Up to 15% of the heat loss from a house can be through the windows. Double glazing can halve this loss, although the cost can be considerable, especially if you choose commercially installed sealed-unit replacement windows. However, with a low-price DIY system you may be able to get your money back in five to 15 years, depending on the fuel used and the size of the windows. You should also take into account the additional comfort provided by double glazing, the extra noise insulation, better security and the greenhouse effect which helps to heat the rooms on any sunny day, even in winter.
When installing double glazing, pay special attention to the following points so that your windows can be used in an emergency if the usual means of escape is cut off.
1. Do not install a fixed, sealed double glazing unit unless there is an adjacent opening window (not a fanlight). Secondary sash units should have at least one sliding or hinged pane.
2. Always glaze opening sashes or casements separately.
3. To give sufficient warning for a safe exit to be made by the usual means, fit a smoke detector on every level of the dwelling and
interconnect them to ensure an effective alarm, even if you are asleep.
4. If you are in any doubt about fire precautions, contact your local fire prevention officer and ask his advice. The telephone number is under the name of your local county council, fire brigade department, in your local directory.
Remember, the benefits of heavy lined curtains for window insulation. These are effective at reducing heat loss in the evenings and at night, and they may be preferable to double glazing if the room is not heated by day and only in the evenings. The benefits of curtains are enhanced further if they are backed by aluminium foil reflective loose linings (known as Milium).
This is the very simplest form for double glazing and is ideal where a low-cost temporary system is required. For windows with small panes, such as the Georgian style, self-cling kitchen film can be applied directly to the frames. If these have been recently painted, the film will cling perfectly. Larger frames can be treated in the same way if a light timber framework is made up to divide the frame into areas in the Georgian style.
Another method is to double glaze the window with clear plastic film, or even clear polythene sheet as a low-cost alternative. The plastic sheet can be held to the frame using double-sided adhesive tape. Opening windows should be double glazed separately from the fixed frames so that the windows can be used without removing the film. Make sure the windows are draught-proofed or the film will move noisily in the wind.
Thick, clear, rigid plastic sheet is cheaper than glass and much quicker to fix, but care must be taken in cleaning to avoid scratching the surface. The cheapest type is clear polystyrene, but the more expensive acrylic (Perspex) sheet will not yellow in normal use.
Plastic sheet can be fixed with double sided adhesive tape, although the sheets are very difficult to remove for cleaning. Another system uses self-adhesive plastic channel on the window frame into which the sheets are clipped. The best system uses two-part self-adhesive magnetic strip around the perimeter of the sheets to hold them to the window, yet allow them to be removed easily for cleaning. All these self-adhesive systems are ideal on metal frames.
These hermetically sealed units consisting of two panes of glass are normally fitted in replacement window frames, but they are available for replacing a single pane win-
V-shape cuts are made in the corners to form neat mitres. Plastic clips hold the glass and channel assembly to the window frame. Treat frames individually so that opening windows can be used, and large sheets are avoided which otherwise may crack when the panels are unclipped for cleaning.
Secondary sash double glazing kits
These are the best forms of d-I-y double glazing in which standard 4mm glass is held in rigid plastic or aluminium frames which are attached to the existing window frame, or to the inside of the window recesses and sills. The units may be fixed (for non-opening windows), hinged, or sliding (for horizontal or vertical sliding sash windows). Of course, hinged units can be used on fixed windows to make cleaning easier.
The secondary sashes are usually fitted on the insides of the window, but some systems can be fitted to the outside of the frame where this is preferred.
Before buying a double glazing kit, measure up the windows very carefully to ensure that the kit is the right size and of the right type for the particular window. Also be very careful to use glass of the correct thickness, and cut to the right size (the manufacturer’s fitting instructions tell you how to measure). Check after fitting that the sashes butt tightly against the frames to reduce the risk of condensation forming between the frames.
Although secondary sashes reduce draughts caused by poorly fitting windows, for the maximum effect, the windows should be properly draught-proofed at the time the double glazing is fitted.
With metal windows, the secondary sashes are best fitted to the main timber frame. It is a very efficient system.
There are two types of insulating glass units — standard and stepped. The stepped units can be fitted in a conventional frame without alteration to the depth of the glass rebate (step). The frames must be in good condition to make the expense and effort of replacing the glass worthwhile. The benefit of this double-glazing system is that the appearance of the window is unaltered. But the insulating properties are greatly enhanced.
Plastic channel and glass
This very simple secondary glazing system uses flexible U-shape plastic channel which is simply cut to length and fitted over the edge of a sheet of glass to provide a neat edge and a tight seal when the glass is pressed against the window frame.