When you think of double glazing, you may also know it as insulating glass. The basic idea of double glazing is two pieces of glass separated by a gap which is either a vacuum or filled with gas.

Originally this type of window was known as a storm window. They were also called double hung windows because the outer layer was removed in the summer and then replaced in the winter to keep the house warm. For added ventilation the storm window was often hung so that it could be opened to let air through.

Traditional storm windows needed to be stored safely during the summer months and cleaned, then rehung as the days became colder.
These days double glazing means that windows can be installed and left through all types of weather.

What’s the spacer?

It is the gap, or spacer, which makes your house warm and snuggly in the winter and cool in the summer. The gap between the glass can vary from anywhere between 6mm to 20mm.

Typically, a glass pane is 4mm thick, although you can use a thicker glass if you want added insulation or need to keep outside noise to a minimum.

The spacer is also sometimes called the ‘warm edge’ and is often made of fibre or metal which are considered more durable. They are also made from structural foam which is less of a heat reflector. Aluminium reduces condensation on the inside of the glass panes.

You can also vary the two panes of glass. For example, the inner pane may be 6mm and the exterior glass 10mm. You may do this if you want to reduce low frequency noise such as traffic.

The idea of double glazing is that two pieces of glass pane will insulate the house better than one single piece.

Why do I need a spacer?

You need a spacer to reduce the heat loss in your house. The gap is filled with an inert gas which is also non-toxic. Because gas is denser than air it effectively keeps the heat inside, instead of letting it pass through the windows.

What are the benefits of thick glass?

Two panes of glass work better than a single frame because it reduces heat loss, which will in turn lower your heating bill. It will also lower your cooling bill because the temperature in the house stays at a more constant number.

The thicker the glass you choose, the better the insulation will be. Further benefits explained here.

How thick will the gap be?

The gap can come in sizes between 6mm and 20mm. For the best energy efficiency, 12mm is most often used. This has been shown to be best for both thermal and acoustic insulation.

The gap is also dependant on the size of your available space for a new window. You may not be able, to or want to, knock the window opening out larger and may opt for thinner windows.

Because of temperatures where you live, you may choose to have the thicker gap and more insulation. Your double glaze company will suggest the best spacer for the region you live in.

Any double-glazing unit, even a most basic one, will do a better job than not having one and any gap thickness will be better than a single pane.

What about condensation?

Will double glazing stop condensation? This is one of the most popular questions customers ask. You should not have any condensation between the two panes of glass. Neither should you have any fogging on the inner glass panes. Fog will tell you that the seal is damaged, and the double glazing is not working as well as it should.

If you find fog or condensation, be sure to get it sorted right away before the problem gets worse. Most double-glazed windows will come with a 10-year warranty just in case this happens.

So, what to do it there is condensation?

Unfortunately, this is not something you can do yourself. Normally if the double glazing is under warranty the company will do this for you.

If the seals are damaged the solution is often to replace the windows. Double glazed windows will eventually have damage happen over time. Moisture will get in and harm or destroy the seal, particularly in wooden windows.

So how do I work out the total thickness of my double-glazed window?

You will need to consider the thickness of the glass you choose. This depends on the area you lie and how much insulation you need. It also depends on how quiet you want your home to be.
For example: it you opt for 6mm glass, you will need 12mm for two panes (inner and outer).

To this you will need to add the size of the spacer. Again, this depends on how much insulation you need and how much noise reduction you plan.

If you select a 12mm gap or spacer, you will have a total of 24mm. This is written up as 6:12:6 and this is what you can expect to hear when you talk to your double-glazing installer.

To sum up

The insulating efficiency and the acoustic insulation are all greatly dependant on the gap or spacer thickness. The ideal thickness for maximum efficiency is around 16mm for the space.

The lifespan of a typical double-glazed window is between 10 – 25 years although this depends on how much direct sunlight the window receives. The more sun, the shorter lifespan of the unit.

The thickness of the glass panes depends on the temperatures where you live and can vary from 4mm.

The seals on the panes of glass make a difference to heat transference and damaging them will compromise the effectiveness of the window, so if you notice fogging or condensation, it is better to let a professional do the repair work rather than attempt it yourself.

Double glazing will not only reduce your heating bills and make your home more efficient, it will also add value to the property as well as curb appeal should you want to sell it.