One Lock Body, Three Different Jobs
This guide is for commercial installers, facility managers, and specifiers who need to assign the correct mortise lock function to openings that serve mixed-use corridors, multi-family entries, or public restrooms. Apartment function, exit function, and public toilet function mortise locksets often share the same Grade 1 case and trim footprint, but they behave in fundamentally different ways once the door is in service. Choosing the wrong one before the door is prepped creates a costly field correction and, in some buildings, a code problem.
What Is a Mortise Lock Function Code?
A mortise lock function code describes the operational behavior of the latch, deadbolt, and trim under all conditions: from the inside, from the outside, and in response to a key. The same physical case can be configured for dozens of functions. The three covered here are frequently grouped together in schedules because they appear on similar-looking openings, but each one serves a distinct security and life-safety purpose.
Apartment Function: Controlled Entry, Free Egress
Apartment function is designed for residential-style corridor doors in multi-family buildings, dormitories, and similar occupancies where the occupant needs to lock themselves in without a key but must always be able to exit freely.
- Outside: Key retracts the latch. Outside lever or knob is normally locked and requires a key to operate.
- Inside: Thumb turn controls the deadbolt. Inside lever always retracts the latch for free egress.
- Net result: The occupant can deadbolt from inside without a key; entry from the corridor always requires a key.
This function is appropriate for individual sleeping units, dormitory rooms, and apartment entry doors. It is not the right choice for any door that is part of a required means of egress serving an assembly or common corridor in an occupancy where panic hardware or a simpler free-egress function is mandated.
Exit Function: Free Egress on a Lockable Entry Door
Exit function mortise locksets are built for doors that must remain freely operable from the egress side at all times while allowing controlled entry from the outside. This is the workhorse function for stairwell corridor doors, back-of-house passages, and service entries in commercial buildings.
- Outside: Locked at all times; key retracts the latch for authorized entry.
- Inside: Lever always retracts the latch freely, with no thumb turn or auxiliary deadbolt to engage.
- Net result: Continuous free egress; entry is always key-controlled.
The critical distinction from apartment function is the absence of an inside thumb turn deadbolt. In an exit function opening, a building occupant cannot inadvertently or deliberately deadbolt themselves in a space that is on a required egress path. For stairwells and service corridors in commercial, healthcare, or educational buildings, this matters for both life safety and code compliance under NFPA 101 and the International Building Code.
When Exit Function Gets Confused With Storeroom Function
Exit function and storeroom function are sometimes conflated because both lock the outside lever. The difference: storeroom function does not allow the inside lever to retract the latch freely in all configurations. Always verify the function code against the door schedule before ordering. Using storeroom function on an exit-side door can create an egress violation.
Public Toilet Function: Occupied Indicator Without a Key
Public toilet function is purpose-built for single-occupancy restrooms in offices, retail environments, restaurants, healthcare facilities, and schools. The defining feature is the indicator: a visual signal (typically a colored flag or window on the trim or door face) that shows whether the space is vacant or occupied.
- Outside: Lever is free when unoccupied. When the interior thumb turn is engaged, the outside lever is locked and the indicator signals occupied.
- Inside: Thumb turn locks the outside lever and activates the indicator. Inside lever always allows free egress.
- Emergency access: Most public toilet function locksets include a coin-slot or small-blade release on the outside trim so staff can unlock the door from the corridor without a key in an emergency.
This function is distinct from a standard privacy function in that it is explicitly designed for high-traffic, accessible public restrooms where ADA compliance and emergency access are both requirements. Grade 1 hardware is the correct specification here; residential-grade privacy sets are not appropriate for commercial restroom doors with heavy daily use cycles.
ADA Considerations Across All Three Functions
All three function types are available with lever trim rather than knob trim, which is the minimum requirement for accessible hardware under ICC A117.1. Verify that the lever design meets the one-hand, no-tight-pinching-or-twisting standard and that the operating force on the latch does not exceed five pounds on an accessible route. The thumb turn on apartment and public toilet functions must also be operable without tight grasping. If the opening is on an accessible route, confirm ADA-compliant trim at the time of specification, not at punch list.
Fire-Rated Openings: Function Restrictions Apply
If any of these three openings carry a fire rating, the mortise lock must be listed for use on fire-rated assemblies. Not every function is available in a fire-rated configuration from every manufacturer. Confirm UL listing for the specific function and case before the door is prepped. Public toilet function with an indicator is sometimes a special-order item on fire-rated openings. Build lead time into the schedule accordingly.
Reading the Schedule Before the Door Is Prepped
The most common field problem with these three functions is a door that has already been prepped to the wrong prep standard because the function code was assigned late or incorrectly. Mortise lock cases require a precise pocket routed into the door stile. If the case changes, the prep changes. Establishing function codes at the hardware schedule stage, not at rough-in, prevents this problem.
- Confirm occupancy type and egress path before assigning apartment or exit function.
- Confirm restroom is single-occupancy before specifying public toilet function; multi-stall restrooms use a different hardware approach.
- Check fire rating early; some functions require special-order cases with longer lead times.
- Verify trim compatibility with the lock case; sectional trim and integral trim have different prep requirements.
Preferred Hardware for These Applications
For Grade 1 mortise locksets in apartment, exit, and public toilet functions, DoorwaysPlus stocks and sources from lines known for stable part availability and field-serviceable components, including Accentra (formerly Yale Security), Corbin Russwin, Sargent, and Hager. These lines maintain consistent case dimensions and trim families across product generations, which reduces the risk of compatibility problems when a component needs replacement years after initial installation. That kind of parts stability matters most in multi-family and institutional settings where dozens or hundreds of identical openings are in service simultaneously.
Contact the DoorwaysPlus team to confirm function codes against your door schedule, verify fire-rating requirements, and source the right Grade 1 mortise lockset for each opening type before the doors are prepped.