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Energy Efficiency: What is a U-Value?

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Energy Efficiency: What is a U-Value?

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Published on: July 19th, 2011

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Diagram showing cross section of double glazing and the sunIn the ongoing search for carbon neutrality and environmental sustainability; it is now required by law that your window and door manufacturer shows you calculated U-values on your new units. Building regulations also state that the final U-value for any new unit must not exceed 1.6 w/m2K; except is certain (typically historic) housing authorities. So what is a U-value?

What is a U-value

A U-value is the rate of heat loss through a material. The lower the U-Value, the less heat will be lost and the more efficient (and money saving) the unit will be.

Typical U-Values:
This value is always measured from the least efficient point, the centre of the pane.

– Single glazed window – 5.6 w/m2K.

– Double glazed window, with standard air cavity – 2.8 w/m2K.

– Double glazed window, with argon-filled cavity – 2.6 w/m2K.

– Double glazed window, (low E glass) with standard air cavity – 1.8 w/m2K.

– Double glazed window, (low E glass) with argon-filled cavity – 1.5 w/m2K.
<3>Beware of Cheap Alternatives:

The British Woodworking Federation (BWF) have issued this statement:

“We hear that many window manufacturers are still not meeting their obligation to demonstrate the thermal performance of their windows and external door-sets and may not be achieving the necessary levels.”

They continued with this warning to consumers; “This is seen as a competitive advantage as poorer thermal performance can mean lower costs but a customer would be accepting work which did not comply with the Building Regulations and a manufacturer would be supplying a product which was not fit for purpose.”

Why Choose Gowercroft Joinery?

Our quotes accurately detail the U-values of each individual unit. We only use double glazing with low-e glass, argon-filled cavity and warm-edge spacer bars; except where restricted by local authority and housing associations. Our standard unit significantly out-performs the government regulations, with a glazing unit centre-pane value of approximately 1.1w/m2K.

If you have any questions regarding U-values, please post comments below this article, as your thoughts (and our responses) may be of interest to other readers.