging as a major concern in the UK. A number of studies have highlighted the difficulties of effective delivery of this type of retrofit, citing issues of lower than expected performance, known as the ‘performance gap’. The aim of this chapter is to investigate the different factors that drive this performance gap when conducting deep retrofit in the UK’s ageing housing stock. Here, a series of semi‐structured interviews was undertaken with recognised retrofit experts in the UK, including architects, energy consultants, contractors and sub‐contractors who were actively involved in energy‐efficient retrofitting of HTT properties, to identify key performance gap factors. The study reveals that the major issues in such projects associated with the performance gap predominantly present themselves in the design and construction interface. The respondents identified a num- ber issues including: understanding and skills, working practices, and the physical uncertainty around HTT properties. These issues raise questions as to the position of deep retrofit as a solution to HTT retrofit, as not only a technical problem, but one of construction management, communication and, ultimately, industry culture