How to Add a Lock to a Den Door

Remove the old den doorknob with a screwdriver by unfastening the plate screws. If your den's door does not have an existing knob, cut a hole with a drill and paddle bit that will accommodate the knob's circumference. Drill another hole in the wall on the door jamb for the latch.

Unfasten the old den door knob by pulling it apart, saddling both sides of the door and pulling from each side with your hands. Unscrew the latch plate and strike plates with a screwdriver to replace with the new doorknob set.

Insert the new doorknob with the lock switch facing the interior of the room. This step can be easily overlooked and will create additional work of disassembling the new knob only to reverse it. Feed the interior and exterior couplings into one another and push the latch through the side of the door.

Try the lock with the door still open to see whether the outside knob will not turn. Tighten the plate screws and twist the doorknob to see the latch protract and retract. Fasten the new den doorknob's latch and strike plate to the wall and side of the door using the screws in the packaging.