Everything You Need to Know About Door Jambs

Door styles may have changed but the purpose remains the same – separate one area from another. To know anything about doors, one must first understand the specific parts of the frame.

door jambs

In current building practice, one of the key components that ensure a door opens and shuts properly is the door jamb. The first recorded use of the word door jamb can be traced back to 1727, predating American independence by nearly 50 years. We may modify and improve the system, but key concepts that work will forever be useful.

What are Door Jambs?

Door jambs are the sides of the frame. The hinges are attached to one of the jambs depending on how you want the door to hang. On the other side, is metal plate bolted to the jamb to protect it from friction. In the middle of this plate is a hole that must be indented to fit the latch when the door is shut.

Door jambs are usually installed by cutting two identical pieces of the door frame, leaving room for the thickness of the header that’ll be placed above. Also be sure to measure the jamb width correctly, accounting for any drywall or siding that may be placed on the outer portion.

Jambs that are too small leave exposed wood, and those that are too large make for a difficult trimming job. Door frames are commonly framed using 2×4 or 2×6 studs.  For reference, a common jamb size for a 2×4 frame with drywall is around 4 and a half inches.

The lower portion of the jamb will sit directly on the floor. Consider using a plywood spacer to account for clearance issues. New wood or thicker carpet styles can create a situation where the doors won’t open and close properly.

Avoid cutting down your new door or living with a door that causes a hassle. A little extra space is better than none at all.

Once assured that the jambs are properly measured, nail them to the existing door frame. Make sure to use at least a 4’ level to make sure they’re square to account for variation throughout the height – uniformity is key.

In cases where the existing wall itself isn’t level, shims can assist in assuring that they’re level. If it can’t be obtained through this method, nudge the wall with a scrap block to project the wall and simply tap until it’s level.

Casing The Door/ Jambs

Casing is the process of applying trim to the areas around the frame of a door. Some methods of installation eliminate the need for this step, but when applicable this is a crucial step in assuring the appeal of the door.

When planning method of placing trim, reveal lines help creates a reference point for how much show will be necessary. A miter saw will see used to cut angles of corners of the trim to attach to the jamb, ensuring a tight hit.

Once angles and fit are checked, the trim will be tacked on to the jamb, following the reference point of the reveal lines. For added durability nails must be added, predrilling holes are recommended, this will ensure the wood will not be split and it also will produce a cleaner look.


The door jambs are one of the most important components of a door – it’s how the door is secured, what makes sure it stops, it bears the mass of the door through the hinges and is crucial in making sure the door looks and functions properly.

Now that you know the purpose of jambs, average widths, how to install as well as the type of jambs, the concept of doors should sound much more simple. Take a look at the doors around your home, identify the jamb, the type is visible.

View any open doorways in your home and strategize how a door would need to be installed to fill its position. If you decide to go about pursuing a new door project, make sure to follow the tips provided in this article to guarantee a successful door installation.

Feldco has been providing the Midwest with high quality exterior doors for over 40 years. All of our doors are installed by factory trained and certified professionals. Get a free quote now and join over 400,000 happy homeowners who trusted Feldco.

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