PAS 2035:2023 Changes

PAS 2035:2023 has been the mandatory standard for domestic retrofit in England, Scotland and Wales since 30 March 2025, when the previous edition – PAS 2035:2019+A1:2022 – was formally withdrawn. This blog covers the key changes from the 2019 edition, and what they mean in practice for anyone delivering retrofit work today.

In this blog, you’ll learn:

• The key changes introduced in PAS 2035:2023
• How the updated standard supports large-scale retrofit projects
• The new requirements for airtightness, ventilation and moisture management
• The evolving role of the Retrofit Coordinator and Main Contractor
• How PAS 2035:2023 aligns with other industry standards and policies

Key Changes in PAS 2035:2023

Here are the key differences between PAS 2035:2019 and PAS 2035:2023:

1. Updated Guidance Clauses

PAS 2035:2023 aligns with national policy and places greater emphasis on consumer protection. Guidance clauses have been refined to provide clearer direction for retrofit professionals, ensuring that projects meet both regulatory and quality assurance standards.

2. Supporting Large-Scale Retrofit

To facilitate large-scale retrofitting, the standard allows design work to begin based on assessments of property archetypes. However, every individual dwelling must still undergo its own retrofit assessment, improvement options evaluation, and Medium-Term Improvement Plan before project completion.

3. Inclusion of BEIS Retrofit Technical Guides

PAS 2035:2023 integrates the BEIS retrofit technical guides, making them a formal reference within the standard. This helps unify best practices and technical methodologies across the industry.

4. Simplified Risk Assessment Process

Under PAS 2035:2019, every project was assigned an aggregate risk grade of A, B or C via a standalone risk assessment annex – Annex B. PAS 2035:2023 removes this: Annex B now covers Industry Quality Assurance Schemes instead, and risk considerations are integrated into the Retrofit Coordinator‘s responsibilities throughout the project lifecycle, rather than assigned as a single classification upfront.

5. Shift to Whole-Dwelling Retrofit

The updated standard reinforces a whole-dwelling approach, moving away from a measures-based retrofit strategy. It introduces a stronger focus on the role of the Main Contractor (where applicable) and clarifies that compliance with PAS 2035 ultimately falls on the PAS Certification holder – whether that is the Main Contractor or the Retrofit Installer.

6. Clarification of the Retrofit Coordinator’s Role

The Retrofit Coordinator’s responsibilities have been expanded, particularly regarding site visits and documenting non-compliance. Their oversight role now spans from project inception to completion, ensuring adherence to PAS 2035.

7. Mandatory Medium-Term Improvement Plans

Unlike PAS 2035:2019, where medium-term improvement plans were framed as recommended good practice rather than a firm requirement, PAS 2035:2023 makes them mandatory for every dwelling. These plans outline a structured roadmap for future energy efficiency improvements beyond the immediate retrofit project.

8. Airtightness Strategy Requirement

Projects must now incorporate an airtightness strategy, including specific targets and testing requirements where applicable; a more structured approach to reducing uncontrolled air leakage.

9. Considerations for Historic Buildings

A new Annex E has been introduced to guide assessments of historic and traditional buildings. This aligns with BS 7913 and ensures that retrofit measures respect the architectural and material integrity of older properties.

10. Simplified Ventilation Requirements (Annex C)

Ventilation requirements have been revised and simplified in PAS 2035:2023 to align with Approved Document F. Functional ventilation testing is now a core requirement, ensuring that systems perform effectively post-retrofit.

11. Strengthened Monitoring and Evaluation

The new standard references BS 40101 for Building Performance Evaluation, emphasising a continuous approach to monitoring and evaluating energy performance from project initiation through to post-completion.

12. Distressed Replacement of Heating Appliances

A new process allows distressed replacement of heating appliances to be retrospectively brought into compliance with PAS 2035, ensuring flexibility while maintaining regulatory standards.

13. Enhanced Climate Resilience and Adaptation

With growing concerns about climate change, PAS 2035:2023 strengthens requirements for assessing overheating risk and ensuring that retrofit measures contribute to long-term climate resilience.

14. Stricter Pre-Installation Building Inspections (PIBI)

The qualifications and requirements for independent inspections of pre-installation building inspections (PIBI) have been reinforced. These inspections must meet the revised PAS 2030 annex requirements.

15. Improved Moisture Management Guidance

Moisture risk management has been updated to align with BS 5250, ensuring that retrofit projects do not inadvertently introduce damp or condensation risks.

What’s Next?

PAS 2035:2023 reflects the evolving needs of the retrofit industry – stronger consumer protection, better support for retrofit at scale, and a genuine whole-dwelling approach in place of a measures-based one. It’s been the mandatory standard for well over a year now (September 2026) , so if a project or supply chain hasn’t fully transitioned, that’s a live compliance gap rather than a future one.

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We carry out PAS 2035:2023-compliant retrofit assessments, coordination and design, and can review an existing project or supply chain against the current standard.