Double Cylinder Deadbolt Installation

How a Double Cylinder Deadbolt Works

A standard single cylinder deadbolt pairs a keyed pin tumbler cylinder on the outside with a simple thumbturn on the inside. A double cylinder deadbolt swaps that thumbturn for a second keyed cylinder, so the bolt only moves when someone turns a key - from either side. Both cylinders are normally keyed alike, so one key runs the whole lock.

The bolt itself works like any quality deadbolt: a solid metal bolt that should throw a full 1 inch into the strike pocket. Better models add hardened steel inserts and anti-saw pins in the bolt, plus drill-resistant plates guarding the cylinder pins.

When a Key on Both Sides Makes Sense

The classic reason to choose a double cylinder deadbolt is glass within arm's reach of the lock. If a pane can be broken and a hand reached through, a thumbturn hands an intruder an easy way in. A second keyed cylinder removes that shortcut. Common candidates include:

• Doors with sidelites - the narrow glass panels beside the frame
• Half-glass or full-glass back doors and French doors
• Doors with decorative glass inserts near lock height

It is not the only answer, though. Security film over the glass or a reinforced single cylinder setup can address the same risk without the safety trade-offs covered next.

Safety and Building Code Trade-Offs

The trade-off is serious and worth stating plainly: in a fire or other emergency, you need a key to get out. Building and fire codes treat required exit doors carefully, and many jurisdictions restrict or prohibit double cylinder deadbolts on a home's primary egress door. Rules differ from place to place, so check with your local building department before committing.

If you do install one, safe habits matter:

• Keep a key mounted near the door, out of sight and beyond reach of any glass
• Never lock the interior cylinder while people are inside without that key in place
• Ask about captive thumbturn cylinders, which let a key dock inside and turn like a thumbturn, then release when you leave

What a Careful Installation Involves

Fitting a double cylinder deadbolt follows the standard deadbolt layout with a few extra checks. The door needs a 2-1/8 inch cross bore and a 1-inch edge bore, drilled at a backset of 2-3/8 or 2-3/4 inches to match the hardware. Both cylinders must sit square so the tailpiece engages cleanly; a cocked cylinder makes the key drag on one side.

Strike alignment matters even more here - if the bolt cannot throw its full length into the strike pocket, the lock loses much of its strength. A proper install also adds a heavy-gauge strike plate anchored with 3-inch screws that reach the wall stud, and keys both cylinders alike, matched to your existing keyway if you want one house key. Hardware is graded under ANSI/BHMA standards from Grade 3 up to Grade 1, and the grade affects how the lock resists kicking, wrenching, and drilling.

If a double cylinder deadbolt sounds right for your glass-panel door, call (916) 913-5080, describe your door and lock setup, and confirm the service is a fit before any technician is scheduled.

Frequently Asked Questions

Are double cylinder deadbolts allowed on home exit doors?

It depends on local building and fire codes. Many codes restrict key-locked deadbolts on required egress doors because occupants must be able to exit quickly in an emergency, while some allow them on secondary doors or with conditions. Your local building department can tell you what applies to your door. If code rules it out, alternatives like security film on nearby glass or a reinforced single cylinder deadbolt can address the same break-and-reach risk.

Can one key work both cylinders and match my other locks?

Yes. Both cylinders in a double cylinder deadbolt are normally keyed alike from the factory, so a single key operates the inside and outside. A locksmith can also rekey both cylinders to match your existing house key, as long as the new deadbolt uses the same keyway as your current locks. If the keyways differ, choosing a deadbolt from your existing key family at purchase time solves it.

How do I stay fire-safe with a key on both sides?

Keep a spare key mounted close to the door but out of sight and beyond arm's reach of any glass, so everyone in the home can exit fast. Never lock the interior cylinder at night or while people are inside unless that key is in its spot. Captive thumbturn cylinders are another option: the key docks inside and turns like a thumbturn while you are home, then releases when you leave.

Call (916) 913-5080 about double cylinder deadbolt installation.