One of the biggest advantages of specifying mortise locks over other types of locks is the great variety of functions available. In this article I will discuss mortise locks for use in commercial / architectural applications.
Function, in this case, means how a thing works. Mortise lock functions determine how they work, the features they have, and for what applications they can be used. Knowing the features of a mortise lock and what they do can help you decide what function best suits your application.
Below is a diagram of the different features that you might find on a mortise lock:
Illustrated Mortise Lock
Mortise Lock Terms
Depending on the lock function, the lock may have any or none of the above illustrated features. Starting clockwise from upper left:
- Mortise cylinders allow the lock to be locked or unlocked from the outside by key, or for the latch to be retracted momentarily to allow entry. Sometimes they are used to lock and unlock the lock or extend or retract the deadbolt from inside as well.
- Deadbolts are extended and retracted by key or turnknob
- Keys can be used to lock or unlock the lock from inside or outside and/or extend or retract the deadbolt and/or retract the latch
- The turn knob (also called a thumb turn) is usually used to extend or retract the deadbolt, but some manufacturers (such as Schlage) use the turnknob to lock or unlock the outside handle instead of stop works
- Inside lever pictured. The inside handle, be it lever or knob, may retract the latch and auxiliary deadlatch only, or it may retract the latch, auxiliary deadlatch and deadbolt for free panic egress. Levers are the most common since they comply with ADA code.
- Inside rose trim pictured. A rose is a small finished trim plate that acts as a washer between the handle and the door.
- Stop works are used on some mortise locks to lock and unlock the outside handle.
- The auxiliary deadlatch is used on some locking functions. When the door is closed, the auxiliary deadlatch is pushed inside the lock by the strike plate, activating a deadlocking feature that makes the latch resistant to being retracted by force.
- The latch is a spring loaded, wedge-shaped device that secures the door automatically when the door is shut.
- Outside escutcheon trim shown. Mortise locks almost always have the same kind of trim inside and outside, so it would be either roses or escutcheons on both sides. An escutcheon is a large rectangular plate. They are often used in retrofit applications where there are extraneous holes to be covered.
- Outside knob pictured.
When discussing how you want your mortise lock to work with your security professional, it is helpful if you know the above terms.
Mortise lock functions are standardized in the security hardware industry, and each function has an ANSI code assigned to it. Below is a list of a few common functions:
A non-keyed function. Turning knob or lever retracts latch from either side.
A non-keyed function. Latch retracted by knob/lever from either side. Deadbolt extended or retracted by inside turnknob. Extending deadbolt locks outside lever. Turning knob/lever from inside retracts latch and deadbolt and unlocks outside lever. Can be opened in emergency from the outside by a special emergency thumbturn, coin turn.
Latch retracted by knob/lever from either side except when outside knob/lever is locked by stop works or thumbturn. Deadbolt extended or retracted by key from outside or turnknob from inside. Outside knob/lever is locked when deadbolt is extended. Auxiliary deadlatch deadlocks latch when door is closed. Inside knob/lever retracts latch and deadbolt simultaneously.
Latch retracted by key outside or knob/lever inside. Outside knob/lever always locked. Auxiliary deadlatch deadlocks latch when door is closed. Inside knob/lever always unlocked for free egress.
Latch retracted by knob/lever from either side except when outside knob/lever is locked by key. Inside knob/lever always unlocked for free egress.
A double-keyed function (keyed on both sides). Latchbolt retracted by knob/lever either side except when outside knob/lever is locked by key from inside or outside.
Latch retracted by knob/lever either side except when locked by key or stop works. When locked, latch retracted by key. Stays locked until unlocked by stop works.
Collier on July 21, 2010:
Great primer on mortise locks, Tom. I appreciate the list of ANSI function code numbers. Thanks
joseph houston from Round Rock, Texas on August 25, 2009:
OK -- What is the other lock that someone might try to sell me that I should not buy?? I think code, city ordinances and builder specs dictate locks. I beleive all locks have to abide by the code of the city or state they live in. Example- Houston, Texas does not allow double cylinder deadbolts. Good knowledge on what a lock is made up of.