If you are going to install your own double glazing, it is likely you will choose a DIY type since kits for these are widely available and are relatively easy to install. There are, however, a number of problems you may come across when fitting them.
For example, they can be fitted to existing timber or metal window frames; but if metal frames are fixed directly into masonry, you will have to drill and tap the frame to provide screw-fixing points or fit a secondary timber frame to accept the double glazing, particularly if the frame is too narrow. However, most metal windows are set in a timber surround and this can be treated as the window. If you want to fix the double glazing frame to the reveal, you may come across the problem of an out of square reveal; to deal with this you will have to pack the out-of-square area with timber wedges or choose a system which fits directly to the window. Again, certain types of kit require the channels in which the new glazing is fitted to be mitred at the corners and joined. If you think you will find this too much of a problem, choose a type which is supplied with corner pieces.
Remember to cut the channel lengths squarely at the ends or you will find it difficult to fit on the corner pieces and the final appearance of the glazing will be marred. Also, don’t expect the glass to be a push-fit into the channel; it might slide in, but often you will need to encourage this by tapping gently with a mallet or with a hammer and a block of wood placed to protect the glass. Warning If you are going to double glaze bay windows, remember to treat each window as a separate unit. There are many makes of secondary sash double glazing available and the manufacturers supply detailed instructions for installation.
There are, however, three basic types of system: plastic channel, fixed or hinged, and sliding secondary sashes.
With this type, each pane of glass is fitted into a frame made by cutting lengths of U-shaped plastic channel to size; remove any sharp edges from the glass with a carborundum stone. The corners of the channel have to be mitred. Using a sharp knife and a mitre guide, cut the first mitre corner and then fit the channel to the glass to determine the position of the second corner. Remove the channel and mitre-cut at this position; repeat this process until all four corners have been cut. Secure the channel to the glass; some kits require the use of adhesive to form a rigid frame. Hold this assembly up to the window and fix it in place on the frame with the plastic clips supplied with the kit. With this type of double glazing, out-of-square reveals will not cause problems since the channel is always fixed to the frame.
Fixed or hinged
Usually this type consists of plastic or aluminium channel cut to shape and joined at the corners by mitring or by using special corner pieces. Fixing is either by clips to non-opening windows or by hinges to opening windows (the new windows can be hinged to open sideways or upwards). You could, of course, use hinges with fixed windows to make them easier to clean. This type of double glazing will, if correctly assembled, eliminate draughts and the new windows can be removed for summer storage. Before you buy this type of system, read the manufacturer’s instructions carefully to check the frame around your window is wide enough to take the double glazing and that it is made of the right material to take this particular system. With some systems the manufacturer recommends fixing only to wood rather than metal frames. Again. your existing window catches or handles may protrude in such a way they will interfere with the installation of the new system. You can usually solve these problems by fitting a secondary timber frame to take the double glazing; butt-join the corners of the frame, fill in any gaps with wood filler and apply a wood primer followed by two coats of paint. allowing the first coat to dry before applying the second. There is one system which uses PVC shatterproof panels instead of glass. These are fitted into self adhesive plastic tracks which are cut and pressed into place to the wall outside the reveal. The panels can be easily removed, but you may consider this too much trouble with opening windows.
Usually this type is fitted in the reveal. An outer frame is fixed in the reveal to square up the opening; use pieces of wood as packing if necessary. The glass is fixed in a separate frame which is fitted inside the outer frame to enable the glass and its separate frame to slide. The framed glass is removable and horizontal and vertical sliders are available. Depending on the size of the window, two or more sliding panels will be needed. One system can be fixed to the face of the window frame so you will avoid the problems of squaring up a reveal, although it can be reveal fixed as well. In this case the company offers a kit specially designed to suit your windows; it comprises plastic channelling cut to size and ready to be joined on site so no cutting or mitring is required. The glass comes complete in its tailor-made frame ready to be installed in the channelling.