The door should be fitted with a 5 lever 2 bolt mortice sash lock halfway up the door, (a deadlock with a handle for convenience). Unlike front doors, many insurance companies do not specify that they should be to British Standard 3621 or equivalent European Standard EN 12209, though the use of this standard of lock is recommended.

The sash lock should be supplemented by mortice rack bolts (bolts fitted approximately 150mm (6") from the top and bottom of the door into the wood and operated internally) or surface-mounted locking bolts top and bottom. They should always be fitted at 90º to the grain of the wood, reducing the likelihood of the wood splitting if subjected to pressure.

Any glass panels should be laminated and fitted from the inside to prevent the putty or beading being removed. Grilles could also be fitted to the inside of the panels.

French doors

Also known as French windows, they are intrinsically less secure than single leaf doors, which may reflect on their comparative lack of popularity as compared with the modern patio door. However, this need not be the case provided that suitable security measures are taken.

Both doors should be fitted with mortice rack bolts (bolts fitted within the door and operated internally by a threaded key). They should always be fitted at 90 º to the grain of the wood, reducing the likelihood of the wood splitting if subjected to pressure. Alternatively, use surface-mounted locking bolts (push to lock, key to open). Whichever type you use, fit top and bottom to provide rigidity.

If the style of door is capable of it, a mortice sash lock can be fitted for extra security (rebate sets may also be required).

As most French Doors are outward opening, the addition of hinge bolts is also recommended. They should be located 100-150mm (4-6") below the top hinge and similarly above the bottom.

Note: It would be acceptable, for insurance purposes, for key operated bolts only to be fitted top and bottom of both doors.

Consider replacing ordinary or toughened glass panels with laminated glass - two pieces of glass bonded together with a sheet of laminate - as they offer much greater resistance to attack.

UPVC/PVCU French doors are generally unsuitable for retro-fit security devices. Not only is the material not strong enough to support devices fitted with steel screws unless secured into the internal metal framework, but such changes to the original design may invalidate an existing warranty or possibly damage the integral locking assembly. If in doubt, consult the installer/manufacturer. Modern designs will usually incorporate deadlock shoot bolts or a multi-point locking system, both throwing a number of bolts from the door into the frame. Under these circumstances there will not normally be any need for additional devices.

Patio door

Entry through a patio door is a common means of entry and therefore, unless the doors are fitted with a multi-locking system, it is best to fit extra locks. These are fitted on the bottom fixed frame pushing through to the sliding frame in the centre and on the side frame at the opening point no lower than a third of the way from the top of the door. Most such locks are push to lock and key to open and are therefore easy to use. Make sure there is enough frame to fit them on if drilling is required. If in doubt, consult the installer or manufacturer.

A dual screw can be fitted between both frames but it is more awkward to use, so there can be a tendency to leave it unlocked, thus defeating the object. An alternative would be to fit long-throw bolts top and bottom of the opening door.

Some patio doors can be lifted off their track. If you can lift it more than 1/4" simply screw wood blocks of a suitable depth into the channel above the opening door to prevent this. Alternatively, anti-lift devices are available from locksmiths.