Approximately 10% of the total heat loss from a typical house is through the windows. Secondary glazing can be a cost-effective way of reducing this heat loss and making your home more comfortable.
For some people, replacing old single-glazed windows with modern double-glazing is not an option. This may be 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 around £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, is the option to fit a sheet of rigid and transparent material like clear acrylic plastic or clear polystyrene to the window frame in such a way that it can be put up or taken down as the season requires. Some systems use magnetic 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.
A 3mm sheet of acrylic of around 150×100 cm costs upwards of £70 plus VAT.
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,
The savings from this type of secondary glazing are on average: £310 a year for a detached house, £168 for a semi, £150 for a mid-terrace house, and £74 for a mid-floor flat (figures taken from the National Housing Model).