Older homes around Havertown, the Main Line and Philadelphia often still have their original front doors, and many of them are worth keeping. But a door built decades ago was not made for the lock you pick up at a hardware store today, and forcing one in is how a good door gets damaged.
Here is what to know before choosing a lock for an older door.
Why a modern lock doesn't always fit
Many older doors use a mortise lock: a rectangular lock body that sits in a deep pocket cut into the edge of the door, with the knob, the key and the latch all working through it. A typical modern deadbolt works differently and needs a round hole bored through the face of the door.
Older doors can also be thinner, have different distances from the edge to the lock, or have glass panels close to the handle. All of that changes what will fit.
Option 1: Keep the mortise lock and service it
Many old mortise locks are solidly built. If yours is working, cleaning it, repairing worn parts and rekeying the cylinder may be all it needs. You keep the original look and the door keeps its original shape.
Option 2: Replace it with a new mortise lock
If the old lock is worn beyond repair, a new mortise lock can often go into the existing pocket. It is the least invasive way to get a new lock on an old door.
Option 3: Add a separate deadbolt
On a door that is thick and solid enough, a separate deadbolt adds a second point of locking. Where it goes matters: too close to the existing lock pocket and it weakens the edge of the door. This is worth planning before any drilling happens.
Option 4: A rim lock on the inside face
A rim lock mounts on the inside surface of the door, with a small cylinder through the door. It needs far less cut out of the door than a bored deadbolt, which makes it a good fit for some older or thinner doors.
What to check before buying anything
- How thick the door is, and whether it is solid wood or a veneer over a lighter core.
- What is already cut into the door: the mortise pocket, old bore holes, filled holes.
- How far the lock sits from the edge of the door.
- Whether there is glass close enough to the lock to reach through.
- How the door fits the frame. A lock only works as well as the door closes.
An old door doesn't have to be a weak door
Much of a door's strength is in the strike plate on the frame and the screws that hold it. A reinforced strike with longer screws makes a big difference on an older frame, and it doesn't change the look of the door.
If there is glass within reach of the lock, mention it when you call so we can look at that door with it in mind. Whatever lock goes on, everyone inside should be able to open the door from the inside without hunting for a key, because that is the way out in an emergency.
