What is a Sash Lock?

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This post is part of our regularly reviewed content series, ensuring all advice remains accurate and relevant to your home project.

Author: Carl Benson

Carl is the founder of Suffolk Latch Company, with a background in engineering and over 20 years’ experience in home hardware. He works closely with suppliers and designers alike to develop quality ironmongery that stands the test of time. Read my full bio.

Carl Benson

Introduction

“A sash lock combines two functions in one case: a latch to hold the door closed and a deadbolt to lock it.”

A sash lock is a door lock with a handle-operated latch and a separate locking deadbolt in one case. Usually morticed into the edge of the door, it holds the door closed when unlocked and allows it to be locked with a key or thumbturn, depending on the model.

Also written as sashlock, it is different from a sash-window fastener. This guide explains door sash locks, their main parts and how to choose matching handles.

Sash locks, deadlocks and tubular latches

These names describe different arrangements:

  • Sash lock: a latch and deadbolt within one case.
  • Deadlock: a locking bolt without a handle-operated latch.
  • Tubular latch: a handle-operated catch without a locking deadbolt.

Mortice describes fitting the mechanism into a recess in the door. Both sash locks and mortice deadlocks belong to this wider family. A deadlock may be used alongside a separate latch where the door needs both functions.

Antique Brass 3 Lever Sash Lock - 2.5 Inch

Antique Brass Bathroom Sash Lock - 2.5 Inch

The parts of a sash lock

  • Case: the body containing the mechanism.
  • Latch bolt: the spring-loaded catch operated by the handles.
  • Deadbolt: the bolt operated by the key or thumbturn.
  • Forend: the plate visible on the door edge, through which the bolts project.
  • Strike plate: the plate on the frame, also called the striker or keep, with openings to receive the bolts.
  • Follower: the square opening that accepts the handle spindle, also called the mortice bar.

How a sash lock works

With the deadbolt withdrawn, pressing the handle retracts the latch so the door can open. As the door closes, the bevelled latch passes the strike plate and springs into its opening.

Operating the key or thumbturn extends the deadbolt into the keep. On a conventional sash lock, pressing the handle alone does not withdraw this bolt. Some escape-function locks operate differently, so check the instructions for the particular mechanism.

Types of sash lock

“The term ‘mortice’ describes how the lock is fitted, while ‘sash lock’ describes its latch-and-deadbolt arrangement.”

Three-lever sash locks

These use a key-operated lever mechanism and are commonly chosen for internal doors needing a basic lock. Our 2.5-inch three-lever sash lock is one example. Do not assume an internal lock meets entrance-door security requirements.

Five-lever sash locks

These have five levers in the locking mechanism. Some are certified security locks, but lever count alone is not certification. Our 2.5-inch five-lever mortice lock is specified as BS 3621 Kitemarked.

Bathroom locks

A bathroom mortice lock uses a separate turn to operate the privacy bolt. Choose a compatible turn-and-release set so it can be released from outside in an emergency. Check its spindle size and centres; these are not universal.

Euro-profile sash locks

These use a separate euro cylinder rather than a traditional lever key. Euro-profile describes the cylinder format, not whether the case includes a latch. Check the mechanism within our Euro Profile Locks collection: a euro sash lock and a euro deadlock serve different purposes.

Matt Black 3 Lever Deadlock - 2.5 Inch

Matt Black 5 Lever Deadlock - 2.5 Inch

Choosing a lock and matching handles

“Matching a sash lock involves more than checking its case size. Backset, centres, spindle and fixing positions must also agree.”

Start with the door’s purpose: simple latching, bathroom privacy or security. Then compare the exact lock drawing with the door and proposed handles.

  • Case size and backset: these are separate measurements. Backset locates the spindle relative to the door edge; case size describes the body.
  • Centres: match the spindle-to-keyhole, cylinder or bathroom-turn measurement where using a fixed backplate.
  • Spindles: check the specified cross-section, length and engagement for the door thickness.
  • Fixings: check screw positions and any permitted bolt-through openings. Never drill through a lock case to make a handle fit.
  • Springing and handing: confirm handle compatibility and latch orientation with the manufacturer. Only reverse a latch using its specified method.

Sprung handles have their own return spring; unsprung handles depend on a suitable return mechanism elsewhere in the assembly. A lock’s latch spring does not automatically make it suitable for every unsprung lever.

Use our backset measuring guide for the measuring points. Check these details before choosing the style and finish from our Door Handles collection.

Security and fire-door suitability

“Lever count, security certification and fire-door suitability are separate considerations that must be checked for the exact lock.”

Security certification

For an entrance door, check the exact lock’s security certification and your insurance requirements. The Master Locksmiths Association’s BS 3621 guidance explains why five levers alone are insufficient. A bathroom privacy lock is not a substitute for a security lock.

Where escape without a key is required, have the appropriate lock specified by a competent professional.

Antique Brass Euro Deadlock - 2.5 Inch

Antique Brass Euro Sash Lock - 2.5 Inch

Fire-rated locks

Fire performance and resistance to forced entry are separate matters. Fitting a fire-rated sash lock does not turn an ordinary door into a fire door.

The exact lock must be permitted by the fire-door documentation and installed with any required intumescent protection. Do not transfer a rating or fitting detail from another model. The BWF Fire Door Alliance explains compatible hardware requirements.

Our Certifire information for locks and latches provides supporting documents. Match the product reference and certificate conditions to the intended installation.

Conclusion

A sash lock provides everyday latching and a separate locking bolt. Choose the mechanism for the door’s purpose, then check dimensions, handle compatibility and any security or fire-door requirements. Browse our Sash Locks collection once those requirements are clear.

Satin Brass Horizontal 3 Lever Sashlock - 6 Inch

Polished Chrome Magnetic Bathroom Sashlock

FAQ

Is a sash lock the same as a mortice lock?

A mortice sash lock is one type of mortice lock. “Mortice” describes its recessed installation; “sash lock” identifies the latch and deadbolt arrangement. A mortice deadlock has no handle-operated latch.

Does a sash lock automatically lock when the door closes?

A conventional sash lock latches when the door closes, but its deadbolt must be operated separately. Check the instructions if the lock has an automatic or escape function.

Will any door handle fit a sash lock?

No. Check the spindle, springing, fixing positions, door thickness and any backplate centres against the exact handle and lock specifications.

Can I replace a sash lock with one of the same case size?

Not on case size alone. Backset, centres, forend, strike plate and fixing positions may differ. Any required security and fire-door approvals must also remain appropriate.

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