Types of double glazing
There are four types of double glazing in common use: insulating glass, secondary sashes, coupled windows and plastic film.
Insulating (hermetically sealed) glass
These units look like a single pane of glass and consist of two pieces of glass joined together and hermetically sealed in the factory – a process in which the air space between the panes is dried to prevent misting when installed. The pieces of glass are sealed with edge spacers of metal, alloy or plastic. The units are tailor-made and replace a single pane, enabling a window to open and close normally. There are two types standard and stepped. The stepped units are ideal where there are shallow rebates since installation can be carried out without having to alter the existing frame to accept the new units. The existing frame must be well fitting and sound enough to take the extra weight which will be imposed by the units.
Secondary sashes
This is the most popular DIY method of installing double glazing. A second pane of glass in its own frame is secured to the existing frame or to the inner or outer sill and reveal; in some circumstances it is possible to flt the new window outside the existing frame. The existing window remains unaltered to form the other half of the double glazing. Manufacturers supply frames of aluminium or plastic; other types consist of plastic extrusions which are cut to length and joined with corner fittings to enable a frame for the glass to be made up. Hinges or clips are then used to secure the secondary sash to the existing window. The secondary sash is movable for cleaning, ventilation or summer storage and can be fixed, hinged or sliding.
Coupled windows
These are usually specified only for new buildings or where entire frames are being replaced during conversion. One single-glazed window has an auxiliary window coupled to it, allowing both to move together. They are flitted with hinges and fasteners so the frames can be separated for cleaning purposes.
Plastic film
This is not double glazing in the traditional sense, although at least one proprietary system is available. Plastic film is cut to size and applied to the window frame with double-sided adhesive tape. If you use this method, make sure that where windows are to be opend they are double-glazed separately from fixed panes; if a complete film was stretched across the entire window it would not be possible to open the window without first removing the film. If you are restricted to a very small budget, you can use kitchen self-clinging plastic to make a form of double glazing for small panes. For larger panes, you will have to break up the pane space with a thin timber framework to create the effect of smaller panes and fix the film inside these smaller areas.