How to Fit Double Glazing

Exactly how much heat double glazing will save is debatable; much depends on the number, orientation and size of the windows. It is generally estimated that about 10-15 per cent of heat goes out through the windows of the average house and that this can be halved with an efficient, well-installed system.

Double glazing is not a short-term invest­ment. Its initial cost will take many years to recover. However, it will make the house much more comfortable by reducing drafts and cold areas around the windows.

Whereas most people install a system to reduce heat loss, in some cases insulation against unwanted outside noise is the main objective. For thermal insulation, an optimum gap of 3/4in is needed between the two panes of glass, whereas for good sound insulation the gap should be about 4in.

Assembling & fitting

There is generally no problem in fixing the double glazing frames to an existing wooden framed window; metal frames, however, are more awkward. If the system you chose is suitable for fixing to metal, then you will need either self-tapping screws or you will have to heir install a secondary wooden frame around the window on which to mount the system.

It is a relatively straightforward job mounting the double glazing directly on to the window frame. Fixing it into the window reveal, where necessary, can be quite difficult, since rarely will a window reveal be exactly square. But it is essential to ensure your secondary frame is perfectly square if the panels are to slide, hinge or close properly.

Check the existing handles and stays. If they project too far, they will prevent you fitting your system to the window frame. If you do not want to fix the glazing to the window reveal, then you will have to change them.

The different systems are all assembled and fitted in a similar way. Bear in mind, however, that if you want a hinged system, you will need to construct a wooden framework on which to mount the secondary glazing and then hang the whole assembly on brackets fixed to the window frame.

Provided both the existing window frame and the double glazing you have put up are both well sealed, the problem of condensation between the two layers of glass can largely be avoided. A point worth noting is that it is advisable to install your system on a day when the air in the room is cold and dry. If damp air is trapped inside the cavity, inter-pane misting will be a constant problem in the future.

Storm windows

The other common form of energy-saving for windows is the aluminum storm window. These are custom-made by specialist companies who work on site and fabricate each window to fit the exact dimensions of the window over which it will be fitted. They are generally made to match the existing window style as closely as possible, and come equipped with an integral insect screen for use in summer when the windows are open. The frames can be painted to blend in with the existing window trim.