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Window insulation and double glazing

If your windows only have single glazing, then it's likely that you'll be losing 10-20% of your home's heat through them. Windows and doors account for a significant portion of heat loss, so any measures you can take to prevent this happening are worth considering and will help you save on your energy bills. Read this guide for essential information about window insulation and double glazing.
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Door with double glazed windows

How much heat is lost through windows?

If your windows only have single glazing, then you could be losing up to 20% of your home's overall heat through them. Windows and doors account for a significant portion of heat loss, so any measures you can take to prevent this happening are worthwhile to help save on your energy bills.

What can I do to prevent heat loss through windows?

One obvious measure is to replace windows and doors, including frames, with double - or triple - glazing. This reduces heat loss through the windows and resolves any issues with draughts as well. This can, however, be very expensive, especially if you opt for uPVC frames. The cost of double glazing can run into several thousand pounds and it will take decades to recover this in savings on your bills. There are other advantages though, such as the fact that there's no need to paint uPVC window frames, which saves on maintenance costs.

How does double glazing work?

Double glazing achieves heat savings, as the name suggests, by having two panes of glass about 16 millimetres apart. This works best if there's a vacuum between the panes, or some manufacturers use a special gas instead, often argon. This is known as a sealed unit. Having a deeper and accessible cavity of up to 100mm or more can sometimes be an option - the larger gap protects against external noise such as aircraft and traffic, and some suppliers offer triple glazing sealed units.

What types of window frame are available?

In the past, window frames were typically metal, but nowadays the choice tends to be between softwood, hardwood and uPVC. uPVC, or plastic, windows generally contain steel for added strength. There are also composite windows, although these are not nearly as popular as composite doors. Composite windows and doors consist of an inner, which is usually wood; this is coated with a protective layer not unlike uPVC to protect it from the weather. It is a low maintenance option as it doesn't need painting, but comes in a grain effect, which gives it the appearance of wood, rather than the simple flat finish of uPVC. It's generally available in a variety of colours.

Does the energy efficiency rating apply to windows?

There's an A to G energy efficiency rating system that applies specifically to windows, look for the BFRC energy efficiency label and ensure you use an authorised retailer. It's worth remembering, however, that some uPVC doors and window frames are no more energy-efficient than wooden ones, and the inefficiency of old windows and doors has as much to do with the glazing and draughts as with the material that the frames and non-glazed panels are made of. If you're set on having completely new window frames, consider triple glazing or low-emissivity (Low-E) double glazing. This is glass with a special coating which enables a better thermal performance than that of normal glass.

Should I change the size of the opening casements in my windows?

As mentioned earlier, replacing your windows can be an expensive business. Double glazing prices and installation fees can quite easily set you back thousands of pounds. Don't make the mistake of trying to cut the cost by reducing the number of opening casements, or by specifying fewer and larger opening casements. This will create security and ventilation issues.

Larger opening casements make it harder to have a suitably low level of ventilation, and if they are accidentally left open, they create more of a security risk. Having said that, it's a good idea to have at least one larger opening casement in each room, as this can be used as a means of escape if there is an emergency.

How do I know my double glazing is working?

From time to time sealed units can fail and will need replacing. You can usually tell when there's a problem as condensation or droplets will appear between the two panes of glass. Most suppliers offer a guarantee - usually 10 years - and will replace windows free of charge if they fail within the guarantee period.

Will I be able to fit double glazing if I live in a conservation area?

If you live in a conservation area or in a listed building it is best to discuss any plans you have with your local conservation or planning officer, as there are restrictions which might vary from area to area. uPVC replacement windows are typically not allowed, though.

You may be able to replace your existing pieces of glass with sealed units, if your frames can accommodate them. Slim units are now available that are suitable for use in many original window frames without the need for replacements. These can have an overall thickness of as little as 12mm with a gas filled cavity and 5mm perimeter seal designed to fit into Georgian style windows to maintain the visually slim glazing bars. A traditional glazer should be able to provide and fit them.

Secondary double glazing is another option, and one which is often overlooked. It's also a potential DIY option, and a strong option for use in conservation areas, as well as locations that suffer from noise pollution, such as under an aircraft flight path or near a main road. The basic concept is to put up a second wall of glazing on the indoor side of the existing pane. Some systems are designed so you can remove them in the summer months, for instance secondary double glazing panes that are held in place with Velcro or magnetic fasteners.

Is double glazing my only option to prevent heat loss?

Double glazing is just one option. There are alternatives and some are cheaper. For many of the options the services of a joiner or handyman might be needed, but to save money, many of them can be carried out as DIY solutions. Read on for some options.

What about temporary 'glazing' in winter?

Putting one of the temporary but purpose-made transparent films - a polymer membrane - on your windows is one way to create a very cheap form of double glazing. Alternatively, products like Ecoease secondary glazing attach to your windows with strong magnetic strips, so you can remove them when the weather gets warmer. Generally, you don't need many tools to do this, although a hairdryer is usually one of them - this creates the heat to make the film shrink until it's taut and smooth. You will also need double-sided tape - which is normally provided with the product - to adhere the film to the indoor side of the window frame.

What about keeping cool in summer?

Insulation isn't just about keeping your home warm when it's cold outside, it's also about keeping it cool when it's hot outside. External shutters are rare in the UK, but popular in France and other southern European countries. These provide added security, and protect against over-heating in summer.

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Solid and cavity wall insulation - Uswitch

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Loft and roof insulation - Uswitch

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Draught-proofing your home - Uswitch

Draught-proofing is a cheap way to prevent heat loss, cut your energy bills and warm up your home. Find out how to draught-proof your home and save money.

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