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The first double glazed window was invented in America in 1930 by Mr. C. D. Haven, and later patented by the Libbey-Owens-Ford Glass Company of Toledo, Ohio under the trade name Thermopane. However, it is thought that homeowners in Scotland in the 1870s installed an extra layer of glass over an existing pane to create the same effect and protect themselves from the harsh Scottish elements.

Double glazing didn’t become commonplace in the rest of the UK until the 1970s. Since then it has grown in popularity to the point where it is pretty much standard.

Over the last forty years, although the scientific principles remain the same, the technology that manufacturers now employ has advanced dramatically. This has been prompted by changes in Building Regulations that dictate that any new build housing is subject to stringent thermal heat loss regulations to make them more energy efficient.

How does double glazing work?

Double glazed windows work by trapping a layer of air, which is a natural insulator, between two panes of glass. This stops the air from circulating which significantly lessens convection resulting in a decrease of heat loss across the window.

This has a double benefit because not only does it help to reduce the cold getting into a property, it also maintains the heat that is already in a house because heat transfer is greatly reduced across the thermal barrier.

How solar gain works example.

How does double glazing insulation work?

Many factors go into making modern double glazed windows as thermally insulating as possible. These include:

  • The space between the double glazed panes is now filled with argon gas that has a 34% lower thermal conductivity to air.
  • The gaskets that are used to secure the glass in place have a high thermal rating and are extruded into the window’s profile to ensure they hold fast at all times and do not shrink to always ensure an airtight seal.
  • The spacers used to keep the glass apart are made from a non-conductive polymer plastic that eliminates heat transfer.
  • The glass has a metallic coating that reflects heat back into the room while allowing heat and light from the sun, known as passive solar heat gain, to pass through.

Double glazed uPVC window cross section.

The result of these innovations is that double glazed windows manufactured in 2016 are much better at keeping the heat in, and the cold out, than those that were produced 20 or even 10 years ago.

How do modern double glazed windows help to reduce noise?Cream timber sash windows on cottage near Leicester.

As well as being an excellent thermal insulator, double glazing helps to reduce the amount of noise that comes into a property compared to single glazing. This is because sound is produced through vibrations and the energy in a sound wave travels away from its source until it reaches our ears. So, if there is another layer of glass to get in the way of the sound wave less audible noise will enter the room.

The more significant the gap between the panes of glass, the greater the acoustic insulation benefits. This can be improved by making one pane of glass thicker than the other, for example, 6mm on one side and 4mm on the other. This is because the differing thicknesses change the properties of the sound wave making it less intense.

Unfortunately, trickle vents that are used to increase ventilation around a window can have a negative impact on sound screening because they create an opening through which the sound can travel. It is possible to fit special acoustic ventilators that solve this problem.

Triple glazing can prove to be effective but, for the reasons explained above, its maximum benefits are only realised if the panes of glass are different thicknesses.

The best way to reduce noise ingress is by installing what is known as secondary double glazing. Many properties around airports along busy roads employ this method. This involves fitting another pane of glass over the entire primary window thus creating a much larger space between the two surfaces. The larger space, the better the acoustic insulation.

How much money will double glazed windows save me?

According to figures published by The Energy Saving Trust as much as 20% of all heat loss in a home is through its windows and doors. Not only does this have a negative impact on a household’s carbon footprint it also increases its fuel bills. With energy prices forever on the rise, it makes complete financial sense to make build a house as thermally efficient as possible.

A window’s thermal efficiency is independently verified by the British Fenestration Rating Council (BFRC), this organisation was formed in 1998 to develop a window-specific rating system in conjunction with the home improvements industry. They came up with a system that is similar to those used on domestic appliances such as fridges, freezers, washing machines and other household products.

BFRC Energy Ratings

The BFRC label clearly indicates the rating of the designated window, A++ to E, depending on the energy efficiency levels achieved by the manufacturer. A++ is the most energy efficient, E the least efficient.

Typically, the higher rating, the more the window will cost. However, this extra spend at installation will be more than recouped over the lifetime of the window. These figures from the Energy Saving Trust show the savings that can be made on various properties annually.

How much energy you can save with double glazing?

By installing double glazing in an entirely single-glazed house, you could save the following each year:

England, Scotland and Wales

Energy rating energy expenditure saving table based on home size.

These savings are for typical gas-heated homes. Figures are based on fuel prices in March 2016

For a detached house with A rated windows, the saving would be somewhere in the region of between £2,400 & £3,100 on energy bills over 20 years.

The other benefit of having an energy efficient home is that it helps to reduce its carbon footprint. This is because less energy needs to be produced in the first place because it’s not being consumed.

The Glass and Glazing Federation has a useful calculator tool, that shows both the energy and carbon savings that can be made by fitting double glazed windows.

By using the calculator, for a detached house with gas heating and UPVC double glazed windows that have a 4-6mm gap between the panes the savings over 20 years are:

Energy                                                                 £3,807.07

Carbon Dioxide                                                 16.05 Tonnes

Carbon                                                                4.38 Tonnes

What does double glazing do?

The benefits of installing double glazed windows are many. In conclusion, double glazing has a role in improving the following:

  • Lower energy bills
  • Reduced carbon footprint
  • Fewer draughts and cold spots
  • Insulation against noise pollution

Therefore, the most enjoyable benefit is that a property is guaranteed to be warmer, cosier and quieter. Exactly like what they were trying to achieve in Scotland in the 1870s.

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