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This is a repository copy of Exploring the practices and roles of UK construction manufacturers and merchants in relation to housing energy retrofit.

Energy consumption in buildings is a large contributor to global carbon dioxide emissions. Renovations of existing buildings can reduce their impact by integrating technologies which increase efficiency or generate renewable energy on-site. Doing this well and at scale is a collective action problem, which transcends the agency of individual entrepreneurs. This article reports a cross-case comparison of four previous studies focused on low-energy renovation of housing, using a co-evolutionary framework in which five systems are mutually interdependent: ecosystems, technologies, user practices, business strategies and institutions. Innovations across the five systems are described in terms of variations, selection pressures and transmission. The analysis draws out common themes from the four previous studies and to reflect on how well the co-evolutionary framework accounts for innovation in the particular field of housing renovation for low-energy outcomes. Business strategies emerge as an important (and often neglected) source of innovation. The framework generally accounts for innovation in this area quite well, although two important issues are a less easy fit: The use of energy (and other finite resources) is rather indirectly accounted for by the term ‘ecosystems’ and the complexity of interactions between multiple users, businesses and technologies is partly elided.

This paper examines whether current residential retrofit metrics are fit for purpose and if they can help deliver swift and significant cuts in carbon emissions. Information is presented on metrics used for a variety of UK and European Union building and building retrofit standards and evaluation and assessment tools. An analytical approach is developed that offers a simplified set of four key aspects of metrics: scope, headline measurement, normalisation factor and timescale. This helps to unpack the complexity of metric design. However, choice of metrics is not simply a technocratic issue, because their design is not value free. Two examples where metrics form the basis for policy-making for retrofit and energy use in buildings are described: UK Energy Performance Certificates and the Energiesprong approach to deep retrofit. Use of multiple metrics improves their fitness for purpose and is already established practice in some standards and policy. Metrics in common use omit many aspects of energy use in buildings. New metrics are required that can take account of the whole life of a building, the time profile of retrofit, or the ability of the building to be flexible as to when energy is used. Policy relevance• Existing and new metrics can contribute to the transformation of the building stock. They have real-world impacts on buildings, those retrofitting them and their occupants. • Retrofit metrics embody values and views about how retrofit should be undertaken.• Unpacking metric design and considering scope, headline measures, normalisation factors and timescale separately can help inform better policy decisions. • There is no one ideal metric for building retrofit-many policies and standards use multiple metrics. • A focus on carbon metrics only for retrofit can lead to missing opportunities for high-quality building fabric. Energy metrics remain important.

The Australian policy approach, based on the NABERS energy performance benchmarking scheme for commercial offices, is promoted as a 'success story' and is of interest to governments internationally. This paper explores the evidence for the impacts of the Australian approach on energy use and carbon emissions, identifies the key elements of its conception, design and implementation, and investigates the role of government. It uses a mixture of literature review, re-analysis of quantitative data and analysis of 30 original stakeholder interviews. The literature suggests that NABERS' appeal to multiple benefits of energy efficiency and its place in the wider policy mix should help deliver positive results. Analysis of publicly available data has highlighted data gaps. However, evidence suggests significant energy savings have been made, although the attribution to NABERS alone, given the policy mix, is uncertain. The interviews show high levels of agreement that the policy mix has transformed large commercial office buildings. They also highlight the wide range of actors mobilised to deliver this change and the central role of well-designed government intervention and support. The Australian experience is rightly of interest to international governments, but they must recognise that replicating its success requires attention to detail and long-term commitment. POLICY RELEVANCEThe decarbonisation of commercial buildings is challenging and many countries, including the UK, are struggling to make progress. In-use performance benchmarking policies such as NABERS are considered to be effective by engaging with industry and promoting the multiple benefits of energy efficiency. The lessons from the Australian experience help to identify four key policy design features for governments to consider: (1) political leadership, adequate financial resources and people with the right engineering and