April 20, 2020
What is a U-value? IQ Spotlight Explains
Written by Rebecca Clayton
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IQ Glass Solutions LTD, Sky House, Raans Road, Amersham, HP6 6FT
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A U value is the given measurement for determining the thermal performance of building materials"
A U value is the given measurement for determining the thermal performance of building materials. It is generally calculated using BS EN 673:1998, the standard test method for determining thermal transmittance in glass and glazing.
The calculated value indicates the heat loss through a material or installation and is measured in units of W/m2K. When the U value decreases it represents a better thermal performance, so the lower the U value the better the thermal performance.
There are various elements of U values that are relevant when thinking about the thermal performance of glazing and glass installations.
Ug value = indicates the thermal performance of the glass panel
Uf value = indicates the thermal performance of framework
Psig = indicates the thermal performance of the glazing spacer
"an overall U value for the installation referred to as the Uw value."
These thermal performances are combined together with the sizes of the opening/framing to give you an overall U value for the installation referred to as the Uw value.
It is the Uw value that is important when attempting to achieve good thermal performance on glass installations, for instance it is the Uw value that matters when looking to achieve levels of Code for Sustainable homes, and later in 2013 building regulations will change to ensure that all new build glazing elements have a maximum Uw value of 1.5 and refurbishments 1.6 W/m2K.
There are various ways of improving the Uw value of an installation. Obviously improving the individual U factors in the calculation will improve the overall thermal performance. Using things like ‘Super Spaces’ will improve the Psi value and using a higher performing glass panel, such as IQ’s Super Insulated Units, will improve the Ug value and overall
"If you hide all surrounding finishes of a structural glass wall it will improve the thermal performance"
thermal performance of a glass system.
For example, the Ug value of a single filmed Super Insulating Unit is generally 0.7 W/m2K, when you replace the standard DGU in IQ’s Minimal Windows sliding doors with a Super Insulated pane it can improve the overall Uw value from 1.5 W/m2K to 1.0 W/m2K.
Also, the way the element is installed and finished will affect the overall thermal performance. If you hide all surrounding finishes of a structural glass wall it will improve the thermal performance and Uw value as the fixings are now insulated by the building surround. Similarly, when the Minimal Windows system is finished flush on all fronts, it improves the thermal performance as the framing is now insulated.
It is also important to note that all standard Uw, Ug or Uf factors given for glass and installations are generally standardisations, the size and finishes do affect the thermal performance of the installation. This can be calculated for you using a standardised Uw calculator.
You can also read our technical page on what is a U value for more information
Contact IQ Glass on (0)1494 722 880