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U-VALUES: WHEN LOWER MEANS HIGHER

A U-value or rating is a term you will frequently hear when discussing glazing. The U-Value indicates the level of heat loss and is measured in units of W/m2k. The Lower the U-Value the less heat is lost and higher thermal performance is achieved.

Its also important to note that the U-Value is not specific to glazing it is also calculated for other materials such as insulation and other building materials.

There are also 3 main sub values of the U-Value when it is applied to glazing calculations:

  • Ug Value = How thermally efficient the Glass Panel is
  • Uf Value = How thermally efficient the framework is
  • PSIG = How thermally efficient the Spacer is

You choose from a range of door options to enhance your glass box extension and provide a seamless transition between your exterior and exterior.

Most clients choose our slimline sliding doors which can slide back to open up your extension to your garden or patio area.


As you can see different glass options will give different U-Values. This will allow you to achieve the required U-Value to meet building regulations without compromising on the end result. (The image used is for illustration purposes only). Our team can explain this in more detail at quote stage.

To lower the U-Value of the glass it is common to choose at least double glazed panes to ensure a minimum level of insulation, a variety of coatings can also be applied to increase the thermal efficiency of the glass and often an inert gas such as argon gas is used to fill the void.

All this should help the property to retain more heat with less thermal transfer to the outside, which can actually lead to overheating of the property which can then be combated by the use of venting and air conditioning or my altering other building materials used in the plan.