High-quality assessments are the foundation of a successful domestic retrofit project. Without them, even the most well-intentioned measures may deliver limited results, leaving homes underperforming and residents dissatisfied. That’s why the introduction of BS 40104: Retrofit assessment for domestic dwellings – Code of practice is such a significant milestone for the sector.
Published in August 2025, BS 40104 sets out a clear, standardised framework for whole-house retrofit assessments, aiming to improve quality, consistency, and confidence across the industry.
Why BS 40104 matters
Retrofitting homes is essential if the UK is to meet its 2050 net zero target. Housing remains one of the biggest contributors to emissions, with almost 60% linked to heating homes. While measures such as insulation and low-carbon heating are vital, they deliver real benefits when they’re based on a thorough, accurate assessment of the property.
Up until now, PAS 2035 set out the overall retrofit process but offered limited detail on how assessments should be carried out. This has led to variation in practice, inconsistency in assessor training, and, in some cases, missed opportunities or unintended risks. BS 40104 seeks to address this gap, giving retrofit assessors a stronger foundation to work from.
While not a mandatory requirement under PAS 2035, BS 40104 complements the PAS framework by setting out a more detailed methodology for carrying out assessments. At present, PAS compliance alone does not guarantee alignment with BS 40104, meaning standards can vary depending on client requirements.
This raises an important commercial consideration. Retrofit Assessments are the foundation of every project, and the quality of that assessment directly impacts the accuracy of design, the effectiveness of chosen measures, and ultimately resident outcomes. A thorough Retrofit Assessment of a typical 2–3 bedroom home can take several hours, from evidence gathering on site through to the production of a detailed report. While the “light-touch” approach may appear cost-effective, it risks missing critical issues, leading to higher costs or performance gaps later in the project.
At VOR, our ethos is to go beyond minimum compliance. By applying best practice from BS 40104 and combining it with PAS 2035 standards, we provide assessments that give clients confidence their projects are underpinned by reliable data, comprehensive assessments, and confidence that the measures designed will perform as intended.
What’s in the standard?
BS 40104 outlines a seven-stage process for effective retrofit assessment:
- Desktop research – Reviewing regulatory, planning, and geographical constraints, including flood risk, radon exposure, or heritage restrictions.
- On-site condition assessment – Inspecting internal and external elements, identifying defects, and applying a standardised risk rating.
- Ventilation assessment – Checking airflow, systems, and circulation to avoid damp and mould risks post-retrofit.
- Occupancy assessment – Understanding resident behaviour, fuel use, comfort levels, and future plans to ensure retrofit solutions fit real-life needs.
- Energy performance assessment – Establishing baselines using models like RdSAP or SAP, with options to reflect non-standard occupancy patterns.
- Site-specific and heritage considerations – Factoring in obstacles such as loft boarding, satellite dishes, or listed building requirements.
- Data collection requirements – Standardising drawings, photographs, condition reports, and assessor details to build a robust national dataset.
By following this structure, BS 40104 aims to reduce inconsistencies, highlight risks earlier, and instill confidence in the process.
The bigger picture
Standards such as BS 40104, and PAS 2035, are key to scaling retrofit delivery without compromising quality. They provide the structure needed to de-risk projects, improve outcomes for residents, and ensure measures deliver the intended energy and carbon savings.
At VOR, we see BS 40104 as a welcome step forward. A standardised approach to assessment means retrofit programmes can be more reliable, fundable, and effective.
