As of 31st March 2025, PAS 2035:2023 became the required standard for all retrofit projects registered from that date onwards. Now that it’s been in use for a few months, it’s a good time to take another look at the differences between the new 2023 edition and the previous 2019 version.
Why was the standard updated?
Standards are regularly reviewed and updated to ensure they remain fit for purpose. This is especially important when government funding is tied to compliance, as is the case with PAS 2035. It’s essential that those working in the retrofit sector understand the changes and take the necessary steps to comply, helping to reduce the risk of funding issues further down the line.
As always, we strongly recommend reading the full document and using this summary to support your understanding. It’s important to read clauses in context rather than in isolation, as the document can be complex. Below, we’ve highlighted some of the key updates:
Key Process Changes
- The Risk Path procedure has been removed. As a result, changes have been made (such as to Retrofit Designer qualification requirements) based on the number of measures being installed and other relevant factors. (See later comments for more detail.)
- The definition of Traditional Construction has been updated and expanded (see page 5).
- A medium-term improvement plan is now required for all properties (clauses 5.3.1 and 8.1).
- The scope of the standard now includes distressed replacements of heating appliances (clause 7.2).
- Where appropriate, the Retrofit Assessor’s report must now cover additional issues that could impact the project in the short or long term (clause 7.3.2.I).
- The design criteria for airtightness and leakage strategy has been revised. If EEMs (Energy Efficiency Measures) improve the building fabric, a strategy must be included. If an airtightness target is set, a test must be carried out to prove compliance. However, setting a target is optional (clauses 8.2.35 and 8.2.36).
- If the Retrofit Designer identifies issues with the improvement option evaluation or the medium-term plan, these must be addressed and updated by the end of the design process (clause 8.2.38).
- The Retrofit Coordinator must collect evidence confirming that the installation of EEMs has been completed correctly. This can be done via in-person or remote/virtual site inspections, or by a third party if necessary. However, where any measure listed in clause 9.2 connects to or penetrates another fabric measure being installed (or already installed), an in-person inspection by the Coordinator is mandatory.
- A written record of all inspections must be kept, along with photographic evidence (clause 9.3.1).
- Guidance on retrofit at scale has also been updated (clause 5.4).
- PAS 2035 (2023) now includes a more detailed explanation with respects to significance assessments for building with aspects of significance, as well as a predefined survey checklist.
