Construction Keying: Temporary Keys for Buildings Under Construction

The Basic Idea

Manufacturers use several mechanisms, but they share one pattern:

1. During construction, a construction key (sometimes called a construction master key or project key) operates the cylinders.
2. At turnover, a step is taken at each lock: a permanent key is turned, a part is removed, or a core is swapped.
3. Afterward, the construction key no longer operates the lock, and the permanent master and change keys take over.

The key system itself is designed in advance. BHMA's recommended practice for mechanical keying systems, ANSI/BHMA A156.28, is written for "building owners, security professionals and others responsible for designing, implementing, and maintaining secure keying systems." It also provides "guidelines for the essential keying conference," the meeting where a system is planned. The public summary does not say what A156.28 recommends for construction keying specifically.

Lost-Ball and Construction-Pin Systems

In conventional cylinders, the most common approach adds an extra part to one pin chamber. Falcon's support article explains its version:

• Falcon "utilizes a construction pin positioned in the third chamber of the cylinder." Other manufacturers "may use one or more ball bearings to create the lost ball mechanism instead."
• With the construction pin in place, the construction key can create a shear line and operate the lock.
• When construction is done, the system is deactivated by turning a permanent key. The construction pin then drops into a pre-drilled hole in the plug. After that, the construction key "can no longer create the necessary shear line to rotate the plug."

Falcon's catalog describes the same thing for its construction master keying: cylinders are "prepared with a special construction pin at the factory," and turning the top master key moves that pin "into a pocket of the cylinder plug, thereby eliminating subsequent operation" of the construction master key.

Because the first turn of a permanent key ends construction access, the order of events matters. Falcon notes that the deactivating key is the highest-level permanent key for that cylinder: the master key if there is one, otherwise the change key. It warns that "change keys and Master keys must not be utilized during the construction phase as they might deactivate the construction keying." Falcon offers this lost-ball keying on conventional, non-interchangeable-core cylinders only.

For background on how pin chambers, master pins and shear lines work, see pin tumbler locks and master keying. This article does not describe how keys are derived for any system.

Key-Block Systems

A second approach blocks the keyway instead of changing the pins. Falcon's Blockokey system ships locks with a plastic "key block" in the back of each cylinder's keyway. A shorter four-pin "Project Key" operates all cylinders during construction. At completion, a special extractor key removes the block from each cylinder, "thereby voiding operation of the project key."

Construction Cores

Buildings that use interchangeable cores can simply swap the cores. Schlage's glossary defines construction cores as "temporary cores for use during the construction phase of a building that can later be easily removed and replaced with permanent cores." Falcon's catalog says its temporary cores are keyed alike "to a combination unrelated to the permanent system's master key." When the building is handed over, the permanent cores go in and the construction cores are "returned to Falcon Lock for credit." Schlage lists both keyed and disposable construction cores.

Not every product supports every method. Schlage's key systems guide states that "construction master keying is not available for Primus XP cylinders," but construction cores can be supplied for interchangeable-core jobs.

Security Tradeoffs

Manufacturers themselves describe limits:

• Falcon on SKD locks. Falcon cautions that construction master keying of SKD sets "significantly limits the system's expansion and decreases the security of the SKD locks." Where it is needed, Falcon recommends issuing those locks "on a different keyway with their own (separate)" construction master key.
• Turnover is not automatic. Whether construction access has been fully cut off depends on the turnover step being done at every lock. Owners concerned about who held keys during the build can review key control and rekeying.

Related Topics

• Master keying
• Interchangeable cores
• Pin tumbler locks
• Key control
• Rekeying locks
• Restricted keyways

Sources