PAS 2035 retrofit standard explained

PAS 2035 retrofit standard explained

If you are a homeowner applying for a government grant to insulate your walls or loft, you may encounter the term “PAS 2035” and wonder what it means for your project. PAS 2035 is the process standard for whole-house retrofit in England, Wales and Scotland, it is not a product standard but a design-and-install quality framework that became mandatory for most publicly funded work in 2021 (DESNZ / BSI, 2023).

The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Without PAS 2035 compliance, your installer risks having the grant reclaimed by Ofgem.

What PAS 2035 actually requires from the first site visit

The standard demands a “whole-house approach”, the assessor must consider building fabric, ventilation, heating and occupant behaviour together, not treat measures in isolation. A retrofit co-ordinator (qualified to PAS 2035/2030) produces a Medium-Term Improvement Plan based on the RdSAP assessment of your home. Every measure must have a risk level (low, medium, high) assigned using the BSI “PAS 2035 risk matrix”, high-risk measures require a detailed design by a retrofit designer (BSI PAS 2035:2019, clauses 5.2–5.4, 6.1–6.4).

This means your installer cannot simply add insulation without first checking for damp, ventilation and structural risks. The process adds design time but aims to prevent the problems that arose from earlier, uncoordinated retrofit work such as condensation or interstitial moisture.

How PAS 2035 eligibility determines access to government grants

The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Private homeowners using the Boiler Upgrade Scheme (BUS) are not required to follow PAS 2035, BUS only requires MCS certification for heat pump installation. For ECO4 (Energy Company Obligation), all cavity-wall, loft and solid-wall insulation must be installed under PAS 2035 supervision (Ofgem ECO4 Guidance, Section 3.2).

If you are a private homeowner paying for insulation yourself, PAS 2035 is not legally required, but some TrustMark-registered installers will still follow it as best practice. For grant-funded work, however, there is no opt-out.

Quick numbers cost uplift, grant values and certification volumes

Who must certify the installer MCS, TrustMark and the retrofit co-ordinator

All insulation installers under PAS 2035 must be registered with TrustMark and hold a relevant Competent Person Scheme, for example, CIGA for cavity wall insulation or INCA for external wall insulation. The retrofit co-ordinator must be certified through a BSI-approved scheme such as Elmhurst Energy, Stroma, or BRE Academy. You can check an individual co-ordinator via the TrustMark “Find a Retrofit Assessor” tool. Heat pump installers must additionally hold MCS certification, even under PAS 2035 projects (TrustMark “PAS 2035 installer requirements” page, 2026).

This layered certification means three separate credentials may apply to a single project: TrustMark for the installer, a Competent Person Scheme for the specific measure, and MCS if a heat pump is involved. The retrofit co-ordinator is a fourth qualified party who oversees the whole process.

Understanding TrustMark and Competent Person Schemes for home retrofit

The direct answer PAS 2035 retrofit means a whole-house, risk-assessed design process that is mandatory for most government-funded energy-efficiency work

PAS 2035 is not a product standard, it does not tell you which brand of insulation to buy, but a process standard that requires a retrofit co-ordinator, a medium-term plan, and risk management for every measure. It applies to solid-wall, cavity-wall, loft and floor insulation, plus doors and windows, but not to heating system replacements alone. The standard was updated in 2023 to clarify ventilation requirements and the role of the retrofit designer (BSI PAS 2035:2023 amendments document).

For homeowners, the practical effect is that your project will take longer and cost more upfront, but the risk of condensation, damp or thermal bypass is significantly reduced compared to older, uncoordinated installation methods.

How to verify a PAS 2035-compliant project before you sign a contract

Ask the installer for the retrofit co-ordinator’s name and certification number, then check it on the TrustMark “Find a Professional” database. Request the Medium-Term Improvement Plan (MTIP) before work starts, it must show the sequence of measures and the risk level for each. Confirm that the installer holds a TrustMark licence and the relevant Competent Person Scheme for the specific measure, such as CIGA for cavity wall or INCA for EWI (TrustMark “Retrofit” section).

How to check your installer's certifications before signing a contract

If the installer cannot produce the MTIP or the co-ordinator’s certification number, that is a red flag. The MTIP should be a written document, not a verbal promise, and it should reference the RdSAP assessment data for your specific property.

What happens if a property does not meet PAS 2035 requirements after installation

The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. The homeowner retains the work but loses the grant; the installer may be required to redo the work at their own cost (Ofgem ECO4 enforcement guidance, Section 7.2, updated 2026).

In practice, this means you should keep copies of the MTIP, the co-ordinator’s certificate, and the TrustMark registration for at least two years after completion. If Ofgem reclaims the grant, the installer, not you, is liable for the repayment, but the administrative burden of proving compliance will fall on you if the installer becomes unresponsive or goes out of business.