If you've started researching the EPC C upgrade process, you will have encountered the term PAS 2035. It sounds like regulatory jargon, and it often gets treated as such — something to tick a box on rather than understand. That's a mistake, because PAS 2035 is actually the framework that protects you as a landlord if anything goes wrong, and the one that ensures the money you spend on retrofit delivers lasting results rather than just a temporarily improved EPC.
This article explains what PAS 2035 is, how it works in practice, why it exists, and — critically — why you should insist on it for any retrofit work carried out on your properties.
What Is PAS 2035?
PAS 2035 is the UK's Publicly Available Specification for domestic retrofit. Published by the British Standards Institution (BSI) in 2019 and updated since, it sets out the required process for assessing, designing, specifying, and installing energy efficiency improvements in existing homes. It is the overarching framework within which all government-funded retrofit work must be delivered.
It was developed in direct response to a growing body of evidence that poorly specified or incorrectly installed retrofit measures were causing real harm — damp, mould, structural damage, and in some cases significant financial loss to property owners. The Bonfield Review of 2016 (a government-commissioned assessment of the retrofit industry) found that the market was failing homeowners and landlords through inadequate standards, unqualified installers, and a lack of holistic whole-house thinking.
PAS 2035 exists because retrofit done badly is worse than retrofit not done at all. Incorrect insulation can trap moisture. An oversized heat pump wastes energy. A measure that improves SAP on paper can create habitability problems in practice.
What PAS 2035 Actually Requires
The standard defines a clear process with distinct roles and a mandatory sequence of steps. It is not simply a list of approved installers — it is a project management framework for retrofit works.
The Retrofit Assessment
Before any work is specified or carried out, a qualified Retrofit Assessor must conduct a whole-house assessment. This goes beyond a standard RdSAP energy assessment — it includes an assessment of the property's construction type, moisture risk, ventilation provision, heating system condition, and occupancy patterns. The output is a Retrofit Assessment document that forms the foundation for everything that follows.
The Retrofit Coordinator
PAS 2035 mandates the appointment of a Retrofit Coordinator for any project involving medium or significant works. The Coordinator is responsible for overseeing the whole project: ensuring measures are correctly sequenced, that appropriate ventilation is maintained, that installers are accredited, and that the completed works are properly documented and signed off.
This role is the key protection for landlords. The Coordinator is the professional accountable for the integrity of the project as a whole — not just individual measures in isolation.
Retrofit Assessor
Conducts the whole-house assessment, establishes the property baseline, and identifies improvement opportunities and risks.
Retrofit Coordinator
Oversees the project end-to-end. Responsible for measure sequencing, installer accreditation, ventilation strategy, and sign-off documentation.
Retrofit Designer
For more complex projects, produces the detailed technical specification for each measure — required where significant structural changes are involved.
Accredited Installers
Tradespeople who are TrustMark-registered and carry the relevant competency certification for the measures they install.
Fabric First
A core principle of PAS 2035 is the fabric-first approach: insulation and draught-proofing measures should be installed before heating system upgrades. This ensures that a new heat pump or boiler is not oversized for a property that is about to become significantly better insulated — a common and costly mistake when retrofit is approached measure-by-measure rather than holistically.
Ventilation Strategy
One of the most important — and most frequently overlooked — requirements of PAS 2035 is that any improvements to a building's airtightness must be accompanied by a ventilation strategy. Adding insulation to a leaky Victorian house reduces ventilation as well as heat loss. Without addressing this, the result can be condensation, damp, and mould — which creates a habitability problem and potential legal liability for the landlord.
Documentation and Sign-Off
PAS 2035 requires a documented audit trail throughout the project — assessment documents, specifications, installer certifications, and a completion certificate signed off by the Retrofit Coordinator. This documentation is the landlord's legal protection: evidence that works were correctly specified and installed to the required standard.
Why It Matters for Landlords Specifically
PAS 2035 compliance is not currently a universal legal requirement for all retrofit works. However, there are several contexts in which it is mandatory or strongly advisable:
- ECO4 and GBIS funded works. All works funded through government obligations schemes must be delivered under PAS 2035. If you are using grant funding, compliance is non-negotiable.
- TrustMark registration. TrustMark is the government-endorsed quality scheme for retrofit, and from 2023 all TrustMark-registered installers work within the PAS 2035 framework. Choosing TrustMark-registered contractors is the simplest way to ensure compliance.
- Landlord liability. If retrofit works cause harm — damp, structural damage, habitability issues — the landlord's position is significantly stronger if works were carried out under PAS 2035 than if they were not. The Coordinator's sign-off shifts professional accountability appropriately.
- Future EPC assessments. A PAS 2035 compliant project generates the documentation required to evidence improvement works at future EPC assessments, ensuring the SAP uplift from completed measures is correctly captured.
A note on unaccredited contractors
The retrofit market includes many tradespeople who will offer to install insulation, heat pumps, or other measures without PAS 2035 compliance. The work may be cheaper and faster. But if measures are incorrectly specified — wrong insulation thickness, no ventilation strategy, incompatible measure combinations — the remediation cost almost always exceeds the initial saving. For landlords, the liability risk from poorly installed measures in occupied properties is an additional consideration that tilts the calculation firmly towards accredited routes.
What to Ask Your Retrofit Provider
When engaging a retrofit service provider, the following questions establish whether they are operating within the PAS 2035 framework:
- Is your Retrofit Assessor registered with an accredited scheme (Elmhurst, Stroma, ECMK, or Quidos)?
- Will a Retrofit Coordinator be appointed for my project?
- Are all installers TrustMark-registered with the relevant competency certification?
- Will I receive a completion certificate and full documentation at the end of the project?
- How will ventilation be assessed and addressed as part of the works?
A provider who cannot answer these questions confidently is not delivering PAS 2035-compliant retrofit — regardless of what their marketing materials say.
The Bottom Line
PAS 2035 is not bureaucratic overhead. It is the framework that ensures retrofit works deliver the intended outcome — a more energy-efficient, healthier property — without creating new problems in the process. For landlords, it provides the professional accountability structure and audit trail that protects your investment and your legal position.
At Retrofield, every project we deliver is PAS 2035 compliant as standard. Our assessors are scheme-registered, our coordinators are qualified, and our installers are TrustMark-accredited. The documentation you receive at project completion is a complete record of every decision made, every measure installed, and every qualification held.
If you'd like to understand how PAS 2035 applies to your specific property and what compliance looks like in practice, a free consultation is the best place to start.