What is the difference between a mortice sashlock and a mortice deadlock?
Two locks that look identical in a catalogue and do different jobs — which door each belongs on, what the lever count means, and what an insurer is actually asking for.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
A sashlock has a sprung latch as well as a deadbolt, so the door holds shut on a handle and locks with a key. A deadlock has only the deadbolt and no handle, so the door needs something else to hold it shut. Front doors with a nightlatch take a deadlock; back doors and internal doors that need a handle take a sashlock.
Both are mortice locks: a steel case let into a slot cut in the door edge. The only difference is whether there is a latch in the case as well as a bolt, and that single difference decides which door each one suits. Getting it wrong produces either a door that will not stay shut or a handle with nothing to operate.
Step by step
- Look at what holds the door shut now.If the door closes and stays closed on its own, something sprung is holding it — a latch inside a sashlock, or a separate nightlatch on the inside face. If the door swings open when you let go unless it is locked, it has a deadlock and nothing else.
- Choose a sashlock where the door needs a handle.Back doors, side doors, garage personnel doors, and any internal door that needs to be lockable. The latch means the door holds shut with the handle, and the key throws a separate deadbolt when you want it locked.
- Choose a deadlock where something else already latches the door.The classic British front door has a nightlatch high up, which holds and latches the door, and a mortice deadlock lower down for a proper key-locked bolt when the house is empty. A deadlock alone on a door with no nightlatch will not stay shut.
- Understand the lever count.Mortice locks are described by the number of levers in the mechanism — commonly three or five. More levers means more key differs and more resistance to manipulation. Three-lever locks are for internal doors and low-risk situations; five-lever is the domestic external standard.
- Check whether it meets the insurance standard.Insurers typically specify a mortice lock made to the relevant British Standard for thief-resistant locks, which is marked with a kitemark and the standard number on the faceplate. It is not simply a lever count — a five-lever lock without the marking may not satisfy a policy.
- Read your own policy wording rather than a rule of thumb.Requirements vary between insurers and between policies. The wording usually appears under the security conditions, and it will say what the final exit door and other external doors have to have.
- Check what will fit before buying.The new lock has to suit the existing mortice, or you have to be prepared to cut a bigger one. Case size, backset and the position of the keyhole all matter.
- Consider the handing and the escape question.A deadlock that is key-operated from both sides means nobody leaves without a key. On a final exit door that is a genuine trade-off against escape, and it is the reason many households keep the key on a hook beside the door, always in the same place, out of reach of the letterplate.
Alternatives
- Mortice sashlock: Latch plus deadbolt, operated by handle and key. The general-purpose external and internal lockable door lock.
- Mortice deadlock: Deadbolt only, no handle. Pairs with a nightlatch on a front door, or secures a door that is bolted rather than latched.
- Mortice latch: Latch only, no lock and no key. What most internal doors have — a handle to hold the door shut and nothing more.
- Bathroom mortice lock: A sashlock with a thumbturn instead of a keyhole and an emergency release on the outside. The correct choice for a bathroom or WC.
- Euro-profile mortice sashlock: A mortice lock that takes a euro cylinder instead of a lever key. Useful where a timber door needs to be keyed alike with uPVC doors.
Questions people ask
Can I fit a deadlock in place of a sashlock?
Physically, sometimes — but the door then has no latch and will not stay shut, so it only makes sense if you are also fitting a nightlatch or bolts.
Is a five-lever lock always better than a three?
For an external door, yes, and most insurers expect it. For an internal door a three-lever lock is entirely adequate and cheaper.
What is a 'BS' lock?
Shorthand for a lock manufactured and independently tested to the British Standard for thief-resistant mortice locks. Look for the kitemark stamped on the faceplate, not on the box.