28 October 2025 - Comprehensive guidance designed to improve the quality, consistency, and outcomes of retrofit projects across the UK and beyond has been published by BSI, with a goal of helping the UK make use of existing housing supply while also cutting emissions.
Estimates suggest there are nearly 19 million homes across the UK requiring energy efficiency upgrades. However, until now, the retrofit assessment process has lacked clear, consistent guidance. The new standard, Retrofit Assessment for Domestic Dwellings – Code of Practice (BS 40104:2025), addresses this gap by providing a comprehensive, whole-home methodology developed by leading industry experts.
Research by BSI earlier this year found that 76% of Britons want increased refurbishment of existing assets (buildings, homes, infrastructure) in their local area, preferring this over demolition and rebuilding. At the same time, with demand for housing rising, retrofitting properties is a strategic priority for the UK government in order to meet climate targets, reduce energy bills, improve the quality of housing and enhance occupant health and comfort.
BS 40104:2025 is designed to respond to this, by providing clear recommendations and guidance on all critical aspects of retrofit assessment. It covers a range of key areas, including context and condition assessments, ventilation and occupancy evaluations, and energy performance within the site-specific context. The standard also outlines requirements for significance assessment, reporting, and lodgement, ensuring thorough documentation and compliance. Additionally, it sets out the necessary competency requirements for professionals conducting assessments, promoting high standards and consistency across retrofit projects.
This risk-based, whole-house approach ensures retrofit projects are founded on rigorous, site-specific analysis that balances energy efficiency with people’s well-being and, where applicable, heritage conservation. By establishing standardized processes and competency criteria, the aim is to build trust among homeowners, funding bodies, and retrofit suppliers, promoting transparency and accountability in an industry poised for significant growth.
Anthony Burd, Director of Built Environment, BSI, said “With housing demand remaining high and three quarters of us keen to see buildings reused rather than demolished or sitting empty, retrofit is a critical piece of the puzzle – not just in terms of meeting people’s needs for homes, but to achieving net zero, reducing energy costs, and improving health and well-being. Thorough pre-retrofit assessment is key to achieving successful project completion but, until now, standards have not covered the assessment process in significant detail.
“This new guidance has been written by experts across every aspect of the industry. Using a seven-stage process for whole-house retrofit, it provides a comprehensive, risk-based methodology for assessing dwellings before retrofit works are carried out, ensuring projects are based on sound, standardized practice. We hope this can lay the foundation for a thriving retrofit sector that meets both societal and environmental needs.”
Professor Richard Fitton (University of Salford) said: “I was delighted to help develop this standard with an amazing team of experts in the field, all adding unique aspects to the assessment piece. This is a landmark British Standard that formalises how domestic properties are assessed before retrofit works take place.
“This is a major step forward for the retrofit sector,” said Prof Fitton. “For the first time, we have a national standard that clearly defines what a retrofit assessment should include — from understanding the condition and ventilation of a home, to evaluating energy performance, occupancy, and moisture risk. It ensures that every retrofit project starts with a full understanding of the dwelling — not just its construction, but how it’s used and how it performs.
“BS 40104 gives structure and consistency to a part of the process that has often been fragmented,” Prof Fitton added. “It empowers assessors and designers to work from a common framework — one that recognises the complexity of our housing stock and the importance of getting the first stage of retrofit right. In short, it’s about building retrofit on evidence, not assumptions.
“The new standard will support compliance, and the professionalisation of the retrofit assessor role across the UK. It can also underpin research and policy work on housing decarbonisation, helping ensure that energy efficiency improvements deliver genuine benefits.”
The standard aligns with broader government and industry efforts to reduce the carbon impact of the built environment while safeguarding people’s health and comfort. The consistent framework for retrofit assessments aims to support enhanced energy performance and lower household energy bills, improved indoor air quality and ventilation, better protection of building fabric and heritage features, and increased confidence in retrofit investment decisions.
The publication of BS 40104:2025 comes as a recent National Audit Office (NAO) report highlighted many of the same challenges and opportunities addressed by the new standard. The report set out challenges including poor-quality installations, weak oversight and inadequate audit and monitoring.
For further information on the standard, visit https://knowledge.bsigroup.com/products/retrofit-assessment-for-domestic-dwellings-code-of-practice
