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U-values for windows explained

When it comes to windows, you’ve probably heard the term U-values mentioned a lot. Our easy guide helps you get to grips with what it means.

U values

U-values is just a measure of the effectiveness of a material as an insulator. The lower the U-value number, the better the window is at keeping heat inside a building.

The value is measured in watts per square metre per degree Kelvin (W/m²K). For example, if we took a 12 mm double glazed window with a U-value of 2.8, for every temperature degree difference between the inside and outside of the window, 2.8 watts will be transmitted every square meter. Basically, the larger the U-value the more energy that is transmitted/lost from the inside to the outside.

U-values are becoming more and more important for architects, builders and homeowners, as the need for energy efficient and sustainable housing increases. It’s something we pay close attention to throughout the making of our sash and casement windows and the choice of our materials.

U-values for windows

When making a window, it’s necessary to distinguish between U-values for materials. That being:

  • Uw (the overall U value of the window)
  • Ug (the U-value of the glazing)
  • Uf  (the U-value of the frame)

Uw relates to the entire window, and incorporates the U-values for the glazing and the frame. It’s influenced by several factors, including the size of the window. Larger windows normally feature better values and that’s because U-values achieved in glazing are better than in the frame material. Therefore a larger glass area is able to produce a better thermal insulation value.

If you’d like more information about U values, please feel free to give a member of our team a call.

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