PAS 2035: – What’s Changing and What It Means for Retrofit in the UK

TL;DR: PAS 2035: introduces key updates for UK retrofit projects, including the removal of the risk pathway process, expanded traditional construction definitions, mandatory medium-term improvement plans, stricter ventilation and airtightness requirements, and enhanced qualifications for Retrofit Designers. These changes take effect for properties submitted to TrustMark after 30th March 2025. Professionals should start adapting now to ensure compliance and maintain project efficiency.

In September 2023, PAS 2035 was updated with several significant changes that will impact the way retrofit projects are planned and executed across the UK. These changes are set to take effect for any properties submitted to TrustMark after 30th March 2025, meaning industry professionals must begin adapting their processes now to stay compliant.

This article breaks down the key changes, what they mean for retrofit professionals, and how they will shape the future of energy efficiency improvements in the UK.

Key Changes in PAS 2035:2023

1. Removal of the Risk Pathway Process

Previously, retrofit projects were classified into three risk pathways (A, B, and C) based on complexity. This has now been removed, and all properties will be treated as Path B, with additional requirements for high-risk properties, such as pre-1919 buildings or system-built properties. For pre-1919 buildings, Level 3 Historic Building qualifications will now be required for Retrofit Assessors, Retrofit Coordinators, and Retrofit Designers.

2. Expanded Definition of Traditional Construction

The definition of Traditional Construction has been updated and expanded. Now, solid brick, stone, or earth external walls built with moisture-permeable materials (pre-1919) are considered traditional. Additionally, pre-1919 timber frame structures with any type of infill are included, regardless of their listed status or conservation area location.

3. Medium-Term Improvement Plans Now Mandatory

A medium-term improvement plan is now required for all properties, ensuring retrofit strategies consider long-term sustainability rather than just immediate upgrades.

4. New Provisions for Distressed Heating System Replacements

PAS 2035:2023 now includes guidance on emergency (distressed) heating system replacements, allowing for a smoother integration of energy-efficient heating solutions in urgent situations.

5. Updates to Retrofit Assessments & Condition Reports

• Retrofit Assessor reports must now include more detailed ventilation assessments.

• SAP 10 calculations will become standard, bringing assessment methodologies closer to Full SAP (including air permeability and ventilation factors). SAP 10 is set to be released in March/April 2024.

• The Retrofit Coordinator must now collect more robust evidence to confirm that Energy Efficiency Measures (EEMs) have been installed correctly. This includes in-person or remote site inspections, with photographic evidence required for TrustMark submissions.

  
  

6. Changes to Airtightness & Ventilation Requirements

• If EEMs improve the building fabric, a specific airtightness strategy must be in place.

• If an airtightness target is set, compliance must be proven with testing (though a target is not mandatory).

• Ventilation requirements must now align with updated UK Building Regulations, rather than previous PAS 2035 guidelines.

  
  

7. Retrofit at Scale – New Guidance

The new version includes revised guidance for large-scale retrofit projects, making it easier to apply best practices across multiple properties at once.

8. Retrofit Design – New Qualification Requirements

• Retrofit Designers must now hold a suitable qualification, and Retrofit Coordinators can no longer act as designers as they previously could under Pathways A & B.

• Responsibility for the design process rests solely with the specialist designer, improving accountability and expertise in retrofit solutions.

  
  

9. Post-Evaluation Now Required

A new requirement for post-retrofit evaluation has been introduced. This means:

• A post-evaluation questionnaire must be sent to residents within three months of project completion.

• Retrofit Coordinators must maintain written records of inspections, along with photographic evidence.

What These Changes Mean for Retrofit Professionals

These updates represent a major shift in the way retrofit projects are delivered in the UK. Here’s what they mean for different industry professionals:

• Retrofit Coordinators – Will need to take a more hands-on role in collecting compliance evidence, conducting post-evaluation assessments, and working closely with designers.

• Retrofit Assessors – Must now provide more in-depth reports, especially in areas of ventilation and airtightness.

• Retrofit Designers – Will need to meet higher qualification standards and take full responsibility for energy efficiency design.

• Installers & Contractors – Will need to ensure that all airtightness, ventilation, and medium-term improvement plans are implemented correctly to meet compliance requirements.

  
  

How to Prepare for PAS 2035:2023 Changes

Since these changes take effect for any property submitted to TrustMark after 30th March 2025, professionals in the industry should start adjusting their workflows now. Key actions include:

• Reviewing qualification requirements – Ensure that relevant team members meet the new qualification standards, particularly for Retrofit Design and Historic Building expertise.

• Updating assessment methodologies – Make necessary adjustments to assessments and reports to comply with expanded ventilation, airtightness, and condition report requirements.

• Enhancing compliance documentation – Ensure robust evidence collection for inspections, including photographic records, written documentation, and resident feedback surveys.

• Aligning projects with new ventilation regulations – Start following updated UK Building Regulations rather than older PAS 2035 guidance.

  
  

Conclusion

PAS 2035:2023 introduces major changes that will affect how retrofit projects are carried out in the UK. With a stronger focus on whole-building solutions, long-term improvement planning, and stricter compliance measures, professionals must take proactive steps to ensure their projects align with these new standards.

At Target Green, we are committed to staying ahead of these changes and delivering high-quality, compliant retrofit solutions. If you need guidance on how PAS 2035:2023 affects your projects, get in touch with us today.