Understanding U-Values
A U-value (also known as a thermal transmittance value) measures how effective a material is as an insulator. It is expressed in watts per square metre Kelvin (W/m²K). The lower the U-value, the better the insulation.
Why U-Values Matter for Windows
Windows are one of the biggest sources of heat loss in a home. A poorly insulated window can have a U-value of 5.0 W/m²K or higher, while a high-quality double-glazed unit can achieve 1.2 W/m²K and triple glazing can reach 0.6 W/m²K.
What U-Value Should I Aim For?
Building Regulations in England require a minimum whole-window U-value of 1.6 W/m²K for replacement windows. However, we recommend targeting 1.2 W/m²K or better for maximum energy savings.
How to Improve U-Values
The best ways to improve window U-values are: upgrading from single to double or triple glazing, using argon or krypton gas fills between panes, choosing warm-edge spacer bars, and selecting low-emissivity (Low-E) glass coatings.
