Window locks - sliding sash

Good qualty locks fitted to all windows is an important safeguard for the overall security of your home. They are simple to fit and the time taken is well worthwhile. As with all key operated locks, do not leave the key in them or on display but do make sure all members of the household know exactly where they are in case of emergency.

Sliding sash window lock

The most usual and very effective type of lock for sliding sashes is the dual screw. A metal barrel is inserted into the inner sash and either another metal barrel or a lock plate fitted to the outer sash. The bolt is inserted and screwed into place using a key

Fitting the dual screw lock

It is usual to fit two of these locks on sliding sask windows unless they are small. With the window in the closed position, mark the position of each lock on the horizontal rail of the inner sash. Then mark the half way point between the top and bottom of this rail at these positions. Before drilling, double check that the hole will not catch and crack the edge of the glass. If needs be, offset the lock slightly to clear the glass.

Using a drill bit of the recommended diameter, drill into the inner sash and on into the horizontal rail of the outer sash. The depth of the hole in the outer sash will be detailed with the lock, but this will usually be around 18mm. In order to avoid overdrilling, use a depth guage mounted on the drill and set to the required overall depth. If you don't have one of these, simply wrap a small piece of tape around the drill bit at the right depth and stop when the tape reaches the surface. Open the sashes and clean out all the residual sawdust. A vacuum cleaner does an excellent job of clearing this.

Insert the barrel for the inner sash into the hole and tap it home so that it is flush with the surface. Use a small block of wood on it so as to prevent damage from the hammer. Some windows - particularly older ones with thinner glass can be quite fragile. For these, you can push the barrel into the sash by holding a clamp around the two and tightening it till the barrel sits flush. Repeat the process with the outer shorter barrel

Close the window sashes and insert the bolt into the barrels and use the key provided to secure it. Depending upon the lock and the window sizes, it may be necessary to shorten the bolt. This can easily be done by holding the bolt in a bench vice and trimming with a hacksaw.

Sash window push lock

These are very simple devices consisting of two surface mounted metal plates with a push lock mechanism between the two and requiring a key to release. Fitting is very straightforward. Simply hold the two sections together in the locked position and place on the horizontal rails where the two sashes meet making sure that the dividing line between the two aligns with the meeting line of the inner and outer sash.

The plates are then simply screwed into the sashes using the screws provided. This type of lock is a little less secure as the screws are visible making them easier to remove. However, they are quicker and easier to lock and unlock than the dual screw bolt and afford a reasonable degree of security.

• Window locks - casement
• Windows - sash repairs