DEEP Report 5.01 Salford Energy House Fabric Performance Testing

Farmer, David; Henshaw, Grant; Tsang, Christopher; Roberts, Benjamin; Fitton, Richard; Swan, Will

Abstract

One of the objectives of the Department for Energy Security and Net Zero (DESNZ) Demonstration of Energy Efficiency Potential (DEEP) Retrofit Project was to investigate the unintended consequences of fabric retrofit. The primary objective of the Energy House DEEP fabric performance tests was to assess the potential benefits of a whole house approach to retrofit against ‘typical’ retrofit practice that follows a piecemeal approach. The research involved in performing a staged whole house fabric retrofit of the Energy House that replicated a piecemeal retrofit. The Energy House’s thermal elements were then adapted to be representative of a retrofit that had been performed following whole house approach retrofit principles. Fabric thermal performance testing took place at each stage of the retrofit process to assess the benefit and unintended consequences of applying retrofit measures individually and in combination.

The primary benefit of a whole house approach to retrofit was found to be the reduction in risk of surface condensation and mould growth at junctions. At the baseline stage, measurements indicated that 75% of the Energy House’s junctions presented a risk. Following the piecemeal approach retrofit, 33% of the junctions were still considered to pose a risk. Despite reducing the risk at most junctions, the piecemeal approach retrofit created a risk at a ground floor junction. Following work to convert the piecemeal retrofit to a whole house approach retrofit, only the eaves was considered at risk. The residual risk present from the baseline stage was attributed to difficulty installing a piecemeal retrofit measure rather than issues with the design of the whole house approach retrofit or the conversion process. The whole house approach retrofit measures underperformed by 5% and external wall insulation (EWI) by 17%. This demonstrates that the whole house approach depends not only on design but also material performance, buildability, and workmanship to ensure its principles are realised in practice.

The whole house approach retrofit reduced the heat transfer coefficient (HTC) of the Energy House by 51% from baseline. However, it was not significantly different to the 50% HTC reduction from baseline achieved by the piecemeal retrofit. A 53% HTC reduction would have been achieved if the whole house approach measures had performed as predicted. As a result, the whole house approach retrofit would not result in significantly lower space heating energy bills than the piecemeal retrofit. Furthermore, the work required to convert the piecemeal retrofit to a whole house retrofit increased the cost of the retrofit by 61%. Although some of the additional cost can be attributed to converting a pre-existing piecemeal retrofit, the additional time and complexity inherent to whole house retrofit means that its additional cost is unlikely to be recouped via payback models that rely on energy bill savings alone. Fabric retrofit funding models must also consider the occupant health as well as energy and carbon reductions.

The EWI system was responsible for 78% of the HTC reduction and removed the risk of surface condensation and mould on the surface of walls and from the greatest number and length of junctions. However, the EWI system did not remedy the significant pre-existing risk along the eaves junction. The whole house approach measure of extending the eaves to link the loft insulation with the EWI was extremely effective at removing the risk, but significantly increases the cost of an EWI installation. The openings did not pose a risk following a piecemeal retrofit, so moving them in line with EWI was unnecessary in this instance. As funding for whole house approach measures through energy saving payback schemes is unlikely to be viable, their application should be targeted according to requirement. Survey tools are required to specify the appropriate whole house approach measures for a retrofit.

Citation

Farmer, D., Henshaw, G., Tsang, C., Roberts, B., Fitton, R., & Swan, W. (2024). DEEP Report 5.01 Salford Energy House Fabric Performance Testing. Department for Energy Security and Net Zero Website: Department for Energy Security and Net Zero

• Report Type: Technical Report
• Acceptance Date: May 15, 2024
• Online Publication Date: Oct 23, 2024
• Publication Date: Oct 23, 2024
• Deposit Date: Nov 21, 2024
• Publicly Available Date: Dec 3, 2024
• Pages: 82
• Keywords: Retrofit, Solid Wall House, Insulation, Energy Efficiency, Building Fabric Performance
• Publisher URL: https://assets.publishing.service.gov.uk/media/6717be32e319b91ef09e3857/5.01_DEEP_Energy_House_Fabric.pdf