The U Value Of Double-Glazed Sash Windows!

With energy prices at their current level, it is more important than ever to ensure that your home is as thermally efficient as possible. There are a range of different features that you can include in order to improve the thermal efficiency of your home and reduce the costs of your heating bills, not least the evolution of existing windows into the double-glazed sash windows in London and cross the South of England that we are proud to offer.

Whilst you cannot add materials to a window to improve its energy efficiency, one of the most important features of a particular material as a heat insulator is its U value.

What Is A U Value?

Simply, the U value is how effective the material in question is as a heat insulator. The formula for calculating a material’s U value is w/m2k, which translates as the energy, in watts (w), that is lost per square meter of the material (m2), when the external temperature is at least 1 degree lower than the internal temperature (k).

Basically, the lower the U value of a material, the better it is for heat insulation. The standards put in place by the UK government are:

  • Roof – 0.15 w/m2k
  • Wall – 0.3 w/m2k
  • Windows – 1.6 w/m2k

As you can see, the standards for windows are much higher than those for other aspects of a home, and that is simply because they are much harder to effectively insulate.

The main ways that you insulate other construction properties of a home, such as the wall or the roof, is by adding large amounts of an insulating material. Most likely, you will be familiar with insulation that resembles rolls of fibreglass insulation, space-blankets and various woollen substances that can really improve your home’s insulation.

How Can You Insulate Your Windows?

Simply, you can’t! At least, not in the same way as you might with other aspects of your home. Windows can’t just be padded out with insulation; instead, you need to ensure that you are making the most of industry-leading sash windows in London and across the South.

The glass in these windows, in fact, isn’t really the best insulator of heat – that is why single-glazed windows have such high U values. Instead, double-glazing solutions see the most heat being preserved in the space between the two pieces of glass.

Argon Gas And Heat Retention

The ‘dead’ space between the two panes of glass isn’t just filled with regular air, as many people believe. Standard air has a U value of 0.024 w/m2k, but the air used in double-glazing solutions is actually Argon. Argon is a colourless, non-reactive and non-toxic gas with a U valued of 0.016 w/m2k, making it almost twice as thermally efficient as air.

Double-glazed sash windows in London are usually treated with low emissivity coating as well, which is highly reflective with regards to heat, which helps to prevent expensive heating from escaping outside during the winter months, and is also effective at reducing the incredibly hot sunlight during summer.

Improve Your Home’s Heat Retention With Double-Glazed Sash Windows In London

Ensuring that your home maintains a high level of heat insulation is extremely important when it comes to making your monthly bills that much cheaper, your home more comfortable and approaching an energy-efficient and sustainable society. Your windows are, more than likely, going to be the weak point of your home’s insulation, so why settle for anything less than the best?

For more information on the benefits that the high-performing insulation sash windows available across the South of England can provide, please don’t hesitate to get in touch with our professional team today on 0800 634 8636.

Alternatively, you can email any questions or queries that you might have to our team directly at


If you would like further information on how we can help to repair, restore or fit any sash windows or doors, please do not hesitate to get in touch with us today. You can call our expert team on 0800 634 863, or alternatively, you can send us an e-mail at