BRE Report (BR) 443 Conventions for U-value Calculations is a document produced by the Building Research Establishment in the UK. As its title suggests, the report details best practice that should be followed by anybody carrying out U-value calculations for building elements.

Although it is not a European Standard (like others that detail actual calculation methods for thermal transmittance), or even a British Standard, BR 443 carries weight in UK construction. It is a widely used and referenced document, recognised as essential to providing accurate U-value calculations.

What is in BR 443?

One thing that BR 443 is not is an explanation of calculation procedures. The document does not describe how to perform a U-value calculation.

What it does give is dimensional and performance data about common UK construction materials and methods. Using BR 443, people who carry out U-value calculations can represent those materials and construction methods consistently, ensuring the industry generally benefits from accurate calculations.

BR 443 contains a wealth of supporting guidance about applying the data, meaning users of calculation software can make informed decisions about inputs into calculation software. There are also checklists for common building elements covering different factors that need to be taken into account when calculating a U-value for that element.

At the time of writing, BR 443:2019 is the current edition, having replaced the one published in 2006. The 2019 document is approximately double in length compared to its predecessor, providing more useful information for readers and significantly expanding some sections (such as section 11 about windows and glazed elements).

A small amount of previous guidance has been removed but, for the most part, the data provided for use in calculations have remained the same. The biggest difference is in the quantity of supporting information.

Traditionally, BR 443 was free to download, but the 2019 edition has to be paid for. As the 2006 edition is still available online, anyone searching for the document should satisfy themselves as to which version they have accessed.

What do architects and design professionals need to know about BR 443?

Any designers who perform their own U-value calculations should already be familiar with BR 443 and be applying its conventions. For designers who obtain calculations from elsewhere, however, do they need to know what is in the document?

Technically, no. The main thing is to be satisfied that whoever is providing calculations for your projects knows BR 443 and is working to its conventions. There are some reasons why having an understanding of its contents could be beneficial, however.

Awareness of common material data, or factors that impact on the thermal performance of building elements, could help to inform design decisions or material specification choices. By factoring that awareness into projects at an earlier stage, it could make it more likely that design intent is realised later on. By contrast, late design and specification changes to compensate for different thermal properties can lead to compromises being made.

Another reason is that when receiving calculations from a third party, such as a consultant or product manufacturer, it’s possible to read those calculations, understand the data that has been used, and ask any questions about the correct representation of your design. Trust that the third party is working to current conventions is important, but being satisfied that you have communicated your design correctly and that it will help to achieve the goals of the project is equally important.

About Polyfoam XPS

As part of the technical support we offer to the construction industry, Polyfoam XPS provides U-value calculations that follow the conventions of BR 443 as standard.

If you have any questions about this blog post, or require advice about U-value calculations for your project, contact us.

Alternatively, to find extruded polystyrene (XPS) insulation products for your ground floor or inverted roof designs, view our complete range of products.