Technical Glazing Terms

What is the difference between U Values and a BFRC certificate?

There are several factors to consider when it comes to creating an energy-efficient and sustainable building. One of the most important factors of a build is the thermal performance. Once a build is complete, evidence of the thermal performance the build will be required for sign-off. When it comes to the thermal performance of the glazing, there are a number of ways that evidence of thermal insulation can be provided. ed.  

Two of the most common forms of thermal performance evidence for glazing is by a U value calculation or a BFRC certificate.While these terms may seem similar, they refer to different aspects of a building's energy efficiency. But what is the difference between a U values and a BFRC certificate?  

 BFRC certificates 

BFRC certificates are issued by the British Fenestration Rating Council (BFRC) and are used as a means to certify the energy efficiency of windows, doors, and skylights. BFRC certification is based on a combination of factors, including the U-value, solar heat gain coefficient (SHGC), air leakage, and visible transmittance (VT) of the product. 

The BFRC rating system assigns a letter grade from A++ to E, with A++ being the most energy-efficient and E being the least. The rating takes into account not only the U-value but also the other factors mentioned above, which can greatly impact the energy efficiency of a product. 

The certificate is an easy to view and simplified method of understanding the individual component performance of a window. 


 A U-value refers to the thermal conductivity of a material, such as a window or a wall. It is the rate at which heat flows through a material and is measured in watts per square meter per degree Kelvin (W/m²K). A low U-value indicates that the material is a good insulator, meaning it is effective at reducing the transfer of heat between the inside and outside of a building. 

 For example, if a window has a U-value of 1.0 W/m²K, it means that for every degree Kelvin difference between the inside and outside of the building, one watt of heat will be lost or gained per square meter of window. A lower U-value means that less heat will be lost through the window, making it more energy-efficient. 

When it comes to glazing, the U value of a window refers to a combination of the Ug Uf and Psi values which create the overall Uw value for the glazing.  

While this method of evidence for thermal performance is more technical than a BFRC, it provides a more accurate indication of thermal insulation which can then be integrated into the building’s wider thermal performance calcs.  

What is the difference between a U value and a BFRC Certificate?  

While U-values and BFRC certificates both relate to the energy efficiency of a building product, they are different in several ways.  

U-values are a measure of the thermal conductivity of a material and are used to determine how much heat is lost or gained through a product, using quantifiable data driven statistics.  

BFRC certificates, on the other hand, are a rating system that takes into account multiple factors, including U-values and air leakage, however is a considerably less accurate measure of thermal conductivity due to the amount of qualitative data in question.  

U values are more suitable for larger architectural led building projects. Specifiers can use the U values within their full building calculations and have more flexibility to tweak and engineer the thermal performance values to achieve the goals of the building.  

BFRC certificates are more suitable for direct-to-consumer projects or replacement glazing where individual performance certificates are required for the windows rather than an overall building performance, 

  1. Their direct measurement of thermal conductivity provides accurate and reliable information, allowing for precise comparisons between materials. Although BFRC certification considers multiple factors, its reliance on subjective assessments and qualitative data makes it less dependable. When striving for true energy efficiency and sustainability, placing greater emphasis on U-values ensures an optimal outcome for energy-efficient building projects. 


If your project requires high performance glazing solutions get in contact with the team at IQ Glass.