Look no further if you need to understand what the retrofit remediation crisis means for your organisation. The latest evidence is clear: poor-quality insulation has created a significant compliance, financial and reputational risk for landlords, social housing providers, councils and installers.

A National Audit Office report found that 98% of homes with external wall insulation installed under ECO4 and the Great British Insulation Scheme required remediation. The government has acknowledged that widespread failures were linked to weaknesses in scheme design, oversight, competence and quality assurance.

Now, TrustMark has tightened the rules. For ECO4 and GBIS measures inspected on or after 1 June 2026, TrustMark no longer accepts requests to extend the standard eight-week remediation period. Where deadlines have passed without compliant remediation and evidence, the consequences can include a voided Certificate of Lodgement and referral to Ofgem.

This is not simply an installer problem. It is a whole-property and asset-management issue. The question for landlords and social housing providers is no longer whether a property was treated. It is whether the work was properly assessed, designed, installed, monitored, evidenced and integrated into the building.

The scale of the retrofit remediation crisis

The National Audit Office report identified serious failures in the quality of insulation delivered through ECO4. The government’s subsequent consumer protection consultation confirmed that:

• 98% of external wall insulation installations reviewed required major remediation.
• 29% of internal wall insulation installations reviewed required major remediation.
• Some issues created risks of damp, mould, poor thermal performance and damage to the building fabric.
• Oversight was fragmented, with unclear accountability between suppliers, installers, certification bodies and retrofit professionals.

Thousands of homes have since entered audit and remediation programmes. However, progress has been slow, and the challenge is becoming more urgent as ECO4 reaches its final stages.

TrustMark’s current Quality Assurance guidance confirms that the standard remediation period for ECO4 and GBIS is eight weeks from notification of non-compliance. For measures inspected from 1 June 2026 onwards, there is no longer an extension route.

That creates a hard operational deadline for organisations managing affected properties.

What the closed remediation window means in practice

The closed window does not mean that a defective installation becomes acceptable. Nor does it necessarily remove the installer’s contractual, scheme or guarantee obligations.

It means that the formal opportunity to request additional time through TrustMark has closed for the relevant inspections. If remediation is not completed and evidenced within the required period:

1. The installation may remain recorded as non-compliant.
2. The Certificate of Lodgement may be voided.
3. The matter may be referred to Ofgem.
4. The installer or Retrofit Coordinator may face further compliance action.
5. The property owner may need to arrange urgent technical investigation and corrective works.
6. The landlord or asset manager may still carry the ongoing responsibility for managing risks to residents and the building.

This distinction is essential. The installer’s remediation obligation concerns putting defective work right, usually at the responsible party’s cost. The owner’s ongoing liability concerns the property itself: resident safety, damp and mould risk, asset condition, statutory duties, insurance, future maintenance and energy-performance obligations.

Where a contractor has ceased trading, disengaged or failed to complete the work, the owner cannot simply ignore the issue because the original installer was responsible. You may need to invoke guarantees, engage an alternative competent installer, secure independent evidence and demonstrate that proportionate action has been taken.

The government’s ECO4 extension decision makes clear that the extension was intended partly to give suppliers and installers more time to remediate non-compliant installations. That time must now be managed carefully.

Why PAS 2035 compliance is the strongest defence

PAS 2035 compliance is not a box-ticking exercise. Properly applied, it provides a structured audit trail showing how the property was assessed, why measures were selected, how risks were managed and how the completed work was evaluated.

The standard supports a whole-house approach involving:

• A detailed property condition assessment.
• Assessment of existing ventilation and moisture risks.
• Consideration of occupancy and heating patterns.
• Identification of interactions between insulation, heating, ventilation and airtightness.
• A risk-based improvement plan.
• Appropriate design and sequencing.
• Retrofit Coordinator oversight.
• Installation evidence and post-installation evaluation.

This is why PAS 2035 can be such an important defence when quality or performance is challenged. It demonstrates that decisions were based on property-specific evidence rather than a generic measure-led approach.

However, compliance must be genuine and supported by records. A PAS 2035 project with incomplete surveys, weak design information, missing photographs or no evidence of site oversight will be difficult to defend.

Insulation failure is rarely just a fitting problem

From our 15+ years of real-world installer and retrofit experience, we know that insulation failure is often caused by a combination of issues rather than one isolated workmanship defect.

Common causes include:

• Insulation installed over defective or wet substrates.
• Inadequate detailing around windows, doors, eaves and plinths.
• Poor consideration of rainwater penetration and exposure.
• Ventilation reduced without a suitable replacement strategy.
• Measures installed in the wrong sequence.
• Existing defects concealed rather than repaired.
• Incompatible materials or poorly coordinated interfaces.
• No meaningful post-installation inspection.

A technically competent installer can still be placed in an impossible position if the design is incomplete, the substrate has not been assessed or the programme prioritises speed over sequencing.

Why whole house retrofit matters

A home is a system. Improving one element changes the performance of the others.

For example, adding external wall insulation may improve thermal performance and reduce heat loss. But if the work changes airtightness without addressing ventilation, indoor humidity can increase. If window reveals, roof junctions or rainwater goods are not properly detailed, water ingress may follow. If heating controls are not reviewed, the expected energy savings may not be achieved.

A whole house retrofit approach considers the relationship between:

• The building fabric.
• Heating and hot water.
• Ventilation.
• Airtightness.
• Moisture movement.
• Occupancy.
• Existing defects.
• Future improvement measures.

This is also why air pressure testing can be valuable. Properly planned testing can help identify air leakage, support performance analysis and provide evidence about the building before and after improvement. It must be completed by suitably trained personnel using calibrated equipment and the correct methodology.

What the Warm Homes Plan 2026 must learn

The failures under ECO4 and GBIS are already shaping the emerging consumer protection model for the Warm Homes Plan 2026.

The government’s 2026 consultation proposes a more integrated system, potentially overseen by the Warm Homes Agency. Proposals include:

• Centralised oversight of government-supported retrofit.
• Risk-based auditing and inspection.
• Better data sharing across schemes and certification bodies.
• Clearer competence requirements.
• Stronger installer accountability.
• Central case management for complaints and remediation.
• More robust financial protection and redress.

The proposed Warm Homes Agency compliance regime is not yet a substitute for current responsibilities. It is a warning about the direction of travel: future programmes are likely to demand clearer evidence, more reliable data and stronger accountability from every participant in the supply chain.

The current skills gap makes this more challenging. Training capacity has historically been weighted towards new-build construction, while the retrofit market needs more people who understand diagnostics, existing building defects, moisture, ventilation and complex sequencing.

The EPC C by 2030 pressure is increasing

The remediation crisis arrives as landlords face growing pressure to meet EPC C by 2030.

Recent sector analysis of the social housing MEES challenge has highlighted a potential bill of approximately £16 billion, alongside major delivery risks around finance, supply-chain capacity and workforce skills. You can read related sector context in this analysis of the social housing MEES challenge.

For landlords, social housing providers and councils, the answer cannot be to accelerate low-quality installations simply to improve EPC scores. A defective measure may create future costs that outweigh its short-term benefit.

The priority must be compliant, durable and properly evidenced improvement.

A practical compliance checklist

Whether you are a landlord, council, social housing provider or installer, we recommend taking the following steps:

1. Identify affected properties
   Review ECO4 and GBIS records, particularly external and internal wall insulation projects.

2. Check every remediation deadline
   Establish when non-compliance was notified, whether the eight-week period has expired and whether the inspection took place on or after 1 June 2026.

3. Secure the complete project file
   Gather assessments, designs, risk-path documents, photographs, ventilation information, installation records, guarantees and TrustMark correspondence.

4. Arrange an independent technical review
   Do not rely solely on a contractor’s own assessment where liability or compliance is disputed.

5. Investigate the whole building
   Check moisture, ventilation, thermal bridges, airtightness, detailing and adjacent measures, not just the visible insulation finish.

6. Use a competent Retrofit Coordinator
   Ensure the project is reviewed against PAS 2035 principles and that the proposed solution is properly designed and sequenced.

7. Plan remediation with evidence in mind
   Agree the scope, method, materials, photographs, video evidence, inspection points and sign-off requirements before works begin.

8. Escalate unresolved cases promptly
   Engage the guarantee provider, TrustMark, Ofgem or relevant certification body where the installer has failed to act.

9. Strengthen future assurance
   Use independent C3 Technical Monitoring, site inspections and post-installation checks to identify problems before they become systemic.

10. Link remediation to your stock strategy
    Use the findings to inform your EPC C by 2030 programme, planned maintenance budgets and wider social housing retrofit plans.

How CPH Retrofit can support you

At CPH Retrofit, we combine more than 15 years of practical experience, including experience as retrofit installers, with specialist knowledge of PAS 2035 compliance, coordination and technical monitoring.

Our work spans London, Tyneside, Yorkshire and Norfolk. We understand the pressures faced by national contractors, ECO installers, councils, housing associations and social landlords because we have worked across large and complex domestic retrofit programmes.

We can support you with:

• Retrofit remediation services.
• Independent technical investigations.
• PAS 2035 compliance reviews.
• Retrofit assessment and whole-house planning.
• Retrofit Coordinator services.
• C3 Technical Monitoring and compliance audits.
• Ventilation reviews and air pressure testing.
• Evidence preparation for audits, remediation and sign-off.
• Retrofit measure modelling to identify the best-value route to compliance.

Frequently asked questions

Does the end of the TrustMark extension route remove an installer’s responsibility?

No. The closed extension route affects the formal TrustMark remediation timetable. It does not automatically remove contractual, scheme, guarantee or other responsibilities. Specialist advice should be obtained for individual cases.

What happens if the original installer is no longer trading?

You should review the relevant guarantee and financial protection arrangements, notify the appropriate scheme or oversight body and obtain an independent technical assessment. An alternative competent installer may be required.

Is PAS 2035 compliance a complete legal defence?

No. PAS 2035 compliance is not a guarantee that a project cannot be challenged. However, a properly documented PAS 2035 process provides strong evidence that risks were assessed, measures were coordinated and responsibilities were managed correctly.

Can insulation be remediated without reviewing ventilation?

Sometimes, but it is rarely good practice to consider insulation in isolation. Ventilation, moisture and airtightness should be assessed as part of a whole-house review.

Why is C3 Technical Monitoring now important?

C3 Technical Monitoring provides independent quality assurance through desktop reviews and on-site inspections. It helps identify recurring issues, verify installation quality and demonstrate that your quality management system is operating effectively.

Act before a closed deadline becomes an open liability

The 98% remediation figure is a serious warning for the retrofit sector. The lesson is not to avoid insulation. It is to deliver retrofit properly: assess the building, design for the whole house, coordinate the measures, monitor the work and retain clear evidence.

If you are responsible for affected properties, do not wait for a further audit, complaint or EPC deadline to expose the problem.

Book a retrofit assessment, or speak to our team about retrofit remediation services, PAS 2035 compliance and C3 Technical Monitoring.