The Department and TrustMark told us that TrustMark would oversee a find-and-fix process for homes with external wall insulation. It would offer audits to all homes with external wall insulation installed through ECO4 or GBIS, provide direct oversight to ensure the work is corrected, and work with local communities to build engagement and trust.31 TrustMark and the Department expected, at the time we took evidence in November 2025, all relevant homes to have been audited (providing access is granted) within 23 Q 82 24 C&AG’s Report, para 2.27 25 C&AG’s Report, Figure 10 26 This is based on the midpoint of the estimated range of 32,000 to 35,000. 2,934 / 33,500 = 9%. 27 Letter from the Department of Energy Security & Net Zero, dated 2 December 2025 28 C&AG’s Report, Figures 6 and 10 29 Qq 1, 75, 153; C&AG’s Report, para 2.19 and Figure 6; Energy Security and Net Zero Committee Oral evidence: Retrofitting homes for net zero, HC 453, 12 February 2025 30 Qq 70, 133-137 31 Qq 57, 61 ,76, 139, 151; Letter from TrustMark, dated 25 November 2025; The Department has provided more information on the audit process, including who is eligible and contact information, at: www.gov.uk/insulation-check 13 12 to 15 months.32 The Department told us that any defects identified should be fixed by installers within 12 weeks, although it accepted that this may take longer when the guarantee needs to be invoked. The Department said that “a lot of this” would be resolved within 18 months.33 In written evidence submitted to us after the oral evidence session, TrustMark estimated there were around 20,000 homes with faulty external wall insulation yet to be found and fixed.34 We believe this timescale is very optimistic which is one of the reasons we have recommended that the Department gives the Committee regularly six monthly updates on this matter.