Master Keying a Small Office Building

The system requires three levels: grand master (opens all), master (maintenance staff: all suites, maintenance closet, common doors), and change keys (tenant keys: individual suite + common doors). The common doors must be mastered to both the grand master and all tenant keys, so they will have pins mastered to the grand master and to each tenant change key? Actually, common doors need to be opened by all tenant keys, the maintenance key, and the grand master. That means the common door cylinders must be keyed to accept all tenant change keys, the maintenance key, and the grand master. This is typically done by making the common doors a separate master level? Wait: if all tenant keys must open the common doors, then the common door lock must be keyed so that each tenant key operates it. That implies the common door cylinder is mastered to all tenant change keys, which is a high-level master key itself. This is a security risk: any tenant key opens the common doors, which is intended, but it also means the common door cylinder must be pinned to accept many different keys. The proper approach is to make the common doors operated by a separate "common" key or by the tenant keys? The requirement says tenant key opens suite and common entry doors. So the common doors must be keyed to accept all tenant keys. That means the common door cylinder is a master key cylinder that has all tenant change keys as sub-masters? Actually, in master keying, a cylinder can be mastered to multiple keys by having multiple shear lines. For a 6-pin cylinder, you can have up to a certain number of shear lines per pin. But having 12 tenant keys plus maintenance plus grand master on one cylinder may exceed the practical number of shear lines. A better design is to use a separate "common door" key that is issued to all tenants, but the requirement says the tenant key itself must open the common doors. So we need to master the common doors to all tenant keys. This is feasible if we use a keying system where the common doors are at a higher level than the suites? Actually, if the common doors are at a higher level, then the tenant keys would not open them unless they are also mastered to that level. The typical solution is to make the common doors a separate master level that is included in all tenant keys? That would mean the tenant keys are actually sub-masters. But then they would open other suites? No, if the tenant key is a change key for the suite, it cannot also be a master key for the common doors unless the common doors are keyed to that change key. So each tenant key must be individually added to the common door cylinder. That means the common door cylinder will have 12 different shear lines for the tenant keys, plus the maintenance key and grand master. That is 14 shear lines, which is impractical for a 6-pin cylinder (max shear lines per pin is typically 2-3). Therefore, the requirement as stated is not feasible with standard 6-pin cylinders without using a separate key for common doors. A practical solution is to issue each tenant a suite key and a separate common door key, or to use an electronic access system for common doors. Alternatively, use a keying system with more pins or a different keyway that allows more shear lines. Since the problem states we have Schlage C 6-pin, we must explain the limitation and propose a workaround: use a separate common door key or rekey common doors to a master key that is issued to all tenants in addition to their suite key. The model answer should identify the conflict and propose a feasible design: e.g., make the common doors operated by the grand master and a separate "common" key that is issued to all tenants, or use a master key system where the common doors are at the grand master level and tenant keys are not expected to open them (contradicts requirement). So the correct judgment is to flag the infeasibility and recommend a two-key system or electronic access.

To allow expansion, reserve one or more pin positions for future mastering. For example, use a 6-pin cylinder but only use 5 pins for the current system, leaving the 6th pin as a constant or reserved for future levels. Or use a progressive master keying approach where the grand master uses a specific cut in a designated pin (e.g., pin 6) that is not used by any current change keys, allowing future change keys to be added without affecting existing keys. Also, ensure that the keying chart has unused shear lines in the common doors? But common doors are already problematic. For suites, each suite cylinder can be keyed with a unique change key that is mastered to the maintenance master and grand master. To add a new suite, you need to cut a new change key that fits the new cylinder and also operates the maintenance and grand master. This requires that the new change key's cuts are compatible with the existing master key cuts at the mastered pins. By planning the master key cuts to have multiple valid depths at certain pins (e.g., using a 2-step progression), you can accommodate additional change keys. The key is to document the system and leave room in the keying matrix.