A major new retrofit project has found that Green Deal SAP calculations over-predicted energy savings by an average of 77%.

The FutureFit project was carried out by social home provider Affinity Sutton in order to assess the role that retrofitted energy efficiency measures can play in reducing fuel poverty.

The report monitored 150 different properties across the country which Affinity Sutton identified as falling into 22 common types of housing, representative of around 75% of England’s total housing stock. .

The project identified that whilst there remained challenges in tracking energy use, retrofitting did result in energy savings. However, the social housing provider has ruled out supporting the Green Deal due to major concerns over the Standard Assessment Procedure (SAP) method for energy modelling.

Jeremy Kape, director at Affinity Sutton explained: “The actual savings often differed significantly from what the SAP model predicted. In three out of four cases SAP over-predicted the savings.”

He continued: “Reasons for this were wide-ranging and included overestimating the household’s existing energy use, which suggests that social tenants are likely to be under-heating their homes. Although there have been updates to SAP since FutureFit and in-use factors are applied to the Green Deal assessment, these do not account for the scale of the difference. We welcome the role of the Occupancy Assessment in the Green Deal to try to further address this issue of variance. However, this evidence supports our concern that the Green Deal may still not realise the savings necessary for it to work for our residents. Furthermore the results suggest that for the impacts of retrofit to be equitable, social households must have access to the Affordable Warmth element of ECO.”

The findings cast serious doubt over the veracity of the ‘golden rule’ calculation in the Green Deal – the cornerstone of the scheme. Affinity Sutton calculated that if a weighted average was applied across its electrically-heated properties to gas-heated properties, only 24% would realise their predicted SAP savings.     

Keith Exford, Affinity Sutton CEO, concluded: “The FutureFit project demonstrates how the social housing sector is well positioned to deliver wide-scale retrofit. Although the results make it clear why Affinity Sutton is not currently supporting the Green Deal in our homes, this report sets out why it is so important to find a way to make it work for the very people who need it most.”

The full report can be viewed here.