Locks and access
Master key systems and keying schedules: how they work
By the Div08 Consulting team · Updated
A master key system lets different keys open different sets of locks: each door has its own change key, a master key opens a group of doors, and a grand master key opens every group. The keying schedule is the document that assigns each door to a key, and it should be settled with the owner in a keying meeting before cylinders are ordered.
The levels of a master key system
| Key level | What it opens | Typical holder |
|---|---|---|
| Great grand master | Every lock in a very large system with several grand master groups | Owner or security director |
| Grand master | Every lock under its master key groups | Facilities manager |
| Master | A group of locks, such as one floor, department or trade | Department head, maintenance trade |
| Change key | One lock or one set of identical locks | Room occupant |
Most projects use two or three levels. More levels add flexibility but reduce the number of distinct change keys the system can produce and make it easier to compromise.
Keying schedules usually label keys with letter and number symbols that show the hierarchy, for example change keys numbered under the master they belong to. Use one consistent symbol style across the project and define it in the schedule legend.
Cross keying and why to avoid it
Cross keying means a lock is set to accept a change key from outside its own group, for example a supply closet that every office key opens. It is sometimes necessary, but each cross keyed cylinder adds key combinations to that lock, which makes the system less secure and can create unintended keys that open doors they should not.
Spec tip
when an owner asks for a lot of cross keying, it usually means the master key groups are drawn wrong. Regroup the doors before adding cross keys.
Cylinders, cores and keyways
- Conventional cylinders are rekeyed by a locksmith who removes and repins them.
- Interchangeable cores (IC), available in small format and large format, let the owner pull a core with a control key and swap it in seconds. Large owners with frequent changes often standardize on IC.
- Construction cores or construction keying let the contractor use the doors during construction, then the permanent cores or keying go in at turnover so construction keys stop working.
- Restricted or patented keyways limit who can cut keys, usually through a dealer agreement and an authorized signature list. They matter most at the grand master level, where an unauthorized copy is a building-wide problem.
Every cylinder type has to match the lock: mortise locks, cylindrical locks, exit device trim and padlocks may each need a different cylinder or core housing. See mortise vs cylindrical locks.
Running the keying meeting
The keying meeting is where the owner decides who gets into what. Have the floor plans, the door schedule and the hardware sets in hand. Cover:
- Who holds the grand master and master keys, and how many of each.
- Which doors share a change key (keyed alike) and which are unique.
- Existing system: is the project extending a building's current system, or starting a new one?
- Keyway: standard, restricted or patented, and who is authorized to order keys.
- Construction keying, and when permanent cores go in.
- Key delivery: how keys are tagged and shipped, usually directly to the owner, not the contractor.
Spec tip
get the owner's sign-off on the keying schedule in writing. Cylinders are factory combinated and rarely returnable, so a late change after ordering costs time and money.
What goes in a keying schedule
A usable keying schedule lists every keyed opening with its door number, room name, lock function, cylinder type, key symbol, and quantity of keys per symbol, plus the master and grand master key counts. It should reconcile one to one with the hardware sets, so every lock that takes a cylinder has a key symbol and every key symbol is on at least one door.
We build keying schedules as part of our hardware schedule service, checked against the lock functions in each set.
Frequently asked questions
What is a master key system?
A system of locks and keys where change keys open individual doors, master keys open groups of doors, and a grand master key opens everything in the system.
What is a keying schedule?
The document that assigns a key symbol to every keyed door and lists how many of each key are cut. It is approved by the owner before cylinders are ordered.
Is cross keying bad?
It is not forbidden, but every cross keyed lock reduces the security of the system. Use it sparingly and regroup doors first when possible.
What is an interchangeable core?
A lock core that can be removed with a special control key and replaced in seconds, so an owner can rekey a door without a locksmith or new hardware.
General guidance only. Code requirements depend on the edition your jurisdiction has adopted and on the listing of each fire-rated assembly; confirm with the authority having jurisdiction. Published by Div08 Consulting (John Voll, owner).