top of page

Pas 2035 – What is it?


Significant improvements need to be made to the energy efficiency of the UK’s building stock if the country is to meet its global carbon commitments.

In 2015 the government commissioned the Each Home Counts review to identify and tackle the high level of failure present in domestic retrofit, and to determine a better process for the retrofit of energy efficient and renewable energy measures. PAS 2035 (PAS 2035: 2019 Specification for the energy retrofit of domestic buildings) was introduced because of this review, with the backing of industry and the government department for Business Energy and Industrial Strategy (BEIS). Following a transitionary period, the government has proposed to make compliance with PAS 2035  becoming mandatory for all public funded projects, which would include ECO funded retrofit projects.

How is Pas 2035 different?

The Pas embraces quality retrofit work, eliminating problems associated with defects, shallow retrofit, accountability, poor design, and performance gap. Pas 2035 delivers a whole building approach to the retrofit process; considering the home, environment, occupancy, and the suitable measures to install. This removes the risk of the retrofit work being considered in isolation, which can unintentionally damage the overall performance of the building.

Lo Res-5975.jpeg

Where is PAS 2035 applied?

PAS 2035 and the Retrofit Standards Framework may be applied to all domestic retrofit activity and embraces work that is initiated, procured, funded, and delivered in a wide variety of ways including:

  • Programmes of retrofit promoted and/or funded by national or local government schemes.

  • Programmes of retrofit initiated and/or funded by landlords, including social housing organisations, private landlords in the domestic sector and commercial property portfolio holders.

  • Retrofit of individual buildings by their owners and/or occupants, including both domestic and commercial owner-occupiers.

  • Retrofit that is integrated with and form part of broader repairs, maintenance, and improvement (RMI) activity related to individual buildings or building stocks.


What is the scope of the retrofit process?

The scope of the process includes:

  • Assessment of dwellings for retrofit.

  • Identification and evaluation of improvement options, as part of the design process.

  • Monitoring and Evaluation of retrofit projects.


The measures and intent include:

  • Improvements to the insulation of the elements of the building fabric and reducing thermal bridging.

  • Improvements to building services.

  • Improvements to the airtightness of the building envelope.

  • Establishing a safe dynamic moisture equilibrium through each element of the building fabric.

  • Improving the resistance of the building envelope to water penetration.

  • Providing metering and monitoring systems to promote the efficient use of energy.

  • Advising building occupants about improvement options appropriate to their homes.

  • Commissioning and handover of all the above.

What is meant by a ‘fabric first’ approach?

Whatever the scale of retrofit, a ‘fabric first’ approach is encouraged as the most cost effective and technically sound. 

The five stages to this fabric first’’ approach are: 

1. Bring the building fabric into good repair, by dealing with defects that inhibit energy efficiency and compromise improvement measures such as water penetration, damp, structural defects, and poor pointing masonry.

2. Implement “low hanging fruit” measures that are low cost and easy to install, e.g., energy efficiency lighting, basic heating controls, better control settings.

Lo Res-5968.jpeg

3. Improve the building fabric by means of insulation and air-tightness measures, and by minimising thermal bridging, to reduce heat losses and demand.

4. Satisfy the remaining heat demand as efficiently as possible using efficient heating technology and responsive controls.

5. Use low zero carbon “renewable” energy technologies to reduce emissions further.

What are the different roles within the retrofit process?

Retrofit Assessors

Retrofit Assessors are trained to undertake a retrofit assessment for dwellings in accordance with PAS 2035. The activities completed within the retrofit assessment include the production of a Reduced Data Standard Assessment Procedure (RdSAP) assessment, a detailed floor plan, a condition report, and an occupancy assessment.

The data collected from these sources is used by the Retrofit Coordinator to formulate a Medium-Term Improvement Plan. Accredited Domestic Energy Assessors (DEAs) are well placed to become qualified Retrofit Assessors due to their extensive knowledge and experience with RdSAP methodology and assessment of existing dwellings.

Retrofit Coordinator

Retrofit Coordinators are required to comply with PAS 2035 for all domestic retrofit projects. The Retrofit Coordinator occupies a vital project management role within the retrofit process and is needed to protect both the interest of clients and the public. They are responsible for overseeing a domestic retrofit project from inception to completion, and will liaise with building owners, and other retrofit project stakeholders, to ensure effective project management. A Retrofit Coordinator can prepare a Medium-Term Improvement Plan, using data from retrofit assessments, to provide a scope for improvement over a 20-30 year period.

Retrofit Installers

Person or organisation undertaking the physical placement of an energy efficiency measure(s) in an existing building.


How does it all work?

Like all British Standards, PAS 2035 is a lengthy and dense document. But if you boil it down, the PAS introduces a simple six-stage process, that all retrofit projects must follow.



Source: Enviro AC

bottom of page