PAS 2035 Explained

PAS 2035 is the standard that sits behind almost every publicly funded home retrofit project in the United Kingdom. If you are bidding on — or simply trying to understand — a heat pump, insulation or whole-house retrofit tender that references "PAS 2035" or a "Retrofit Coordinator", this guide explains what the standard actually requires, why it exists, and what it means for anyone delivering work under it.

What PAS 2035 is

PAS 2035 is a Publicly Available Specification published by the British Standards Institution (BSI). Its full title is "Retrofitting dwellings for improved energy efficiency — Specification and guidance", and it sets out how domestic energy-efficiency retrofit projects in the UK should be planned, designed, installed and evaluated. It was developed after the Each Home Counts review into standards and quality in the retrofit and renewable energy sector identified that earlier schemes — including the Green Deal — had suffered from poorly coordinated projects, inconsistent installation quality and, in some cases, physical damage to buildings from measures that were installed without considering how a home performs as a whole system.

PAS 2035 does not stand alone. It works alongside PAS 2030, which specifies the installation requirements for individual energy-efficiency measures (insulation, heat pumps, glazing, ventilation and so on). Put simply: PAS 2030 governs how an individual measure is installed, and PAS 2035 governs how the whole retrofit project — potentially involving several different measures installed by different trades over several visits — is planned, sequenced, monitored and signed off. A retrofit project delivered under PAS 2035 is expected to treat the dwelling as a single interacting system rather than a checklist of separate jobs.

The standard has been revised more than once since its original 2019 publication, most recently with a 2023 update that strengthened requirements around ventilation, airtightness and moisture risk, and introduced a stronger emphasis on medium-term improvement planning so that a single project step (say, loft insulation this year) is chosen with awareness of what may follow (external wall insulation or a heat pump later), rather than in isolation. Retrofit work funded through UK government schemes is generally expected to follow the current version of PAS 2035 rather than an older edition, and procurement documents will usually state which version applies.

Why PAS 2035 exists: unintended consequences

The core problem PAS 2035 was written to solve is what retrofit practitioners call "unintended consequences". A solid-walled Victorian terrace that has cavity or external wall insulation added without also addressing ventilation can trap moisture that previously escaped through the fabric, leading to condensation, mould growth and, over time, damage to timber and masonry. A house that is heavily draught-proofed without any change to its ventilation strategy can suffer from poor indoor air quality. A heat pump installed without a proper heat-loss calculation and without resizing radiators or pipework can run inefficiently and fail to keep the building warm.

None of these risks are hypothetical — they are the reason PAS 2035 sets out a structured, sequenced process with defined roles and sign-offs, so that decisions about ventilation, moisture risk (assessed against BS 5250, the British Standard for control of condensation in buildings) and the interaction between measures are made deliberately, by someone responsible, rather than left to whichever trade happens to be on site. For a public-sector buyer paying for retrofit work with taxpayer or levy funding, PAS 2035 is the mechanism that gives assurance the money is being spent on work that will actually perform as intended for the life of the building, not just at handover.

The five PAS 2035 roles

PAS 2035 defines five distinct roles that a retrofit project must have in place. A single organisation can hold more than one of these roles on a project (subject to competency and, since the 2023 revision, some restrictions on a Retrofit Coordinator also acting as Retrofit Designer without additional recognised qualifications), but the responsibilities themselves cannot be skipped:

• Retrofit Assessor — carries out the whole-dwelling assessment: surveying the building's fabric, existing services, occupancy and condition, and gathering the data the rest of the project is based on.
• Retrofit Coordinator — the role most closely associated with PAS 2035 in public discussion, and the one procurement documents most often name directly. The Retrofit Coordinator owns the project from initial assessment through to final evaluation: commissioning the assessment, developing (or overseeing) the medium-term improvement plan, ensuring a risk assessment is carried out, coordinating the design and installation stages, and making sure the finished project is properly evaluated and monitored. In practice, the Retrofit Coordinator is the single point of accountability for "did this retrofit follow the standard", which is exactly what a public buyer wants to be able to point to when awarding a contract.
• Retrofit Designer — translates the assessment and improvement plan into a technical design for the specific measures being installed, including how they interact with ventilation and moisture control.
• Retrofit Installer — carries out the physical installation, working to PAS 2030 for each individual measure.
• Retrofit Evaluator — checks, after installation, that the work has been carried out as designed and, where required, monitors in-use performance.

Training and certification for these roles — particularly Retrofit Assessor and Retrofit Coordinator — is provided by a number of accredited training organisations and awarding bodies operating in the UK retrofit sector, and individuals or firms are commonly listed on industry registers once qualified. Procurement documents for publicly funded retrofit work will typically ask bidders to name the individual or subcontractor holding each role, and to evidence their qualification, rather than accepting a generic assurance that "PAS 2035 will be followed".

The PAS 2035 project stages

A PAS 2035 compliant project generally moves through a recognisable sequence, even though the standard describes it in more formal terms:

1. Initial engagement and whole-dwelling assessment — the Retrofit Assessor surveys the property, its occupants' needs, and its existing performance.
2. Risk assessment — moisture, ventilation and other risks are assessed for the specific dwelling, not assumed generically.
3. Medium-term improvement plan — a sequenced plan for the measures the dwelling needs over time, so that a single funded intervention is chosen in the context of where the building is heading, not as a one-off.
4. Design — the Retrofit Designer specifies exactly how the chosen measures will be installed and how they will interact with the rest of the building.
5. Installation — carried out to PAS 2030 by appropriately certified installers.
6. Commissioning and handover — including instructions for occupants on how to operate any new systems (a heat pump, for example, is typically operated differently from a gas boiler).
7. Evaluation and monitoring — checking the work was completed to design, and, for larger or innovative projects, monitoring in-use performance afterwards.

Why this matters if you are bidding on a retrofit tender

Almost every major UK domestic retrofit funding route in current use — whether that is a local authority's Social Housing Decarbonisation Fund allocation, a Warm Homes-branded scheme, or ECO4 obligation work delivered by an energy supplier's contractor network — expects PAS 2035 (or, for single-measure jobs, PAS 2030 alone) to govern how the work is delivered. Public sector buyers publishing tenders for retrofit or heat pump installation work routinely require bidders to demonstrate:

• a named, appropriately certified Retrofit Coordinator responsible for the contract;
• access to certified Retrofit Assessors, Designers, Installers and Evaluators for the measures being tendered;
• a track record of delivering PAS 2035 compliant projects, often evidenced through TrustMark registration, since TrustMark is the government-endorsed quality scheme that retrofit businesses use to show they meet these standards; and
• an understanding of how the specific measures in scope (insulation, heat pumps, ventilation) interact, rather than treating them as independent line items.

For a contractor without in-house PAS 2035 capability, the practical route into this market is usually to partner with, or directly employ, a certified Retrofit Coordinator and Assessor, since these two roles are almost always what a tender evaluation is checking for first. Retrofit Designer, Installer and Evaluator capability can more easily be built around specific trades already held by a construction or building services firm.

PAS 2035 and the frameworks that route funding into contracts

Funding programmes rarely contract directly with individual installers at scale. Instead, social landlords and local authorities frequently use pre-tendered procurement frameworks — set up by consortia that exist specifically to give registered providers and councils a compliant route to appoint contractors without running a full standalone procurement for every project. These frameworks commonly build PAS 2035 competency directly into their supplier qualification criteria, meaning a firm that cannot evidence Retrofit Coordinator and Assessor capability is unlikely to get onto the framework in the first place, regardless of how competitive its pricing is. Getting PAS 2035 capability in place — whether by qualifying staff or by partnering with a certified coordinator — is therefore often the first practical step for a contractor that wants to bid on retrofit work funded through these routes, ahead of any pricing or capacity discussion.

PAS 2035 versus Building Regulations

It is worth being clear about what PAS 2035 is not. It is not a replacement for Building Regulations, and following PAS 2035 does not remove the need to comply with Part L (conservation of fuel and power) or any other applicable Part of the Building Regulations for the work being carried out. PAS 2035 sits alongside statutory building control as a process and quality-assurance standard specific to retrofit, addressing questions Building Regulations do not — such as how a whole-dwelling improvement plan should be sequenced, and who is accountable for the project as a coordinated whole rather than as a set of separate regulated works. A retrofit project delivered under PAS 2035 will typically still need to satisfy Building Regulations for the individual measures installed; the two frameworks are complementary rather than alternatives, and a competent Retrofit Coordinator will be familiar with both.

Common points of confusion

Because PAS 2035, PAS 2030 and TrustMark are often mentioned in the same breath, it is easy to conflate them. A short summary of how they relate:

• PAS 2035 governs the whole retrofit project — assessment, planning, design, coordination and evaluation — at dwelling level.
• PAS 2030 governs the installation of an individual energy-efficiency measure to a defined technical standard, regardless of which wider project it sits within.
• TrustMark is the government-endorsed quality scheme that registers businesses meeting the relevant PAS standards for the work they carry out, and is frequently the mechanism a funding body or framework uses to check a contractor's compliance without re-inspecting every project itself.

A related point of confusion is between the Retrofit Coordinator and a general "project manager" role on a construction contract. The two are not interchangeable: a project manager is typically concerned with programme, cost and general contract administration, while the Retrofit Coordinator's responsibility under PAS 2035 is specifically the technical integrity of the retrofit — ensuring the assessment, risk analysis, design and evaluation stages actually happen, in the right order, before the next stage starts. On larger contracts both roles exist side by side; on smaller ones, a single suitably qualified individual sometimes holds both, provided they hold the recognised retrofit qualification as well as general project management competence.

What buyers actually check for at tender stage

Because PAS 2035 evidence requirements can otherwise become a paperwork exercise, most public sector buyers and procurement frameworks concentrate their evaluation on a small number of concrete checks rather than asking for the standard to be recited back to them. In practice, that usually means asking bidders to name the specific individual (not just "a Retrofit Coordinator will be assigned") who will hold each PAS 2035 role for the contract, to provide evidence of that person's current qualification and any relevant register listing, and to describe how the medium-term improvement plan and risk assessment stages will actually be delivered for the properties in scope — including who signs off the ventilation and moisture strategy before installation starts. Bidders who can answer these questions with named individuals and a described process, rather than a general statement of intent, are consistently easier for an evaluation panel to score with confidence, which is a large part of why PAS 2035 capability is worth establishing before a tender closes rather than during the bid itself.

Where to find PAS 2035 tenders

RetrofitTenders tracks public procurement notices for heat pump and building retrofit work across UK Contracts Finder, TED (the EU's Tenders Electronic Daily) and SAM.gov, classifying each notice for retrofit relevance daily. Many UK notices for retrofit and decarbonisation work name PAS 2035 or the Retrofit Coordinator role directly in the tender description — see the UK tenders list for current opportunities, and the SHDF and retrofit frameworks guide for how social housing decarbonisation funding is actually procured once it reaches contractor level.