01
Assess
Understand the property, its construction, condition, ventilation and the people living in it.
02
Plan
Decide which improvements are suitable and how they should work together.
03
Install
Install the agreed measures using the correct products, details and workmanship.
04
Check
Commission, inspect and hand the work over with the relevant information and documents.
RETROFIT STANDARDS
PAS 2030 & PAS 2035 without the jargon.
PAS 2035 looks at the retrofit project as a whole. PAS 2030 focuses on how the energy-efficiency measures are installed.
Together they provide a framework intended to reduce the risk of inappropriate measures, poor design and poor installation when homes are upgraded.
2035 plans it. 2030 installs it.
A Publicly Available Specification — usually shortened to PAS — sets out a recognised approach for carrying out a particular process.
For home energy retrofit, the two numbers you are most likely to hear are PAS 2035 and PAS 2030.
PAS 2035
PAS 2035 provides the framework for assessing, planning, designing, coordinating and evaluating the retrofit of an existing home.
It encourages the property to be considered as a whole building, rather than treating every insulation, ventilation or heating measure as an isolated job.
PAS 2030
PAS 2030 deals principally with the installation of energy-efficiency measures in existing homes.
It covers matters such as installation processes, competence, products, equipment, commissioning and workmanship.
The simple version: PAS 2035 helps decide what should happen and how the project should be managed. PAS 2030 helps make sure the agreed measure is installed correctly.
Which version are we using now?
The current retrofit framework is PAS 2035/2030:2023.
The transition from the previous 2019 framework ended during 2025. Older projects may sometimes have transitional arrangements depending on when they were started and the scheme under which they were delivered.
IMPORTANT DISTINCTION
PAS is not the same thing as Building Regulations.
PAS provides a retrofit framework. Building Regulations are statutory requirements. A project may need to satisfy PAS requirements, Building Regulations and the rules of its particular funding scheme.
Why was PAS needed?
Retrofit is not simply about adding as much insulation as possible. A home is a collection of interacting materials, services and people.
If one part of the building changes, something else may change with it.
THE WHOLE-DWELLING APPROACH
A house is a system.
Insulation changes heat flow.
Adding insulation changes heat loss, internal surface temperatures and potentially the way moisture behaves within parts of the building.
Airtightness changes ventilation.
Reducing uncontrolled air leakage can improve energy efficiency, but the home still needs sufficient controlled ventilation.
Insulation changes heating demand.
A property that loses less heat may require less heating input, which matters when heating systems are eventually replaced or redesigned.
The small details matter.
Windows, floors, roofs, reveals, services and changes in construction can create thermal bridges or moisture risks if details are poorly considered.
WHO DOES WHAT?
Meet the retrofit team.
01
Retrofit Assessor
Records information about the construction, condition, energy performance, occupancy and ventilation of the property.
02
Retrofit Coordinator
Oversees the PAS 2035 process and considers the assessment, risks, proposed measures, design and project requirements.
03
Retrofit Designer
Provides technical design and important construction details where specialist design input is required.
04
Retrofit Installer
Turns the design into the finished installation using the specified products, systems and installation details.
What actually happens?
The exact route varies depending on the property, the proposed measures and the funding mechanism, but a properly managed retrofit should have a clear process.
1. Initial contact and eligibility
You may enter a retrofit scheme through an installer, landlord, local authority, energy supplier, referral or funding programme.
Before agreeing to work, make sure you understand which scheme or delivery route is being used and which company is responsible for carrying out the work.
2. Retrofit assessment
A Retrofit Assessor visits the home and gathers information needed for the retrofit project.
This is more detailed than simply looking at an EPC rating. The assessor needs to understand the building and record anything that could affect the suitability of future improvements.
What should the assessment look at?
- Property age and construction.
- Condition of walls, roofs, floors and other building elements.
- Signs of damp, leaks or defects.
- Existing wet-room extract ventilation.
- Existing background ventilation.
- Fuel-burning and combustion appliances.
- Windows and glazed doors.
- Property dimensions and heat-loss areas.
- External walls, gutters, downpipes and drainage.
- Loft spaces and other accessible areas.
- Information about occupancy and energy use.
Expect photographs. A retrofit assessment is intended to create an evidence-based picture of the property, not simply a quick walk around the living room.
3. Coordination and improvement planning
The Retrofit Coordinator reviews the available information and considers how the proposed improvements affect the building as a whole.
A Medium-Term Improvement Plan can also help consider possible future improvements so that today’s work does not unnecessarily restrict what can sensibly be done later.
4. Retrofit design
Where design is required, there should be enough technical detail for the installer to understand what is expected.
This can include dimensions, materials, junctions, ventilation requirements, services, fixings and how the proposed measure interacts with other parts of the building.
Ventilation is part of the retrofit.
Insulation and ventilation should not be treated as completely separate subjects.
Improving the thermal envelope may reduce uncontrolled air leakage. That can make the property warmer and more energy efficient, but moisture from cooking, washing, drying clothes, bathing and simply occupying the home still needs to be managed.
The retrofit process therefore considers the existing ventilation provision and what ventilation strategy is appropriate for the proposed work.
THE AIM
Make the home warmer without creating a moisture problem.
The appropriate ventilation solution depends on the dwelling and the measures being installed. It should form part of the retrofit process rather than being treated as an afterthought.
Read the MyWarmHome ventilation guide →
Pre-Installation Building Inspection.
Before work begins, the installer should confirm that the actual conditions at the property are suitable for the proposed installation.
This is commonly referred to as the Pre-Installation Building Inspection or PIBI.
The inspection should be detailed enough to establish whether the specified measure can be installed safely and effectively at that location.
Particular consideration may be needed where there are moisture problems, building defects, fire-safety issues or services such as gas, electricity, water and telecommunications.
A design saying that insulation should be installed does not mean an installer should simply cover over a defect discovered on the day.
Some measures need closer oversight.
Certain insulation measures involve more complicated junctions, moisture risks, services or installation details. Important parts of the work can also disappear from view as installation progresses.
- EWI — External Wall Insulation.
- IWI — Internal Wall Insulation.
- RIRI — Room-in-Roof Insulation.
- UFI — Underfloor Insulation.
- PHI — Park Home Insulation.
- FRI — Flat Roof Insulation.
Current TrustMark arrangements require additional site oversight for specified higher-risk measures delivered through the PAS framework.
THE INSTALLATION
Where the drawings become reality.
Good assessment and good design can still be undermined by poor workmanship.
Insulation continuity
Gaps and badly treated junctions can reduce performance and create cold areas.
Services
Pipes, cables, vents, meters, drainage and other services need to be properly considered rather than simply worked around.
Hidden details
Important stages should be checked and evidenced before insulation, render, boards or finishes permanently hide the work.
Unexpected problems
If the design cannot be followed, the issue should be raised through the project rather than quietly improvised and covered over.
The handover matters too.
The finished retrofit is not just the insulation, heating system or renewable technology. Information about what has been installed forms part of the project too.
Before the project disappears into history, make sure you understand what documents you should receive.
- Details of the measures installed.
- Relevant workmanship guarantees.
- Relevant guarantee or financial-protection information.
- Electrical certification where applicable.
- Gas or heating certification where applicable.
- Commissioning information.
- Manufacturer and system information.
- Operating instructions.
- Maintenance requirements.
- Contact details for the organisations involved.
MYWARMHOME TIP
Keep your own retrofit file.
Keep emails, specifications, photographs, guarantees, certificates and handover information together. They may become important if there is a problem, you carry out further improvements or eventually sell the property.
Technical monitoring.
Technical monitoring and quality assurance provide another opportunity to identify work that has not met the expected requirements.
Depending on the scheme and project, evidence may be reviewed remotely or an installation may be selected for further audit or inspection.
PAS creates a process to follow, but quality still depends on the people assessing, designing, coordinating and installing the work.
More about technical monitoring →
Questions worth asking.
- Which scheme or delivery route is my project using?
- Who is my Retrofit Coordinator?
- What exactly is being installed?
- Were any defects found during the assessment?
- Are repairs required before installation?
- What is the ventilation strategy?
- What happens to pipes, cables, vents and other services?
- Are there areas that cannot be insulated?
- What guarantees and certificates will I receive?
- Who should I contact if there is a problem after installation?
You do not need to understand every clause of PAS 2035 to ask sensible questions about work being carried out on your own home.
PAS is a process — not a magic shield.
PAS 2035 and PAS 2030 provide an important framework for improving retrofit quality, but standards alone cannot guarantee a good result.
Successful retrofit still relies on a suitable assessment, sensible design, competent installation, effective coordination and meaningful quality control.
For homeowners, the important thing is that there should be a clear reason for the proposed measures and a clear trail from assessment through to installation and handover.
Official information.
Retrofit standards and scheme rules can change. For technical or contractual decisions, check the current requirements that apply to your particular project.