PAS2035 structures the retrofit process into four defined stages, each with required outputs, defined roles and compliance documentation. Understanding what happens at each stage — and why — is essential for housing associations, local authorities and anyone managing or commissioning retrofit delivery.
Every PAS2035 project begins with a whole-house assessment carried out by a TrustMark-registered Retrofit Assessor. This is substantially more detailed than an EPC survey — it captures not just the energy performance data that feeds into the RdSAP model, but condition data about ventilation, moisture, structural defects and other factors that affect what measures can safely be installed.
The assessment produces an RdSAP report plus a condition survey report. Both are reviewed by the Retrofit Coordinator before Stage 2 can begin. Where the assessor has identified non-conformities — problems that must be addressed before retrofit measures are installed — the RC must document these and ensure they are resolved or managed in the project plan.
The Stage 1 advice letter must be issued to the resident at this stage. This is a PAS2035 compliance document — it must be issued at the correct time and retained as part of the project record.
The Improvement Option Evaluation is the document at the heart of the RC's work. It models a range of retrofit improvement options for the property — comparing different measure combinations in terms of their impact on SAP score, energy bills, carbon emissions, cost and payback. The IOE gives the client the information needed to make an informed decision about what to commission.
The Medium Term Plan translates the IOE into an agreed phased approach to improving the property over time. It sets out which measures will be installed now, which are planned for future phases, and how the sequencing ensures that earlier measures do not compromise later ones.
Common failure point: IOEs that model only one option rather than a genuine range, or that omit the ventilation implications of proposed fabric measures, are one of the most frequent causes of PAS2035 non-conformities at TrustMark lodgement.
The retrofit design is produced by a qualified Retrofit Designer and must cover the full specification of all measures to be installed, the ventilation strategy, and an overheating assessment where relevant. The RC reviews and signs off the design before installation begins — this sign-off is a formal compliance step, not a formality.
Where the design differs from what was agreed in the MTP — for example because a technical constraint has been identified or a resident has requested a change — the RC must document the reason and update the project record accordingly. Undocumented changes to the agreed scope are a common source of lodgement problems.
PAS2030-certified installers carry out the works under the oversight of the RC. The RC does not need to be on site for every installation, but must have a clear process for monitoring quality, recording non-conformities and ensuring they are resolved before handover.
On completion, the RC produces the claim of compliance — the formal statement that all PAS2035 requirements have been met for the project — and the project handover pack for the resident. The project is then lodged with TrustMark, creating the permanent compliance record.
Post-handover, PAS2035 requires monitoring and evaluation of the installed measures. Basic M&E — a documentation review and comparison of as-installed measures against the design — must be completed between three and six months after handover.
Our accredited team works with housing associations, local authorities and installers across the UK.
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