Deadlock, Deadbolt or Sash Lock: Which Do You Need?

What is the difference between a deadlock, deadbolt and sash lock? If you are fitting a new internal door and want it to lock, you may need one of these options.

Choosing the right mortice lock can be confusing, so this guide explains what each type does and where it is normally used.

Mortice Deadlocks

A mortice deadlock is fitted into the timber edge of a door and allows the door to be manually locked from both sides with a key.

A deadlock contains a lock bolt only. It does not include a latch or catch for operating a door knob or door handle.

Deadlocks are commonly available as either 3 lever or 5 lever locks. When choosing the right deadlock, you will also need to select the correct case size and backset for your door.

A standard deadlock usually has a 3-inch case with a 57mm backset. The backset is the distance from the edge of the door to the centre of the keyhole.

5 Lever Deadlocks

Five lever deadlocks are commonly fitted to timber front and back doors. They are often required by home insurance providers because they offer a higher level of security than 3 lever locks.

When choosing a 5 lever deadlock for an external door, look for a lock that is kitemarked to British Standard BS3621.

3 Lever Deadlocks

Three lever deadlocks are intended for internal wooden doors. As the name suggests, they contain three levers, which makes them unsuitable for external doors.

They are a good choice for internal rooms where privacy is required and lockable access is needed from both sides.

Deadlocks are usually supplied with two keys, a matching forend and a striker plate in a choice of finishes. Browse the Old English Collection 3 lever deadlock.

Safety tip: keep a spare key in an easily accessible place in case of an emergency, such as a house fire.

Mortice Deadbolts

A deadbolt is usually used for locking bathroom doors and is manually operated with a turn and release.

This simple lock bolt is mortice fitted into the door and has a backset hole for the mortice bar of the bathroom thumbturn. The example shown above is a 3-inch deadbolt.

Mortice Sash Locks

A sash lock has a case body with both a latch or catch and a lock mechanism. This allows it to be used with a door handle or door knob.

Sash locks are available in different types and sizes, with 2.5-inch and 3-inch cases being the most common. These usually have industry standard backset measurements of 44mm and 57mm respectively.

The centres measurement is also important. This refers to the distance between the centre of the mortice bar fitting hole and the centre of the keyhole. The most common centres measurement is 57mm.

3 Lever Sash Locks

A 3 lever sash lock is usually used on internal doors where a handle-operated latch and a key-operated lock are both required.

5 Lever Sash Locks

A 5 lever sash lock is used when fitting a door handle to an external door and a key-operated lock is required.

When choosing a 5 lever sash lock, check that it complies with British Standard BS3621 and has the kitemark on the case body.

As with 3 lever sash locks, there are standard sizes. A common size for front doors is a 2.5-inch case with a 44mm backset and 57mm centres, as shown in the drawing above.

Euro Profile Sash Locks

A euro profile sash lock is also designed for exterior doors. It has a larger lock profile to house a cylinder lock.

This type of lock is a popular choice for front doors because the cylinder can be replaced without removing the entire sash lock from the door.

Bathroom Sash Locks

A bathroom sash lock is designed to be fitted with a door handle and a bathroom turn and release.

Like other sash locks, bathroom sash locks are available in industry standard sizes, with 2.5-inch and 3-inch cases being the most common. They have two square holes for the mortice bars of the handle and the turn and release.

You should now have a clearer understanding of the difference between a deadlock, deadbolt and sash lock. Browse our range of sash locks, deadlocks, deadbolts and tubular latches.

You can also read more fitting guides and product advice in our Ironmonger's Journal.