BS 40104:2025

What is BS 40104:2025 - Retrofit assessment for domestic dwellings about? 

BS 40104 Retrofit assessment for domestic dwellings – Code of practice is a new British Standard that provides a comprehensive framework for assessing homes prior to retrofit work. It addresses the lack of standardized pre-retrofit evaluation by offering a whole-dwelling assessment approach. This methodology ensures that retrofit designs are appropriate for the specific characteristics, context, and usage of each home.

This standard was developed in response to the urgent need for the UK to improve the energy efficiency of approximately 19 million homes and it marks a key evolution in the UK’s retrofit framework. Following the success of PAS 2035 and PAS 2030, the national committee CB/401 identified a critical need to go further by establishing clear and authoritative guidance for retrofit assessment. 

Retrofit assessments guided by BS 40104 aim to support better decision-making that enhances energy efficiency, occupant health, and long-term building performance.

It covers key areas such as:

• Context assessment.
  
• Condition assessment.
  
• Ventilation assessment.
  
• Occupancy assessment.
  
• Energy performance assessment.
  
• Site-specific considerations.

Who is BS 40104:2025 - Retrofit assessment for domestic dwellings for? 

BS 40104 is intended for all professionals involved in domestic retrofitting, including:

• Retrofit assessors.
  
• Building surveyors.
  
• Architects and designers.
  
• Retrofit coordinators.
  
• Local authority officers and planners.
  
• Installers (ventilation, insulation, windows, doors, roofs).
  
• Certification bodies and consultancies.

It is relevant across sectors that support energy-efficient retrofit delivery, such as manufacturing, installation, consultancy, and compliance certification, making it a key resource for practitioners working toward national retrofit targets.

What does BS 40104:2025 - Retrofit assessment for domestic dwellings cover? 

BS 40104 provides a structured and detailed methodology for pre-retrofit assessment of domestic dwellings. It includes:

• Assessing the physical and contextual condition of the building.
  
• Evaluating ventilation and occupancy patterns.
  
• Understanding the energy performance of the home.
  
• Conducting site-specific assessments.
  
• Ensuring assessors meet defined competency standards.
  
• Reporting and lodgement procedures.

Although it does not cover fire, gas, electrical safety, or structural evaluations, the assessor is expected to identify and report any visible risks in these areas during their assessment.

Why should you use BS 40104:2025 - Retrofit assessment for domestic dwellings?

BS 40104 is an essential tool for improving the quality and outcomes of retrofit projects. You should use this standard because:

• It provides a formal benchmark for assessing retrofit readiness, improving consistency and reliability across projects.
  
• It reduces the risk of poorly designed or ineffective retrofit work by ensuring decisions are based on evidence and context.
  
• It supports alignment with the Each Home Counts review and builds on the foundation set by PAS 2035 and PAS 2030.
  
• It enhances customer confidence, procurement transparency, and installer accountability.
  
• It is a vital component of the UK’s broader strategy to address fuel poverty, cut carbon emissions, and promote healthier living conditions.

In essence, BS 40104 ensures the first step of any retrofit project is the right one, based on sound data, comprehensive analysis, and best practice.