Retrospective U-value audit

Publication date
24th June 2016
Information types
Policy areas

On 1 June 2016 we introduced a new policy for cavity wall insulation (CWI) measures with overwritten U-values. This new policy gives us additional assurance in the savings attributed to these measures. 

In our consultation response which set out this new policy we also specified our intention to undertake a retrospective desk-based audit of ECO2 CWI measures with overwritten U-values. This will be restricted to measures installed under ECO2 up to the implementation date of our new policy (1 April 2015 - 31 May 2016).

This desk-based audit will look at the evidence retained when overwriting a U-value and be conducted on a statistically significant sample per supplier. The audit will be targeted at measures with a U-value that exceeds the thresholds set out in our response to the U-value consultation.

Once the audit has been completed, we will ask suppliers to rescore measures that failed the audit using the appropriate default U-values, if applicable.

We will also be conducting an audit of measures installed after 31 May 2016 to ensure that the new requirements introduced for CWI measures with overwritten U-values have been implemented correctly. We are still considering how this audit will be conducted and will share further details at a later date.

If you have any questions about this audit please contact the ECO Team at

Update 23 May 2017 - U-values audit summary report

On 24 June 2016 we announced that we would undertake an audit of some cavity wall insulation measures that were installed between 1 April 2015 and 31 May 2016. The audit specifically targeted cavity wall insulation measures that were scored with a bespoke calculated U-value that was different from the SAP default value. This audit was in response to concerns that some U-values were overstated to increase the savings scores for measures.

In addition, we also audited a small number of cavity wall insulation measures installed after 31 May 2016. This audit was to determine whether these measures had been installed in accordance with the updated requirements for cavity wall insulation measures that we published on 1 June 2016.

The report below contains the overall findings of the audit, which was conducted on our behalf by the Energy Savings Trust. Overall, we found limited evidence of manipulation of U-values. We identified a small number of measures with implausible inputs to the U-value calculation, which we have asked suppliers to rescore. On the basis of the audit findings, we decided that no further action was required. All suppliers received individual reports with further details on their own measures.