Do I need a key-operated lock?

When it comes to windows, locks must be key-operated. Even if a window has been painted shut, it must have a lock to satisfy insurers.

They will normally specify that any window on a ground or lower ground level, in addition to any accessible windows on upper floors (via a flat roof, cast iron drainpipe, tree and so on), should have adequate security measures.

Find a Which? Trusted Traders accredited locksmith in your area, or read on for more tips on securing your windows.

Should I choose a wooden casement window?

For wooden casement windows (hinged on the left or right and outward opening), avoid locks which only secure the handle and instead choose casement locks which secure the together the window and frame. These give an additional point of resistance in the event of someone attempting to prise or force the window open.

Where the window is flush to the frame, fit key-operated mortice rack bolts.

If you're considering replacing casement windows, look for the British Standard 7950 Kitemark – a specification for enhanced security performance of domestic casement windows.

Are wooden sliding sash windows secure?

Bars, clasps and fasteners are not treated as locks.

A pair of sash stops is the best way to secure the window. Apart from preventing the windows from being forced upward, they can also be used to lock a sash window open for ventilation. As they’re visible from the outside, sash locks also act as a visual deterrent.

Dual screws are an alternative although they are fiddly and not as effective as sash stops.

How useful are tilt-to-clean sliding sash windows?

In addition to sliding up and down, these modern windows can be tilted inward for cleaning. Secure them with a combination of sash stops and dual screws.

Are uPVC windows safe?

uPVC windows are manufactured with an insurance standard multi-point locking system which engages a number of mushroom-headed bolts into a plate when the handle is turned.

Further measures are not needed as uPVC windows are very secure.

Metal crittal windows

The window or handle can be secured with specialist locks to prevent opening. A fanlight lock should be used on a fanlight crittal window.

What use are window security grilles?

If you need a high level of protection, you could fit a window grilles. These act both as a visual deterrent and a physical barrier against entry. Decorative grilles are available.

Glossary of locksmithing terminology

  • Dual screw: A key-operated lock which bolts two sash window frames together to prevent opening.
  • Lever: The movable part in a lock. The levers are moved by the key to operate the lock. The 'five lever' lock is often an insurance requirement.
  • Mortice lock: A mortice lock is one which requires the mechanism to be cut into the door, window or piece of furniture which is being fitted with a lock.
  • Rack bolt: A type of bolt with ‘teeth’ which is operated only from the inside. The bolt is extended with the turn of a toothed key.
  • Sash stops: These are fitted to the top of a sash window to restrict how far the window can be opened.

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