In many cases it is not possible to retro-fit any extra locks to UPVC windows. This is because the material used is not strong enough to support a metal lock fitted with steel screws. It could also damage the window and perhaps invalidate any existing warranty.
Double glazed window locking systems should be fitted at the time of manufacture. A general rule to follow is that the handle should not be the only means of keeping the window closed. The locking system should be fitted within the framework and the handle is used as a means of throwing or engaging the internal locking system.
Always consult the manufacturer/supplier before attempting to fit any extra locks. There are locks that can be fitted to UPVC casement windows, but only if there is no integral locking system within the framework, typically where the only means of security is a locking handle.
There are two main types of locking systems:
—-The first is espagnolette (multi-point) locking, which are bolts (normally 3 sets) set into the window and located into locking points in the frame when the handle is turned. The bolts should be mushroom headed so that they can engage behind the locking point, thus enabling the window to resist being forced apart from the frame.
—-The second type is deadlock shoot bolts which locate into the frame at both opening side corners. There is also a deadlock which secures the opening side of the window at the handle.
For additional strength sections of hardened aluminium or galvanised steel reinforcements should be fitted at the time of manufacture within the hollow profiles of the windows and frames, so that the locking systems can be secured through the UPVC frames into the reinforcements.
It is preferable for the windows to be fitted with internal beading to avoid the possibility of the glass being removed from the outside. There are some systems which have external beading but are secure because the glass is adhered to the frame or secured by special tamper-proof clips, but in most cases internal beading is preferable.
Lastly, if you are considering replacing your existing windows, look for the new British Standard 7950 kite mark. It has been established to set specific manufacturing standards of design and security for windows.