PAS 2035 explained

What is PAS 2035?

Simply put, PAS 2035 is a framework to follow for the energy retrofit of domestic buildings; that is properties primarily used for living accommodation, like a house, flat, or dwelling).

It details best practice guidance for domestic retrofit projects and delivers a ‘whole- house’ or ‘whole building’ approach which considers:

• Occupants and end users
• Each home individually (including construction)
• Complete oversight of assessment, design, delivery, and use.

This resolves the problems of retrofit measures being considered in isolation, as identified in the government’s ‘Each Home Counts’ review, which may accidently negatively impact building energy efficiency overall.

How will PAS 2035 change your ways of working

Don’t be wrong-footed. Learn the steps in the process of retrofitting a dwelling with energy efficiency (this is set out in the PAS 2035 document standard), which are summarised below.

Step 1. Preliminaries

The first step for all new projects is to set out the client preliminaries – what the client wishes to achieve and the overarching brief for the retrofit project, otherwise known as the Project Intended Outcomes (PIO). This can include items such as improving the EPC rating, increasing resident comfort, and reducing fuel bills. This stage also involves obtaining pre-existing asset data, or pre-construction information from the client.

Step 2. Whole dwelling assessment

This is the first involvement of the Retrofit Assessor, who will be responsible for collating data on the performance of the dwelling and what the proposed performance of the dwelling could be. This is based on the brief provided by the client and delivered to the project team by the Retrofit Coordinator.

This includes items such as understanding the property’s heritage, construction dimensions, current services such as electrical and plumbing, defects, site constraints, U values (thermal performance), moisture control, and suitability for improvement. The assessment also covers occupant appraisal and use of the dwelling, ventilation review, air permeability assessment, fuel consumption and, in the case of a traditional dwelling, a heritage significance statement. The information is assessed to provide an output for improvement under a retrofit design.

Following on from the assessment, the Retrofit Coordinator works with the Retrofit Assessor and Retrofit Designer to provide a medium term retrofit improvement plan (MTIP).

Step 3. Retrofit design

The retrofit design stage takes the assessment and builds this up to a workable construction stage design. This takes an in-depth look at the dwelling performance and what is required to adequately retrofit to avoid any issues and provide a ‘no regrets’ strategy. During this stage, the Retrofit Assessor is retained in case further information is required and the Retrofit Coordinator has full oversight to ensure the design covers the salient points that are raised during the whole dwelling assessment.

Step 4. Installation

Following on from the retrofit design which includes procurement exercises and ensures a warmup introduction for the installer, the Retrofit Coordinator oversees the installation of the retrofit in accordance with PAS 2030:2023. PAS 2030 is the framework and procedure for installation of retrofit measures as opposed to the project management of installation which is PAS 2035.

Step 5. Testing and commissioning

The testing and commissioning period is the responsibility of the Retrofit Installer, however, the Retrofit Coordinator oversees the testing of all installed measures by the Retrofit Installer and ensures that adequate certification and commissioning data is provided as part of this process.

Step 6. Handover

The handover process is much the same as the process for general contract administrator and employer’s agent roles. The Retrofit Coordinator ensures that full health and safety files and O&M instructions are handed over to the client and end-user for an understanding of use of the dwelling and ongoing maintenance. During this period new energy performance certificates and other relevant data is also recorded with TrustMark (or similar) for future information on retrofit, these files being accessible to the client.

Step 7. Retrofit advice

The retrofit advice stage is not just specific to this stage as retrofit advice is provided throughout the project. However, the retrofit advice stage is for the end-user to fully understand the installation that is taking place. It is an opportunity for the Retrofit Coordinator to provide clear, concise and layman’s term knowledge to the end-user – ensuring there are no issues being created with a lack of communication or information from the installer – enabling the occupant to get the most out of the building.

Step 8. Monitoring and evaluation

The monitoring and evaluation stage collates data from the end-user. Firstly, it ensures the retrofit project has been a success and is working within the parameters of both the assessment and the design as expected, and secondly it ensures that the advice provided is being followed by the occupant.

There are several monitoring and evaluation techniques that range from simple survey data, in-depth intrusive data gathering, to inspections, opening up, and monitoring of controls.

Step 9. Claims of compliance

Claims of compliance is a specific step at the end of the monitoring and evaluation stage where all the data for the retrofit installation, design, assessment, and use is gathered and passed along to the quality assurance body.

There are three main routes of claims of compliance:

• Independent third-party certification from a UKAS-accredited body
• Other party validation (where a third-party body is appointed)
• Self-assessment (where the Retrofit Coordinator uploads evidence of compliance in accordance with PAS 2035).

Step 10. Qualifications

Qualifications are covered throughout the document, however, has a specific section at the end of PAS 2035. It covers any conflict of interest and assurance that each retrofit role is fulfilled by an adequately qualified, competent person.

Who’s who in the world of retrofit

The main professional roles for PAS 2035 are:

The Retrofit Assessor

The Retrofit Assessor provides an in-depth assessment of the current arrangement and build of the property and how it may be improved using collated data from several different outlets including surveys and inspections.

The Retrofit Assessor

The Retrofit Assessor provides an in-depth assessment of the current arrangement and build of the property and how it may be improved using collated data from several different outlets including surveys and visits.

The Retrofit Coordinator

This is an end-to-end role with full responsibility for demonstrating compliance with PAS 2035 and full oversight of both the installation and handover phases, working alongside the installer.

The Retrofit Designer

The Retrofit Designer develops the assessment and the medium-term improvement plan to provide a fully compliant retrofit design. This is also overseen by the Retrofit Coordinator to ensure that the requirements of the intended outcomes and whole dwelling assessment are both met.

The Retrofit Installer

The Retrofit Installer is a contractor who installs the retrofit measures specified in accordance with PAS 2030.

The Retrofit Evaluator

The Retrofit Evaluator carries out monitoring and evaluations post installation of the retrofit. This can include data gathering or can be in-depth analysis using a number of control monitors and intrusive survey works.

Is it mandatory?

PAS 2035 is not mandatory for all retrofits, but since 20 June 2021, PAS 2035 compliance has been a requirement for any publicly funded retrofit projects. PAS 2035:2023 is the 2023 version of the standard which came into full effect on 30 March 2025.

Although it is not strictly needed for non-funded projects, it is recommended that the framework is used for any residential retrofit projects as it provides a clear path to compliance and best practice for the assessment, design, installation and monitoring of energy efficient measures.

What’s changed from the 2023 version?

PAS 2035:2023 brought key updates focusing on whole-dwelling retrofit, streamlining processes, clarifying roles, and strengthening technical requirements, notably removing risk pathways for simplification, adding requirements for airtightness strategies, enhancing occupant engagement, incorporating climate resilience, and clarifying the distinct roles of Retrofit Designer and Retrofit Coordinator, and removing the separate role of Retrofit Advisor.

Next steps

Now you’re up to speed, please get in touch to find out how we can help your projects. We have a dedicated, experienced team who can help put PAS 2035 into practice.