Conventions for calculating linear thermal transmittance and temperature factors
BRE is an independent, research-based consultancy, testing and training organisation, operating in the built environment and associated industries.
On 3 June 2016, BRE published Conventions for calculating linear thermal transmittance and temperature factors (BR 497 2nd edition), written by Tim Ward, Graeme Hannah and Chris Sanders.
Well-insulated buildings require sophisticated techniques to model heat loss caused by thermal bridging at wall, roof and floor junctions and around openings. Thermal bridging at these junctions can add significantly to fabric heat loss and cause localised reduction in internal surface temperatures, which can lead to surface condensation and mould problems. A more detailed calculation method for U-values, as defined in BS EN ISO 6946:2007, has been introduced to take account of these repeating thermal bridges.
The BRE guide provides the information needed to carry out these calculations so that different users of the same software package or users of different software packages can obtain consistent and reproducible results. It is intended for use by designers and numerical modellers.
For building regulation purposes two key modelling outputs are identified:
These outputs enable designers to assess junction details and develop novel solutions to improve thermal performance.
The second edition of the guide has been updated to include additional junction types and information about how they should be modelled, as well as worked examples giving the determined values of linear thermal transmittance and temperature factors.
The contents of the guide are:
- Introduction.
- Numerical modelling.
- Thermal bridging at junctions.
- Junction types.
- Point thermal bridges, chi-values.
- Reporting of calculations.
- References.
- Appendix A: Detailed Input and Output from a numerical model.
- Appendix B: Worked examples with calculated values of psi and f.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
- Air tightness in buildings.
- Cavity wall insulation.
- Computational fluid dynamics.
- Computational fluid dynamics in building design: An introduction FB 69.
- Conventions for U-value calculations (2006 edition) BR 443.
- Floor insulation.
- g-value.
- k-value.
- Heat transfer.
- Insulation specification.
- Limiting fabric parameters.
- Roof insulation.
- Solid wall insulation.
- Standard Assessment Procedure SAP.
- Thermal admittance.
- Thermal bridge.
- Thermal mass.
- Thermographic survey.
- U value.
- U-value conventions in practice: Worked examples using BR 443.
Featured articles and news
Top 50 firms awarded 52bn of projects in the last year
New engineering data shows.
Enhancing construction site reporting efficiency
Through digitisation and the digital revolution.
Noise in the built environment
BSRIA guide TG 20/2021.
17,000 people suffer conditions as a result of exposure to excessive noise at work.
Turning down the noise: Auditory health
A pervasive risk with far-reaching consequences.
UK Construction Week, London is here !
Debuting major international pavilions and much more.
Getting the most out of heat pumps and heating
How heat pumps work and how they work best.
Plumbing and heating for successful retrofit and renovation
Low temperature underfloor systems and heat pumps.
Cost-of-living crisis and home improvement plans
Starting on the right footing and top tips for projects.
Delays on construction projects
Types, mitigation and the acceleration of works.
From Chaucer to Fawlty Towers.
Electrotechnical excellence, now open for entries.
Net zero electricity grids BSRIA guide NZG 5/2024
Outlining the changes needed to transition to net zero.
CIOB Global Student Challenge 2024
Universitas Indonesia wins for second year running.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.