PAS 2035 is the UK’s retrofit standard framework: the best-practice process for how a domestic retrofit project should be assessed, designed, coordinated and installed, from first survey through to completion. The current version, PAS 2035:2023, has been mandatory for retrofit work delivered under government-funded schemes since 30 March 2025, replacing the earlier PAS 2035:2019+A1:2022. This piece covers what the standard is, where it came from and who’s involved in a compliant retrofit under it.
In this blog you’ll learn:
- What PAS 2035 actually covers, and why it exists
- The Each Home Counts review that created it
- Where the standard applies
- The full retrofit process, from coordination through to handover and evaluation
- What changed in risk assessment under PAS 2035:2023
- The roles involved in a compliant retrofit, and what each one does
What is PAS 2035?
Most of the UK’s existing housing stock needs deep retrofit, not just top-up measures, to meet net zero targets – this is a comprehensive whole-house retrofit, assessed and coordinated to a consistent standard, rather than loft insulation added in isolation. PAS 2035 is the framework that governs how that’s done properly.
The PAS 2035 framework was initially developed as part of the Each Home Counts process. It sets clear guidelines for retrofit professionals to follow when carrying out any domestic retrofit work.
The Each Home Counts review was established to tackle the high levels of failure present in domestic retrofit, and to improve the process for retrofitting energy efficiency and renewable energy measures. As a result of this review, PAS 2035 was established as the standards framework document for the end-to-end delivery of domestic retrofit work.
This framework takes a whole-building approach to the retrofit process. Rather than retrofit work being considered in isolation – which can unintentionally damage the overall building performance – the approach looks at the home, environment, occupancy, and householders’ improvement objectives when determining suitable measures to install.
Overall, the process introduced by PAS 2035 is designed to improve the quality of retrofit work for domestic properties, ensuring that funding from banks and lenders goes towards good quality work that actually improves the energy efficiency of housing.
Each Home Counts
The Each Home Counts review laid out some organisational structures that would be put in place to deliver the core components of the new framework:
- A Quality Mark: all those engaged in the design and installation of energy efficiency and renewable energy will be assessed and certified against this standard – TrustMark.
- A Consumer Charter: this sets out the positive experience that the consumer can expect under the quality mark, including response times, financial protections, and access to redress procedures when things go wrong.
- A Code of Conduct: to set out clear requirements and guidance on how companies operate and report, in order to be awarded and hold the quality mark.
- Technical Codes of Practice and Standards: to minimise the risk of poor-quality installation of home renewable energy and energy efficiency measures.
- An Information Hub and Data Warehouse: a storage facility for information on a property.
Where Does PAS 2035 Apply?
PAS 2035 may be applied to all domestic retrofit activity covered in the following categories:
- Retrofit prompted or funded by national or local government schemes, like the Warm Homes: Local Grant or Optimised Retrofit Programme.
- Retrofit prompted or funded by landlords, including social housing organisations, private landlords in the domestic sector, and property portfolio holders.
- Retrofit of individual buildings by their owners and/or occupants, including both domestic and owner-occupiers.
- Retrofit that is integrated with and forms part of broader repairs, maintenance, and improvements (RMI) activity related to individual buildings or building stocks.
What are the Roles Within the Retrofit Process?
- Retrofit Advisor: competent in giving advice to clients and householders, in accordance with PAS 2035.
- Retrofit Assessor: qualified to carry out a retrofit assessment.
- Retrofit Coordinator: qualified as a specialist retrofit project manager, taking overall responsibility for all elements of the retrofit process.
- Retrofit Designer: qualified to prepare a retrofit design.
- Retrofit Installer: the person or organisation undertaking the energy efficiency measures in an existing building, in accordance with PAS 2030.
What is the PAS 2035 Retrofit Process?
- Coordination. The Retrofit Coordinator confirms the project’s accountability and establishes the intended outcomes with the client at the outset (Clause 6), manages the project’s TrustMark lodgement administration throughout, and holds continuous oversight of risk across every later stage – including post-installation site visits to verify works match the design intent – rather than assigning a single risk grade upfront (see below for what changed here specifically).
- Assessment. A Retrofit Assessor carries out the whole-dwelling assessment – gathering condition, energy performance and occupancy data (Clause 7). On large-scale schemes, PAS 2035:2023 allows design work to begin from validated property archetypes rather than waiting on every individual assessment, though every dwelling must still receive its own assessment before completion.
- Improvement Options Evaluation and Medium-Term Improvement Plan. The possible measures are evaluated and signed off as a combined package with the client, and a Medium-Term Improvement Plan – mandatory under PAS 2035:2023 – is produced, setting out the wider improvement roadmap beyond this immediate project, before design work is finalised (Clause 8.1). On large-scale schemes, an approved archetype IOE and MTIP can be adapted to properties of the same type, with each still reviewed for suitability and any property-specific adjustments needed.
- Design. A Retrofit Designer uses the assessment and MTIP to design the relevant energy efficiency improvements (Clause 8.2). Simple measures – loft insulation, cavity wall insulation, replacement windows and doors, low energy lighting, solar PV, decentralised mechanical extract ventilation – are typically designed together; more complex interventions, such as internal or external wall insulation, need their own detailed junction detailing and moisture and thermal-bridging risk assessment, reflecting the standard’s “concentrate on the interfaces” principle (Clause 5.6).
- Installation, testing and commissioning. The approved measures are installed by the Retrofit Installer or Main Contractor, then tested and commissioned (Clauses 9–10). Compliance ultimately sits with whichever of these holds the PAS Certification for the work.
- Handover and evaluation. The project is handed over to the client, and building performance is monitored and evaluated afterwards (Clauses 11 and 13) – typically including a post-installation EPC survey, air tightness test and ventilation survey to confirm the completed work matches the design intent, continuing the whole-dwelling approach beyond the point of handover.
What Changed in Risk Assessment Under PAS 2035:2023
This risk-assessment step is a genuine departure from the previous version of the standard. Under PAS 2035:2019, every retrofit project was assigned an aggregate risk grade of A, B or C, determined by a triage-based risk assessment set out in a standalone Annex B (“Risk Assessments”), with a different Path of requirements – Path A, B or C – applying to the assessment and design stages depending on that grade. PAS 2035:2023 removed this altogether: risk is no longer graded upfront, and Annex B now covers Industry Quality Assurance Schemes instead. In its place, the Retrofit Coordinator holds continuous oversight of risk across every stage of the project – the dwelling assessment, the retrofit design, installatio, and post-completion evaluation (Clause 6.1.3) – rather than working from a single classification made at the outset.
This is one of fifteen changes introduced in the 2023 revision – see our blog on PAS 2035:2023 Changes for the full breakdown:
What’s Next?
PAS 2035 exists so that retrofit work is assessed, designed and installed to a standard that actually holds up once residents move back in – not just on paper. Our team of award-winning retrofit assessors are ready to support your next retrofit project
We carry out PAS 2035 retrofit assessments, coordination and design in-house, working to the same standard this article describes.
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