What is a Door Jamb?

Doors are pretty complicated pieces of machinery, comprising of multiple different parts which work together for seamless functioning. One of the vital parts of a door is the ‘door jamb’, often misspelled as ‘door jam’. 

Definition of a Door Jamb

Let’s start with a plain English definition of a door jamb: a door jamb is one of the posts which sit on either side of the door, forming the vertical portions of the door frame.

What’s the Difference Between a Door Jamb and Frame?

Simply put, the door jamb is a specific part of the frame. It’s there to take the weight of the door, as well as help keep the rest of the frame square and stable. Your hinges are affixed to the jamb on one side of the door, while the bolt passes through the jamb on the other side. The door frame is comprised of several parts, including the door jambs, sill and head. 

Door jambs aren’t just found on standard, single doors – they’re also part of sliding, folding, and double-doors, on which they serve much the same purpose.

The ‘plumbness’ of a jamb has a significant influence on the function of the door. If a door jamb is ‘plumb’ it means it’s perfectly vertical, the way that ‘level’ means something is perfectly horizontal. Just a few degrees outside of 90°, and you’ll find that your door rubs against the frame, or that the bolt doesn’t properly align. If the surrounding walls aren’t entirely plumb, you can correct this with the help of a few strategically-placed shims.

It’s also crucial that the jambs are of the same height, and not too tall or too narrow – if so, you might end up with excessive gaps (or no gaps at all).