Keying and Master Key Systems: How MDH Keeps Your Building Secure

Every building has doors. And every door that locks needs a key strategy.

For a small office with three employees, that might be simple. But for a school, a medical facility, a hotel, or a multi-story office building — keying becomes one of the most important and most underestimated parts of the project. Get it right from the start, and your building runs smoothly for years. Get it wrong, and you're re-keying locks, cutting duplicate keys, and fielding calls from frustrated facility managers.

At MDH, keying is something we take seriously — and something we help our contractors and building owners plan well before the first door is hung.

What Is a Master Key System?

A master key system is a structured hierarchy of keys that gives different people different levels of access throughout a building — without requiring a separate key for every single lock.

Here's a simple way to think about it:

A building engineer might carry one key that opens every door in the facility. A department manager might carry a key that opens every door in their wing. An individual employee carries a key that opens only their office and the common areas they need to access. Every lock in the building is keyed to fit within that hierarchy. One key, at the right level, opens exactly what it's supposed to — and nothing more.

This is the master key system. And when it's designed correctly, it's elegant. When it's designed incorrectly — or added onto piecemeal over the years — it becomes a security liability and a logistical headache.

The Levels of a Key System

Commercial key systems are typically organized into levels:

The change key is the lowest level — it opens one specific lock and nothing else. This is the key an individual employee or tenant carries.

The master key opens all locks within a defined group — a floor, a department, a wing. A supervisor or manager typically carries this level.

The grand master key opens all locks across multiple groups within a building. Facility directors and security personnel typically carry this level.

The great grand master key, used in larger or multi-building campuses, opens everything across all groups and structures. This is the top of the hierarchy — usually held by ownership or senior administration.

Designing this hierarchy correctly at the start of a project — before hardware is ordered — is critical. Changing it later means re-keying locks, ordering new cores, and in some cases replacing hardware entirely.

Why Early Planning Matters

One of the most valuable things MDH does on a commercial project is get involved in the keying conversation early.

When a contractor or building owner engages us at the beginning — during design or specification — we can help map out the access hierarchy for the building, specify the right key system and cylinder brand, coordinate with the hardware schedule, and ensure every opening is properly accounted for. We work with all major key system manufacturers to find the right fit for the building type and security requirements.

By the time doors are being installed, everything is already planned. The keys are cut, the cores are pinned, and the system works the way it was designed to from day one.

When keying is an afterthought — addressed after the hardware is already in — it creates mismatches, gaps in the access hierarchy, and often unnecessary expense.

Re-Keying and Ongoing Key Control

Master key systems don't only apply to new construction. MDH also handles re-keying for existing buildings — a service that's more common than people might expect.

Buildings change. Employees leave. Tenants turn over. Keys get lost. When any of these things happen, the security of an existing key system is compromised. Re-keying — replacing the internal pin configuration of a lock cylinder — restores that security without requiring new hardware.

MDH can assess an existing key system, identify where it's been compromised or outgrown, and re-key the building back to a clean, controlled hierarchy. In some cases, we recommend transitioning to a restricted keyway system — a higher-security option where key duplication is controlled and unauthorized copies can't be made at a hardware store.

High-Security Key Systems

For buildings where key control is especially critical — healthcare facilities, schools, government buildings, financial institutions — restricted keyway systems offer an additional layer of protection.

These systems use patented keyways that cannot be duplicated without authorization from the building owner or facility manager. Every key is tracked. Every copy requires documentation. It's a meaningful upgrade in security for buildings where access control truly matters.

MDH works with key system manufacturers that offer restricted keyway options across a range of security levels, and we can help specify the right system for your project requirements.

One Part of a Larger Opening

Keying doesn't exist in isolation. It's one component of a fully coordinated commercial opening — working alongside the lockset, the door, the frame, and in some cases, electronic access control systems. When MDH is involved from the beginning, all of those components are specified, coordinated, and installed to work together.

That's what being a value-added distributor means in practice. It's not just supplying hardware — it's making sure the whole opening works the way it's supposed to, for the life of the building.

Ready to talk through keying for your next project? Reach out to our team at www.midwestdoor.net/contact and let's get started.

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