Last edited 03 Jan 2021

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Conventions for U-value calculations (BR443 2e 2019)

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BRE (Building Research Establishment) is an independent, research-based consultancy, testing and training organisation, operating in the built environment and associated industries.

The 2019 edition of Conventions for U-value calculations (BR443 2e 2019), was published by BRE in November 2020. It was written by Ludmilla Kosmina, and dedicated to Brian Anderson, the author of the 2002 and 2006 editions, who died unexpectedly in 2016.

Updates to the 2006 edition primarily reflect changes in British, European, and international standards, referring to BS EN ISO standards published from 2017 onwards.

The report is concerned with the calculated U-values of new building elements, including walls, roofs, floors, windows and doors. Guidance is provided for: thermal conductivity of materials; issues that commonly arise when undertaking U-value calculations; and types of construction element, identifying which of the issues apply to which construction type. It does not reproduce the details of the calculation methods, for which the reader is referred to the relevant British Standards and other sources.

For constructions that cannot be handled by the basic calculation methods, the U-value can be calculated by numerical analysis or measured by a hot box method. The report gives guidance on the appropriate standards used for establishing the measured values of thermal transmittance (U-value) and the appropriate standards used for establishing the thermal resistance (R-value) of a construction layer by numerical calculation.

The contents of the 80-page report are:

  1. Introduction.
  2. U-value calculation: Simplified methods and numerical methods.
  3. Details of U-value calculations.
  4. Elements adjacent to an unheated space.
  5. Expression of results and areas to which U-values apply.
  6. U-values for walls.
  7. U-values for roofs.
  8. U-values for floors.
  9. U-values for basements and swimming pools.
  10. U-values for windows, roof windows and rooflights.
  11. Curtain walls.
  12. Dynamic transparent building elements.
  13. U-values for doors.
  14. U-values of existing (old) walls, roofs, and floors in dwellings.
  15. Appendix A: Glossary/definitions.
  16. Appendix B: U-values of uninsulated floors.
  17. Appendix C: Example of calculating U-value for elements.
  18. References and further reading.

The report is available from the BRE Bookshop at:

See also: Conventions for U-value calculations (2006 edition) BR 443.

--BRE Group

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