Conventions for U-value calculations (2006 edition) BR 443
Note: This edition has been superceded by Conventions for U-value calculations (BR443 2e 2019).
BRE (Building Research Establishment) is an independent, research-based consultancy, testing and training organisation, operating in the built environment and associated industries.
Conventions for U-value calculations (2006 edition) BR 443, was written by Brian Anderson and published by BRE on 11 July 2006. The 44 page guide is in line with Part L of the Building Regulations (Conservation of fuel and power) which came into effect in April 2006.
U-values, (sometimes referred to as thermal transmittances and measured in W/m²K) represent how effective elements of a buildings fabric are as insulators. That is, how effective they are at preventing heat from transmitting between the inside and outside of a building. The lower the U-value of an element, the more slowly heat transmits across it, and so the better it performs as an insulator.
Calculation methods for U-values appropriate for demonstrating compliance with the building regulations are based on standards developed by the European Committee for Standardisation (CEN) and the International Organisation for Standardisation (ISO) and published as British Standards. They may be used for the relevant calculations by the Standard Assessment Procedure (SAP) for dwellings or by the Simplified Building Energy Model (SBEM) for other buildings.
Conventions for U-value calculations provides guidance about the calculation of U-values for architects and specifiers:
- It explains the different methods for calculating the U-values of roofs, walls, floors, basements, windows and doors.
- It provides detailed guidance about using those methods.
- It provides data relevant to typical UK constructions.
- It provides guidance about the thermal conductivity of materials.
- It provides guidance about issues that commonly arise when calculating U-values and how these apply to different construction types.
The contents of the guide include:
- Introduction.
- Numerical methods and simplified methods.
- Thermal properties of materials and products.
- Issues concerned with U-value calculations.
- Elements adjacent to an unheated space.
- Expression of results.
- U-values for walls.
- U-values for roofs.
- U-values for floors.
- U-values for basements.
- U-values for windows, roof windows and rooflights.
- U-values for doors.
- Appendix A: Elements adjacent to an unheated space.
- Appendix B: U-values of uninsulated floors.
- References and further reading.
[edit] Related articles on Designing Buildings
- Approved document L.
- BRE articles on Designing Buildings Wiki.
- Building regulations.
- Building Research Establishment.
- Conventions for calculating linear thermal transmittance and temperature factors.
- Conventions for U-value calculations (BR443 2e 2019).
- Energy performance certificate.
- Insulation.
- Kappa value.
- Simplified Building Energy Model.
- Standard Assessment Procedure.
- Thermal bridge.
- Thermal mass.
- U value.
- U-value conventions in practice: Worked examples using BR 443.
- What do design professionals need to know about U-value calculation conventions?
Featured articles and news
Government consultations for the summer of 2025
A year of Labour, past and present consultations on the environment, the built environment, training and tax.
CMA competitiveness probe of major housing developers
100 million affordable housing contributions committed with further consultation published.
Homes England supports Greencore Homes
42 new build affordable sustainable homes in Oxfordshire.
Zero carbon social housing: unlocking brownfield potential
Seven ZEDpod strategies for brownfield housing success.
CIOB report; a blueprint for SDGs and the built environment
Pairing the Sustainable Development Goals with projects.
Types, tests, standards and fires relating to external cladding
Brief descriptions with an extensive list of fires for review.
Latest Build UK Building Safety Regime explainer published
Key elements in one short, now updated document.
UKGBC launch the UK Climate Resilience Roadmap
First guidance of its kind on direct climate impacts for the built environment and how it can adapt.
CLC Health, Safety and Wellbeing Strategy 2025
Launched by the Minister for Industry to look at fatalities on site, improving mental health and other issues.
One of the most impressive Victorian architects. Book review.
Common Assessment Standard now with building safety
New CAS update now includes mandatory building safety questions.
RTPI leader to become new CIOB Chief Executive Officer
Dr Victoria Hills MRTPI, FICE to take over after Caroline Gumble’s departure.
Social and affordable housing, a long term plan for delivery
The “Delivering a Decade of Renewal for Social and Affordable Housing” strategy sets out future path.
A change to adoptive architecture
Effects of global weather warming on architectural detailing, material choice and human interaction.
The proposed publicly owned and backed subsidiary of Homes England, to facilitate new homes.
How big is the problem and what can we do to mitigate the effects?
Overheating guidance and tools for building designers
A number of cool guides to help with the heat.
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.