Which Windows Provide The Best Insulation?

a window

Reducing energy loss through the most vulnerable area of a building

It’s well known that windows usually cause the most heat loss compared to other parts of a building or structure. In a conservatory most of the surface area is glass, so heat loss is a major factor if looking to use it all year round. Solar gain – the ability of the window to transmit solar energy through itself and thus warm the interior – is another key consideration.

Window technology

There was a time when a humble single pane of glass was used for glazing a window causing much heat loss. To put it in perspective, the U-value (the energy efficiency) of a well-insulated wall is 0.3, whereas a basic single glazed window is around 5.

Double glazing was the next step in improving a window’s energy efficiency, and the earlier types reduced the U-value to around 3; an improvement but still nowhere near as energy efficient as a wall. Things improved with newer double glazing designs with larger gaps between each pane that reduced the U-value to about 1.6 – the level stipulated by current new build regulations.

Newer double glazing technology featured optimised window cavities (closely measured gaps between each pane of glass), the use of advanced coatings to reduce heat transmission, and an inert gas to fill the cavity to reduce energy loss. It’s an improvement, but still a way to go before bringing the U-value to somewhere near the wall.

The next innovation has been triple glazing where a third pane of glass is used to further insulate and reduce heat transmission. Generally, triple glazing brings the U-value down to around 0.8 – still not a match for a wall but much closer than before.

Window and door technology

Along with the glazing, the technology of the window and door design matters a great deal. Well insulated frames make a big difference; the older, metal frames in themselves lose a lot of heat by conducting it through and out of the building while more modern solutions retain heat better.

Close fitting doors and window openings prevent heat loss compared to an inferior design, and it’s possible to specify energy efficient yet stylish doors and windows for a conservatory or other structure such as an indoor swimming pool or winter garden. Designs such as Solarlux bi folding doors offer the opportunity to have an airy, fully glazed yet energy efficient space with options such as triple glazing and heat insulating glass.

Energy ratings

One downside to purely judging window efficiency on the U-value is (in the case of new build homes and extensions) the tendency for builders to fit smaller windows to fall within accepted U-value limits. This obviously reduces the amount of light able to get into a room and the window’s solar gain potential as there’s a smaller overall surface area, therefore it’s better to judge a window by its overall energy rating.

The Glass and Glazing Federation (GGF) rate glass based not just on the U-value but on overall solar gain benefits using a ‘rainbow’ energy efficiency labelling system similar to that used on appliances such as fridges. At a glance you can see how energy efficient a type of window will be; the window’s U-value is clearly stated.

Further information on energy efficient windows, how to select them, calculating your potential energy savings and a sample of the ‘rainbow’ labelling system can be found on the GGF website.

Should you switch from single to double, or double to triple glazed windows?

In all likelihood you’d not ‘get your money back’ in changing windows from double to triple glazed although you’d probably notice a difference in heat use (not having the heating on as often and being able to run it at lower temperatures at times). You’d also notice a sound insulation difference if, say, you live near a busy road.

If you’re replacing single glazing, then doing so with triple as opposed to double glazing would be worthwhile, however.

Other options

You may not be able to use triple or even double glazing in some circumstances – perhaps you live in a conservation area or listed building? If so other options such as secondary glazing and certain types of curtains and shutters may be open to you.

Quality as a priority

While the latest glazing technology such as triple glazed glass may be the answer if newly glazing a conservatory or other structure – or replacing old single glazing – the key is to invest in designs with a high standard of construction.

Doors and glazing designed for certain applications such as a conservatory, balcony glazing or similar that fit well with top quality opening and closing mechanisms such as in the Solarlux brand mentioned above will do the best job in keeping as much heat in as possible.