A complete 2026 guide to PAS 2035, the British Standards Institution specification that governs every grant funded retrofit in the UK. Covers what changed in the 2023 update, the four mandatory roles, links to the Warm Homes Plan and Local Grant, and how the Home Energy Model in 2027 plays into it.
If you have looked into the Warm Homes Plan, the Warm Homes Local Grant, or any government funded energy efficiency scheme in the last twelve months, you will have come across one phrase again and again. PAS 2035. It is rarely explained well, even though it is the single most important standard in the UK retrofit industry and the gatekeeper to nearly every grant pound spent on insulating, ventilating, and heating British homes.
This guide explains what PAS 2035 actually is in 2026, what changed when the 2023 edition replaced the older 2019 standard, who the four mandatory retrofit professionals are, why your local authority will refuse a free upgrade application without it, and how it ties together with PAS 2030, MCS, TrustMark, and the new Home Energy Model arriving in 2027. By the end you will know exactly what your installer, retrofit coordinator, and grant funder are obliged to do before, during, and after any work on your home.
What PAS 2035 actually is
PAS 2035 is a Publicly Available Specification published by the British Standards Institution. The full title is "Retrofitting dwellings for improved energy efficiency. Specification and guidance." It sets out best practice for whole house retrofit projects in domestic buildings from initial assessment through design, installation, testing, handover, and post completion monitoring.
The current version is PAS 2035:2023, published by BSI in September 2023. It officially replaced PAS 2035:2019 at midnight on 30 March 2025, which means every retrofit project funded through a UK government scheme has been delivered under the 2023 specification for over a year now.
PAS 2035 is not a law. It is a specification. The reason it has the force of law in practice is that the government has written it into the funding rules of every major energy efficiency scheme. If a measure is not delivered under PAS 2035, it cannot be paid for from public money and it cannot be lodged in the TrustMark Data Warehouse. No lodgement means no consumer protection, no grant, and no guarantee.
What changed in the 2023 update
The 2023 edition of PAS 2035 brought five material changes that homeowners and landlords should understand before commissioning any work.
First, the old risk paths A, B, and C were removed. The 2019 edition sorted projects into three pathways depending on how complex or sensitive the dwelling was. Path A covered simple low risk projects, Path B covered the bulk of mainstream housing, and Path C covered high rise blocks, listed buildings, and buildings of traditional construction. In 2023 these three paths were collapsed into a single unified process closer to the old Path B, with additional requirements layered on top for higher risk properties such as pre 1919 buildings, system built homes, conservation area properties, and protected buildings.
Second, the Medium Term Improvement Plan became mandatory for every project. Under the 2019 standard it was treated as guidance. Under 2023 it is a hard requirement. The plan is owned by the Retrofit Coordinator and sets out the right order in which measures should be installed over a multi year period, even when the current project only delivers one or two measures. This stops well meaning but counterproductive sequencing. For example, fitting external wall insulation before sorting damp at the wall base, or installing a heat pump before the fabric is improved enough for the heat pump to operate at a sensible flow temperature.
Third, an airtightness strategy is now compulsory whenever a project includes any building fabric measures. The strategy must describe how air leakage is going to be controlled before, during, and after the work. Setting an actual airtightness target and air pressure testing to confirm it has been hit is encouraged but not compulsory. What is compulsory is a written strategy and evidence that the design respects it.
Fourth, the Retrofit Coordinator must now carry out site inspections during construction, either in person or by verified remote means, to confirm that what has been designed is what has actually been installed. Under the 2019 standard this was lighter touch. Under 2023 the coordinator is expected to log inspection evidence as part of the project record.
Fifth, ventilation requirements have been tightened. Any fabric upgrade that reduces air permeability must be paired with a ventilation review under Approved Document F to make sure the home does not become starved of fresh air, which is the single most common failure mode in poorly designed retrofits.
The four mandatory PAS 2035 roles
A compliant whole house retrofit project requires four distinct professional roles. Each is regulated, accredited, and recorded against the project file in the TrustMark Data Warehouse.
The Retrofit Assessor surveys the dwelling in detail. They produce an RdSAP energy assessment, a full set of floor plans, a condition report on the fabric, services and fixed appliances, and an occupancy assessment that records who lives in the property and how they use it. The assessor is the eyes on the ground and produces the information all other roles depend on.
The Retrofit Coordinator is the central role and the one mandated for every PAS 2035 project. They take the assessor's information, evaluate the risks specific to the property, write or sign off on the Medium Term Improvement Plan, oversee the procurement of designers and installers, sign off the design, conduct construction stage inspections, manage handover, and lodge the completed project into the TrustMark Data Warehouse. The Retrofit Coordinator must hold the Level 5 Diploma in Retrofit Coordination and Risk Management and be accredited through a TrustMark approved scheme provider such as Elmhurst Energy, which absorbed Stroma Certification in recent years.
The Retrofit Designer specifies how each measure will be installed in technical detail. For complex measures such as external wall insulation, internal wall insulation on solid walls, or whole house mechanical ventilation, the designer produces drawings, junction details, and specifications that the installer follows. For higher risk properties such as pre 1919 buildings, the designer must hold additional traditional construction qualifications such as the Level 3 Award in Energy Efficiency Measures in Traditional Buildings, or membership of a recognised conservation scheme through CIAT, RIBA, RICS, or equivalent.
The Retrofit Evaluator is the post completion check. On a sample of projects, the evaluator returns to the property to monitor whether the predicted savings, comfort improvements, and indoor air quality have actually been delivered. The findings feed back into industry learning and help local authorities target future grants better.
PAS 2030 and the installer side
PAS 2035 is paired with PAS 2030. They are sister specifications and the two are inseparable in practice. PAS 2035 governs the project. PAS 2030 governs the installation work itself.
PAS 2030:2023 is the installer specification. Any contractor physically fitting insulation, glazing, ventilation, or heating measures under a publicly funded scheme must be certified to PAS 2030 by a UKAS accredited certification body. PAS 2030:2023 came into force on the same date as PAS 2035:2023, on 30 March 2025, and brought stronger digital traceability rules. Every measure installed must be recorded in real time in the TrustMark Data Warehouse with photographs, batch numbers, and operative identification.
For low carbon technologies such as heat pumps and solar PV, the installer also needs MCS certification on top of PAS 2030. The two systems work in parallel. PAS 2030 covers the building fabric, PAS 2035 covers the project as a whole, and MCS covers the renewable technology.
TrustMark and the Data Warehouse
TrustMark is the only government endorsed quality scheme for tradespeople in the UK. It does not certify installers itself. Instead it licenses scheme providers (Elmhurst Energy, NICEIC, NAPIT, HIES, and others) who then approve PAS 2030 contractors and PAS 2035 retrofit professionals.
The TrustMark Data Warehouse is the central record of every funded retrofit project in the country. The Retrofit Coordinator is responsible for lodging the project at completion. Lodgement triggers three things that the homeowner cares about. It releases grant funding to the installer. It generates a Certificate of Lodgement which the homeowner keeps as evidence of the work. And it activates the financial protection guarantee that covers the workmanship and product warranties.
Every TrustMark registered business is required to provide a minimum of two years of financial protection on completed works. For measures funded under the Energy Company Obligation programme and certain other schemes, that protection extends to twenty five years through the TrustMark approved guarantee framework, even if the original installer ceases trading.
Which schemes require PAS 2035 and which do not
This is the question that catches out most homeowners. Not every government grant is a PAS 2035 scheme.
The Warm Homes Plan, which formally launches in January 2027, will require PAS 2035 compliance for every measure. The Plan is the £13.2 billion successor programme that Labour confirmed in November 2024 and aims to upgrade up to five million homes and lift up to one million households out of fuel poverty by 2030. Total public investment under the wider strategy reaches £15 billion.
The Warm Homes Local Grant, which is already running in 2026 and was last updated by the government on 12 March 2026, requires PAS 2035 compliance for every measure. The Local Grant offers up to £30,000 per property towards insulation, ventilation, low carbon heating, and energy efficiency works. It is targeted at homes with EPC ratings of D, E, F, or G and households earning £36,000 a year or less, with an automatic income pass for households living in the bottom two deciles of the Index of Multiple Deprivation. Delivery happens through local councils rather than direct contractors, and the council must use a PAS 2035 retrofit team to scope the project.
The Boiler Upgrade Scheme, by contrast, does not require PAS 2035. The £7,500 grant for an air source or ground source heat pump and the £5,000 grant for a biomass boiler are routed through MCS only. The April 2026 amendments to the Boiler Upgrade Scheme also added air to air heat pumps at £2,500 and removed the previous EPC requirement, but the scheme remains a measure level grant rather than a whole house retrofit programme. There is no Retrofit Coordinator, no Medium Term Improvement Plan, and no TrustMark Data Warehouse lodgement on a Boiler Upgrade Scheme installation.
In practice this means a household can be a Boiler Upgrade Scheme customer without ever coming into contact with PAS 2035. As soon as they apply for any insulation or fabric grant funded by the Warm Homes Plan or the Warm Homes Local Grant, the full PAS 2035 process kicks in.
What it costs and who pays
For grant funded projects the homeowner usually does not pay for the PAS 2035 services directly. The cost of the assessment, coordination, and design is built into the project funding by the local authority or scheme delivery body.
For privately funded retrofits, where a homeowner is paying out of pocket and wants the assurance and guarantee that comes with a fully PAS 2035 compliant project, fees do apply. According to Checkatrade's 2026 cost guide, retrofit coordinator services typically run from £800 to £3,300 plus VAT for a residential project, depending on the scope and risk profile of the property. The retrofit assessor's separate survey work is usually charged on top, often in the £400 to £900 range. For most owner occupier retrofits that figure is small compared with the cost of the measures themselves and the long term value of having a credible whole house plan rather than a bag of disconnected interventions.
What it does for the homeowner
This part is where most explainers fall short. PAS 2035 looks bureaucratic on paper, but its practical purpose is to protect the homeowner from three failure modes that are very common in the UK retrofit market.
The first is unintended consequences. Insulating a wall without addressing damp, putting in a heat pump without sizing radiators correctly, or sealing a house up without upgrading ventilation can all cause more problems than they solve. PAS 2035 makes one accountable professional, the Retrofit Coordinator, sign off the whole sequence of work and consider those interactions in advance.
The second is poor sequencing across years. Most homeowners cannot afford to do everything in one go. The Medium Term Improvement Plan is the schedule of works that gets the property to a low carbon, low bill destination over five to fifteen years, ordered so that earlier measures do not have to be ripped out to deliver later ones.
The third is consumer redress. The TrustMark lodgement, the Certificate of Lodgement, and the mandatory financial protection mean that if the installer disappears, the workmanship goes wrong, or a product fails inside the warranty period, the homeowner has somewhere to turn. The protection is independent of the original contractor's continued trading.
How PAS 2035 connects to the Home Energy Model
The Home Energy Model is the new national methodology that will replace the current Standard Assessment Procedure, RdSAP, and SAP for EPC calculation. On 9 March 2026 the government confirmed that the rollout has been moved to the second half of 2027 to give assessors, software providers, landlords, and the wider industry time to prepare.
When the Home Energy Model arrives, EPCs will move from a single SAP score to four headline metrics: Fabric Performance, Heating System, Smart Readiness, and Energy Cost. PAS 2035 retrofit projects already collect more data than a current EPC requires, including occupancy assessment, condition reporting, and ventilation review, so the standard is well placed to support the new methodology when it goes live.
For landlords aiming at the proposed Minimum Energy Efficiency Standard tightening, currently set for 2030 across the private rented sector, getting work underway in 2026 under PAS 2035 is the safest route. The work is delivered to the highest evidenced standard, the project record is lodged centrally, and the property is positioned strongly for whatever scoring band the new EPC system produces.
How to find a PAS 2035 coordinator
The simplest route is to start with TrustMark. The TrustMark website has a public search function for registered businesses and PAS 2035 retrofit professionals. Filtering by postcode and by service (retrofit coordination, assessment, design) returns a list of accredited people and firms in your area.
The other route is through one of the scheme providers directly. Elmhurst Energy maintains a public register of accredited Retrofit Coordinators, Retrofit Assessors, and Retrofit Designers across the UK. NICEIC, NAPIT, HIES, and other providers maintain similar registers.
If you are applying for the Warm Homes Local Grant, the local council will allocate a coordinator from its appointed delivery partner. The same applies to the Warm Homes Plan when it launches in January 2027. You will not need to source one yourself.
For a privately funded retrofit, especially on a period property or anything more complex than basic top up loft and cavity wall work, it is worth taking the trouble to commission your own coordinator early in the planning. The cost is modest compared with the value of a properly sequenced whole house plan.
Common misconceptions about PAS 2035
That it is the same as PAS 2030. They are different specifications. PAS 2035 governs the project as a whole. PAS 2030 governs the installer's physical work. Both are needed on a funded project.
That a PAS 2030 installer alone is enough. It is not. A funded retrofit needs both PAS 2030 installation and PAS 2035 coordination. An installer cannot self certify the project as compliant.
That PAS 2035 covers heat pump installs under the Boiler Upgrade Scheme. It does not. The Boiler Upgrade Scheme is an MCS only scheme.
That every retrofit must be PAS 2035. Only retrofits funded through PAS 2035 schemes must be. Privately funded works can be carried out outside the standard, although the homeowner loses the financial protection and central lodgement.
That the Retrofit Coordinator is just paperwork. They are an accountable, qualified, regulated professional with legal responsibility for the project record. The role is closer to a project manager and lead designer combined than to an administrator.
The bottom line for homeowners and landlords in 2026
PAS 2035 is the standard that turns a stack of disconnected energy improvements into a coherent whole house plan, with one accountable professional, one project record, and one financial protection guarantee. It is mandatory for every measure funded by the Warm Homes Plan and the Warm Homes Local Grant. It is not required for the Boiler Upgrade Scheme, which uses MCS instead.
For homes earning £36,000 or less, or living in IMD deciles 1 or 2, with an EPC of D, E, F, or G, the Local Grant route in 2026 is the best path to a free or heavily subsidised whole house upgrade, and the work will be delivered under PAS 2035. For everyone else, the Warm Homes Plan from January 2027 will cover a much wider eligibility group, again under PAS 2035.
If you are commissioning private retrofit work, requesting PAS 2035 compliance is the strongest single thing you can do to protect yourself, lock in the long term value of the property, and align the project with the Home Energy Model that will power EPC ratings from the second half of 2027.
If you would like Cucumber Eco to scope your property against the Warm Homes Local Grant or against a privately funded PAS 2035 retrofit plan, get in touch and we will arrange a no obligation assessment.
