Commercial Master Key System Specification for Tenant Turnover

Why this matters

A commercial property's master key system is the security backbone of the property: every tenant lock, every common-area lock, every mechanical room, every roof hatch keys into a structured hierarchy that lets the property manager hold one Great Grand Master and individual tenants hold only the keys to their leased spaces. Tenant turnover (move-out, move-in, key returns, lost keys) routinely degrades the system. The contractor who designs the system properly at the outset and re-keys it cleanly at every turnover protects the property's security posture and earns recurring revenue. This article covers the specification work.

Hierarchy levels

A typical commercial master key system uses five levels:

• Great Grand Master (GGM): one key that operates every lock on the property.
• Grand Master (GM): operates a sub-group (e.g., a building within a campus, a floor within a high-rise).
• Master (M): operates a tenant suite plus the common-area locks for that tenant's floor or zone.
• Sub-Master (SM): operates individual zones within a large tenant suite (e.g., a tenant's executive area separate from the open office).
• Change Key (CK): operates a single lock.

Levels are conceptual; the cylinder design implements them via pin combinations.

Cylinder selection

Cylinder selection drives system longevity:

• 5-pin cylinders provide adequate combinations for small systems (under 50 locks). 6-pin cylinders are the commercial standard.
• 7-pin cylinders extend combination depth on large systems and on systems where bitting depth is constrained.
• Interchangeable core (IC) cylinders (Best, Falcon, Arrow, Medeco, Schlage Primus) allow the property manager to re-key by swapping cores rather than disassembling locks. IC is the preferred commercial standard because turnover rekeying is faster.
• Restricted keyways (Medeco, Mul-T-Lock, Assa, Schlage Everest 29, Sargent Signature, Corbin Russwin Pyramid) prevent unauthorized key duplication at the hardware store. The key blanks are controlled by the manufacturer or the locksmith dealer.
• High-security cylinders meeting BHMA/ANSI A156.30 Grade 1 (UL 437 listing) provide pick, drill, and bump resistance for high-value spaces.

For a commercial property, restricted keyway plus IC cylinder is the modern standard. The restricted keyway prevents tenants from duplicating keys at a kiosk; the IC core allows fast turnover rekeying.

System design constraints

The system designer balances:

• Total lock count and projected growth (build in 30 to 50 percent spare combinations for future additions).
• Number of master levels (more levels equal more keys but constrain combinations).
• Bitting depth (each manufacturer publishes the depth range and the MACS, Maximum Adjacent Cut Specification).
• Cross-keying (a single lock operated by multiple change keys; useful for shared conference rooms but reduces system combinations sharply).
• Selective key (a key that operates a subset of locks; useful for vendor access).

A small property (under 25 locks) is bit out on a piece of paper or a simple spreadsheet. A property of 100 locks or more uses master-keying software (Instacode, GMS Keyit, or the cylinder manufacturer's proprietary system).

Tenant turnover protocol

Standard turnover protocol:

• Move-out inspection: the property manager confirms key return count against the tenant lease records. Missing keys trigger rekey.
• Rekey decision: the property manager decides whether to rekey based on missing-key risk and lease language. Many leases require rekey at move-out at tenant's expense; some properties rekey on every turnover regardless.
• Cylinder pulling: pull the change-key cylinder for each lock on the rekey scope. With IC cores, swap the core to a previously bitted spare.
• Repinning: at the locksmith's bench, repin the cylinder or core to a new change-key combination. Verify operation across the master hierarchy on a test key board.
• Reinstallation: reinstall the cylinder, verify operation with the change key and with the master key.
• Key cutting and distribution: cut new change keys to the new combination; deliver to the property manager with a signed receipt; void the prior combination in the master-keying records.

Records and key control

The master-keying records are the property's security IP and the contractor's deliverable:

• Combination chart: which cut combination is assigned to which lock, change key, master key, and so on up the hierarchy. Treat as restricted; store encrypted.
• Key inventory: every cut key, its bitting, its assigned holder, the date issued, the date returned.
• Lock inventory: every lock, its location, its cylinder type, its current combination, its rekey history.
• Key-control authorization list: who is authorized to request keys from the locksmith. The contractor should refuse key cutting requests that come from outside the authorized list.

These records are confidential. A locksmith who hands over the combination chart in response to a phone call from "the new property manager" has compromised the property. Verify identity through a known channel before releasing records.

BHMA / ANSI A156 grade selection

• BHMA Grade 1: heavy-duty commercial (high-traffic doors, security-critical doors). The standard for commercial buildings.
• BHMA Grade 2: medium-duty commercial (interior office doors, lower-traffic spaces).
• BHMA Grade 3: residential and light commercial; rarely appropriate on commercial property.

Spec Grade 1 on exterior, mechanical rooms, IT closets, and tenant suite entries. Grade 2 may be appropriate on tenant interior doors when budget dictates; document the spec deviation.

References

• BHMA / ANSI A156.5 Auxiliary Locks and Associated Products.
• BHMA / ANSI A156.13 Mortise Locks and Latches.
• BHMA / ANSI A156.30 High Security Cylinders.
• UL 437 Key Locks (high-security cylinder listing standard).
• ALOA Master Keying Theory and Practice, current edition.