DESNZ Demonstration of Energy Efficiency Potential (DEEP)
Whole-house Fabric Retrofit
The research compared piecemeal and whole-house fabric retrofit approaches. A staged retrofit of the Energy House was undertaken, with fabric thermal performance measured throughout the programme. This enabled the impact of individual and combined retrofit measures to be assessed.
Both retrofit approaches achieved an approximately 50% reduction in HTC (whole-house heat loss). External wall insulation (EWI) accounted for 78% of the total reduction and was more effective than any other measure at reducing surface condensation and mould growth risk.
Whole-house approach retrofit measures, including extending the eaves to ensure continuity between loft insulation and EWI, delivered only modest additional HTC reductions. However, these measures significantly reduced the risk of surface condensation and mould growth at junctions.
The findings demonstrate the benefits of the whole-house retrofit approach embodied within PAS 2035. However, the additional investment is unlikely to be recovered through payback models based solely on energy bill savings.