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Secondary glazing

Around 18% of the total heat loss from a typical house is through the windows. By reducing window draughts you can cut the heat loss and make your home more comfortable

For some householders replacing old single-glazed windows with modern double-glazing is not an option. This may due to the cost involved, or because the house is listed or in a conservation area where original features like sash windows have to be retained. 

However it is still possible to cut out the draughts and reduce heat loss through windows using various forms of secondary glazing. Some can be bought from your local hardware store and fitted yourself; others are more specialist. Some of the secondary-glazing options listed below are not allowed in listed buildings, so check first.

Transparent film secondary glazing

The simplest and cheapest form of secondary glazing is thin transparent plastic film which you install yourself using strips of double-sided sticky tape around the frame of the window. The material looks like ‘cling-film’, but if fitted properly it is wrinkle-free and almost invisible. To install, apply the tape to the frame of the window, cut the film to size and attach it carefully to the tape until it creates a seal. Then carefully shrink the film with hot air from a hairdryer until it pulls taught, and trim any excess film from around the edges.

Enough film to cover a large bay-window costs £10-15 and is available from DIY stores. The film is simple to remove, though doing so can damage the window's paintwork.

Temporary secondary glazing

Next up, in terms of expense, complexity and permanence are the systems in which a sheet of rigid and transparent material like clear acrylic plastic or clear polystyrene is fitted to the window frame, in such a way that it can be put up or taken down as the season requires. Some systems use magnet strips to attach the secondary glazing to the frame, others a Velcro-like material. A particularly popular method is ‘clip and stick’ where uPVC edging is used to clip the panel in place over the window frame.

This type of secondary glazing also helps reduce noise.

Semi-permanent secondary glazing

Some of the more expensive types of secondary glazing are semi-permanent and are fixed either by screwing them into place or using a strong adhesive or sealant. They can be made of heavy materials like glass. On wider windows they can slide open on tracks to allow the windows to open as normal. This type are not generally suitable for DIY.

Sash windows are notorious for letting in cold air. You can get clear, light-weight acrylic panels to fit over the glazed frames, but these don’t cover the many gaps on the sides, top and bottom that make sash frames particularly draughty.

Frequently asked questions

What is low 'e' double glazing?

Low emissivity (low E) double glazing incorporates a very thin layer of metallic coating on one surface. This coating allows the sun's heat to enter the building but significantly reduces heat loss from the building by reflecting radiant heat back into the room.


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What are trickle vents?

A trickle vent is a small adjustable opening in a double glazing unit that allows a small amount of ventilation in rooms that are double glazed. This is required because fitting double glazing reduces the amount of natural (or passive) ventilation in the home.


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Why does condensation appear on my windows?

Air contains varying amounts of water vapour. Warm air holds more water as vapour than cold air. If warm moist air is cooled by a cold surface like a window pane it will not be able to hold the same amount of water vapour, therefore the water turns into droplets of liquid and collects on the cold surface as condensation.


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