U-values are a measure of how good a material is as an insulator. The lower the U-value, the better insulator. A single glazed window would be approx 5 – whilst a double glazed window would be around 1.6 watts per metre squared Kelvin ( Wm²/K)


Keeping a property warm is a concern to us all. The price of energy is rising and so when you are installing new window or doors, extending your property or building from scratch the U-Value becomes important.

You can find out more about the type of glass we use in our windows here.


Building regulations are driving us towards achieving lower and lower U-Values. A low U-value is important for energy saving – whether it is to reduce the heat into the building on very sunny days or to retain heat in cold winter weather. You can choose to install triple glazing. There are three sheets of glass and two airspace widths to improve the thermal insulation and reduction in noise.

Increasingly people are asking for triple glazed units.  Currently building regulations specify that any new window that is install must have a U-Value that is at least 1.6 Wm²/K . When considering triple glazing, whilst the benefits of the lower U-Values should be of interest it is necessary to consider the time that it will take to recoup the extra cost of the triple glazing in energy saving. The windows are more expensive to manufacture and are often filled with a more expensive krypton gas rather than argon. Weight restrictions may also restrict the size of the windows. Whilst triple glazing may reduce the loss of heat from your house through the windows and make the house feel warmer, it more expensive that double glazing and therefore is a longer term investment.

Drawing your curtains on a cold winters evening may be a more cost effective solution !


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Document L covers the insulation values of building elements.

This approved document gives guidance for compliance with the Building Regulations for building work carried out in England.

You can find out more about Document L  here.