In the UK, boom periods of construction combined with typical building styles of the day, have resulted in a large stock of ageing office buildings at risk of structural vacancy and obsolescence. Despite their lack of insulation, high air infiltration, and solar gain, many such buildings from the 1960s-1970s are still in use today. Moreover, with UK buildings replaced at a rate of less than 2% a year, the majority of today's buildings will still be in use in 2050. Due to the impact of the facade on such aspects as thermal performance and aesthetics, façade retrofit is seen as a key solution to the problem of today’s ageing office building stock. Unfortunately, façade retrofit comes with a complex decision-making process. The cost and long-term nature of the investment means that façade decisions are strategic, while the architecture, engineering and construction (AEC) industry is prototypical and multidisciplinary. Decision theory suggests the use of normative decision-making methods to arrive at a well-reasoned course of action; therefore, this thesis aims to discover how decision-making can be improved to support façade selection in non-domestic building retrofit. A state-of-the-art literature review of office building façade retrofit decision-making only returned nine case studies, of which six reported real-life façade retrofit selection. One real-life and one theoretical case demonstrated the use of normative decision-making in the form of the payback period method, while one theoretical case used multi-criteria analysis. Many sources of information were revealed as guiding the façade selection process in general. To examine the actuality of façade selection in practice, an exploratory study was conducted. This study involved (1) semi-structured interviews on the topic of façade selection with thirty UK AEC industry members from twelve professions, and (2) a case study of an over-clad 1970s office building, involving in-depth interviews with two UK AEC industry experts, a documentary evidence review, and post-retrofit thermography. Three semi-structured interviewees revealed the use of normative decision-making, in the form of the payback period method, while information sources were greatly used in general. The exploratory case, however, revealed only a minimal use of information and no normative decision-making. To determine the representativeness of the exploratory case study, an in-depth study of façade retrofit decision-making was conducted. This study involved (1) a specific literature review to set the context of UK university building façade retrofit decision-making and (2) four exemplifying case studies of real-life university building façade retrofit. The university estate features many ageing buildings from the 1960s-1970s that exhibit the same typical building style as the UK’s ageing office stock. The specific literature review found five cases of university façade retrofit decision-making, of which three reported real-life façade retrofit selection. Normative decision-making was revealed in theory, with the two theoretical cases of university façade retrofit using the payback period method. The exemplifying case studies involved eight UK AEC industry experts, a documentary evidence review, and post-retrofit thermography. The case buildings ranged from the late 1950s/early-1960s to the 1970s, with three being over-clad, and one over-clad and re-clad. The exemplifying case study findings support the exploratory case study findings. The key actors in façade retrofit decision-making are the architect, client, and planner. Numerous information sources are used to support the façade selection process, relating chiefly to performance, cost, aesthetics, and collaboration, and the use of normative decision-making is not evident. From the research findings, it appears the process of façade retrofit selection functions naturally within the realm of the architectural profession. Architects appear to be making initial façade design decisions based on ideas resulting from cognition and drawing on past experience, which become more detailed as the project progresses. The façade selection process is supported by the voluntary use of numerous information sources, many of which are quantitative in nature. This thesis did not find evidence of normative decision methods being used in the current practice of façade retrofit selection. Thus, the recommendations proffered are not characteristic of normative theory, but instead opt to support the façade retrofit selection process by reinforcing current process via the following points: (1) use expertise in the form of advisor-led information sources to guide the façade retrofit selection process; (2) maximise communication by encouraging an ongoing dialogue between AEC industry members involved in façade selection, involving specialist external bodies at an early stage, and documenting the façade selection process; and (3) aid the energy efficiency resulting from building retrofit by engaging stakeholders during design, construction, and in-use, especially in regards to proposed new energy efficiency practices. This thesis contributes to the knowledge of non-domestic façade retrofit decision-making in actual building design practice. Having found only limited evidence of normative decision-making being used in the non-domestic façade retrofit selection process, it appears that efforts to develop multi-criteria decision-making tools for use in this area may be misguided.

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