Research and analysis

Measures installed under SHDF Wave 2 and HUG 2: Statistical audit results

Published 13 October 2025

Applies to England

This report summarises the results of the randomised samples of audits which were commissioned by DESNZ to understand if non‑compliance was present in the Social Housing Decarbonisation Fund (SHDF) Wave 2 and Home Upgrade Grant Phase 2 (HUG 2).

The results showed that the vast majority of measures (90.3%) do not pose a risk to the fabric of the building, and, or the health of the occupant. A minority of measures (9%) pose a non-immediate risk, and a small percentage (0.7%) pose an immediate risk. All measures audited which posed an immediate risk have been remediated.

Background

In October 2024 Trustmark notified DESNZ that an abnormally high rate of non‑compliance had been detected within ECO4 and GBIS Solid Wall Insulation (SWI) installations. Trustmark shared non‑compliance data on SHDF and HUG in early December 2024.

In December 2024, DESNZ commissioned randomised samples of all measures under SHDF Wave 2 and HUG 2, weighted towards External and Internal Wall Insulation (EWI/IWI), to understand the rate of non‑compliance in the schemes.

The population of un-audited measures installed under SHDF Wave 2.1 and HUG 2 was eligible to be sampled. One sample was drawn for EWI/IWI, a second sample was drawn for all other measures installed under the scheme (all measures excluding EWI/IWI), a third sample was drawn from all measures installed by a Trustmark suspended installer.

The audits were carried out by chartered surveyors against PAS2035 standards.

Results

Table 1 shows the breakdown of results for all measures, as well as the EWI/IWI and all other measures samples.

Severe risks are where the non‑compliance poses a risk to the health and safety of occupants, while high risks are a type of non‑compliance which will undermine the performance of the system, and may over time result in a risk to the health of the occupants. Medium risks are issues that could affect the system performance over time or risk of measure not performing as intended. Low risks are cosmetic or snagging issue with no impact on performance or safety. Please see the annex for comparison of risk ratings with ECO4 and GBIS audits.

For all measures, 0.7% were found to be severe risk, 9% were found to be high risk and therefore 90.3% were found to not pose any risk to health and safety of occupants. For EWI/IWI, 0% were severe risk, 11.7% were high risk and 88.3% were found to not pose any risk to health and safety of occupants. For all other measures, 93.7% were found to not pose any risk to health and safety of occupants, 4.2% were found to be high risk, and 2.1% were found to be severe risk.

Table 1: Rates of non‑compliance found within the sample of audits

	Severe Risk	High Risk	Medium Risk	Low Risk	No Risk
Total	0.7%	9%	30.9%	16.7%	39.9%
Of which: EWI/IWI	0%	11.7%	35.1%	17.6%	35.1%
Of which: other measures	2.1%	4.2%	22.9%	14.6%	49.0%

‘Measures not accessible’ is not included in the table. Audits of the suspended installer are included in the total.

Sampling approach

A randomised sampling methodology was designed based on the total TrustMark lodgement population on 14 December 2024 for SHDF Wave 2.1 and HUG 2 (comprised of 37,947 measures). This approach used a statistically derived sample size. Sampled households were contacted individually by phone, email, or in person at the property.

288 measures were included in the 3 samples. For EWI/IWI, a random statistical sample of 188 was selected from a population of 4,480 measures. This provided a confidence interval of 95% and margin of error of 7%.

For all other measures, a random statistical sample of 96 was selected from a population of 33,463 measures. This provided a confidence interval of 95% and margin of error of 10%.

All 4 lodged measures installed by a suspended installer were audited.   

Replacement properties were carefully selected to mirror the original sample – prioritising the same grant recipient, measure type, and supplier to preserve a similar risk profile. Where that wasn’t possible, a random substitute was used. There were 174 properties replaced through this process.

Conclusions

The audits show there is not a widespread problem of non‑compliance in SHDF Wave 2 and HUG 2.

Annex: Classification of non‑compliance

‘Non‑compliance’ means that a qualified assessor has found that the work carried out does not meet the relevant PAS standard. The scale and seriousness of non‑compliance can vary, as can the amount of work required to put right. The classification of non‑compliance for EWI and IWI for TrustMark and Certification Bodies has been standardised as follows:

Category used in SHDF and HUG audit	Category used in ECO4 and GBIS audit	Classification	Timeline
Severe – Immediate risk to the fabric of the building, and, or the health of the occupant	Major non‑compliance (Category 1)	Category 1 – risk to property or health and safety of occupants identified	Grant Recipient expected to remediate within 24 hours of receiving the report.
High – Non-immediate risk to the fabric of the building, and, or the health of the occupant	Major non‑compliance	High risk of affecting system performance. If not resolved could lead to a Category 1.	Grant Recipient expected to remediate within 12 weeks of receiving the report.
Medium – Risk of the measure failing and or, risk of measure not performing as intended due to installation and or, design	Minor non‑compliance	Medium risk of affecting system performance.	Grant Recipient expected to remediate within 12 weeks of receiving the report.
Low – Cosmetic or snagging issues that don’t affect the performance of the measure, occupant health or building health	Minor non‑compliance	Will not materially affect system performance. Cosmetic/snagging issue with no impact on performance, health or safety.	Expected the be handled at the Grant Recipient’s discretion.
No issues – No issues observes and/or all remediation addressed, and documents align to TrustMark data warehouse	An equivalent is not included as it only has categories for where a non‑compliance is identified	No issue identified	No action required