At midnight on 30th March 2025, the PAS 2035:2019 standards were officially withdrawn and replaced by the updated PAS 2035:2023 standards. Published by the British Standards Institution (BSI) in September 2023, this revised edition now defines the retrofit compliance framework for all Government-funded projects in the UK.
This marks a major shift for the industry, with 15 revisions introduced to support higher quality, whole-dwelling retrofit and to align with evolving policy, climate goals, and consumer protections.
Let’s explore the key changes and what they mean in practice.
What Is PAS 2035?
PAS 2035 is the UK’s overarching retrofit standard for domestic buildings. It provides a structured, quality-assured framework for improving energy efficiency, moving beyond individual measures to deliver a holistic ‘whole-house’ approach. It guides the assessment, design, coordination, installation, and monitoring of retrofit works, ensuring long-term performance and occupant well-being.
As of March 2025, PAS 2035:2023 is mandatory for all Government-funded retrofit schemes. All professionals involved must now comply with the updated version to continue delivering compliant projects.
Key Updates in PAS 2035:2023
1. Updated Guidance Aligned with Policy & Consumer Protection
The revised clauses now:
- Reflect national net zero and housing policy.
- Place greater emphasis on consumer protection, project quality, and performance monitoring.
2. Support for Large-Scale Retrofit
Retrofit Design can now begin based on archetype assessments, supporting scalability. However, each property must still receive its own Retrofit Assessment, Improvement Options Evaluation and Medium-Term Improvement Plan before completion.
3. Integration of BEIS Technical Guides
The BEIS Retrofit Technical Guides are now formal references within the standard, helping unify best practice across design, installation, and coordination.
4. Simplified Risk Assessment
The complex “Risk Pathway” procedure from PAS 2035:2019 has been removed. Instead, risk assessment responsibilities are integrated throughout the Retrofit Coordinator’s role and project lifecycle.
5. Shift Toward Whole-Dwelling Retrofit
The 2023 update reinforces a whole-dwelling approach, moving away from the measures-based retrofit pathway. It introduces a stronger focus on the Main Contractor (where applicable), and clarifies that overall compliance lies with the PAS Certification Holder, whether that’s the Contractor or Retrofit Installer.
6. Expanded Retrofit Coordinator Role
The Retrofit Coordinator’s duties now span:
- Site visits (mandatory in some scenarios).
- Recording and managing non-compliance.
- Oversight from project inception through to completion.
7. Mandatory Medium-Term Improvement Plans
Previously optional, the Medium-Term Improvement Plan (MTIP) is now required for all properties. This ensures retrofit projects include a clear roadmap for future improvements.
8. Airtightness Strategy Requirement
A structured airtightness strategy is now essential when energy efficiency measures affect the building fabric. Projects may need to set a specific airtightness target and verify it with testing.
9. Guidance for Historic and Traditional Buildings
New guidance (Annex E) has been added to help retrofit professionals assess and plan improvements to older or traditionally constructed buildings, especially those with historical or architectural importance. It builds on the principles of BS 7913 (the standard for conserving historic buildings) to ensure that retrofits are sensitive, appropriate, and don’t harm the building’s character or fabric.
10. Simplified Ventilation Requirements
The rules around ventilation have been updated and made easier to follow. These updates (set out in Annex C) bring PAS 2035 in line with the Building Regulations, Approved Document F – Ventilation. One key change is that ventilation systems now need to be tested to make sure they’re working effectively, this functional testing is now a required part of the process.
11. Monitoring and Evaluation Requirements
A renewed focus on monitoring and evaluation is introduced, referencing BS 40101. Performance must now be considered from project inception through to completion.
12. Distressed Heating Appliance Replacement
A new process allows for distressed replacements (e.g. broken boilers) to retrospectively comply with PAS 2035, improving flexibility without compromising standards.
13. Enhanced Climate Resilience Guidance
The updated PAS provides stronger guidance on climate adaptation and resilience, supporting long-term sustainability in the face of changing weather patterns.
14. Improved Inspection Requirements
Pre-installation Building Inspections (PIBIs) now require independent inspection and improved competency, as defined in updated PAS 2030 annexes.
15. Alignment with BS 5250:2021
Requirements related to moisture risk and control are now aligned with BS 5250:2021, offering clearer guidance for tackling damp and condensation in retrofit.
Why PAS 2035:2023 Compliance Matters
With the 2019 version now withdrawn, compliance with PAS 2035:2023 is mandatory for any Government-funded retrofit activity. Beyond meeting funding criteria, it helps ensure:
- High quality, risk-managed retrofit projects
- Improved energy performance and building durability
- Better occupant health, comfort, and satisfaction
- Futureproofing homes for climate, energy, and policy change
Summary
PAS 2035:2023 represents a leap forward in the UK’s approach to retrofitting. By streamlining processes, reinforcing whole-dwelling design, and integrating best-practice guidance, it sets a new standard for quality and accountability in the sector.
Understanding and applying the updated PAS 2035 is now essential for staying compliant and delivering meaningful, lasting improvements to homes across the UK.
If you need guidance on how to deliver projects in line with PAS 2035:2023, or want to review your current approach, our team is here to help.
You can view the full PAS 2035/2030 standard on the official BSI website:
