| Summary: | ‘Fabric first’ describes an approach to improving the thermal performance of residential buildings by prioritising the improvement of fabric. It has historically been widely advocated. However, the urgency of complete decarbonisation challenges this approach in existing buildings. Heat decarbonisation is necessary to deliver zero-carbon goals. In many cases, no additional fabric improvement is needed to decarbonise heating; a heat pump, or other zero-carbon heat supply, will be enough. Retrofitting fabric first may not be feasible across the whole housing stock on timescales necessary for rapid decarbonisation and could therefore slow housing decarbonisation. However, fabric improvement will continue to have an important role. Energy use in buildings with a ‘heat pump only’ retrofit will be higher than if insulation were also improved. Fabric should continue to be prioritised in new buildings and where low-cost insulation measures are available. Fabric improvement can have other benefits: lower running costs, improved comfort, reduced damp risk, better heat pump performance, reduced overheating risk and lower requirements for electricity capacity increases. The suitability of a heat-pump-only approach to building decarbonisation should therefore be decided building by building. For national building stocks, complete decarbonisation of heating systems is required, but stock average fabric improvement may be 30–50%.
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