When it comes time to install doors in your new home or remodel project, you can save a lot of time, labor and frustration by purchasing your doors as pre-hung units.

A pre-hung door is simply a door that is already attached to the jambs, which removes all the hassles of having to mortise the hinges into the jamb and into the edge of the door. This ensures complete accuracy in how the door is set up, which in turn translates into a much easier installation process.

Virtually any type of door is available as a pre-hung unit, including doors made of wood, metal, and fiberglass. Many common sizes and styles can be found in stock in home centers, door shops, and larger lumber yards, and special sizes, styles, and materials can be special ordered, typically within just a few days.

To select an interior pre-hung door, all you need to know is the door size, the jamb size, and the swing. Although a door can be cut and then pre-hung in just about any size to accommodate odd openings, commonly available stock sizes range from 2 feet to 3 feet in width in 2-inch increments, and 6 feet 8 inches in height. These sizes refer to the door itself, without the frame.

Jamb size refers to the width of the jamb, which needs to be the same as the overall distance between the face of the wall on one side of the door, and the face of the wall on the other size. For interior doors, there are two common jamb widths, 4 9/16 inches and 6 9/16 inches. A 4 9/16 jamb fits a wall constructed with 2x4 studs and 1/2-inch drywall on each side – 3 1/2 inches for the 2x4, 1 inch for the two drywall layers, and 1/16 inch of play. A 6 9/16 jamb is for walls with 2x6 studs.

Swing refers to which way a door swings open, and can be the subject of lots of confusion. However, determining a door's swing is actually quite easy. Stand in front of the door, so that the door is swinging open away from you. If the hinges are on your left, it's a left-hand swinging door; on the right, it's a right-hand door.

 

To install a pre-hung door you need a 2-foot level, a 4- or 6-foot level, wooden shims (available wherever you buy the door), and finish nails.

Prehung doors are shipped fully assembled, with the door and all the hinges mounted to the jamb. To keep the door from moving, it is typically secured to the jambs either with a couple of small nails driven through the jamb into the edge of the door, or with a disposable plastic lock that screws through the doorknob opening. Remove the nails or the plastic lock, remove the pins from the hinges, remove the door from the frame, and set the frame into the opening.

You will notice that the width of the opening is greater than the width of the door unit. That creates a space between the back of the jambs and the face of the studs, which allows you to insert shims as needed to get the side jambs plumb and the top jamb level.

Installation begins by getting the jamb on the hinge side plumb and set at the proper height. First, set your short level on the face of the top jamb. If the top jamb is level, or if it is low on the knob side of the door, no shimming is needed at the moment. If the top jamb is low on the hinge side, however, you will need to slip a shim between the floor and the bottom of the hinge-side jamb in order to level it.

Next, push the hinge-side jamb against the stud on that side, and then place your long level on the face of the jamb. Insert shims as needed to get the jamb plumb, then tack the frame in place with four finish nails – one on either side of the door stop up near the top of the jamb, and one on either side of the stop down near the bottom.

Reinstall the door on the hinges, and swing it closed. Add shims as needed to keep the jamb straight and plumb on the hinge side, and add a shim under the bottom of the knob-side jamb if necessary to level out the top jamb.

Next, start at the top of the knob-side jamb and add shims as needed to get an equal reveal between the jamb and the door edge all the way down. You will typically want to shim the jamb in at least four spots – near the top and bottom of the jamb, and a few inches above and below where the knob will be. Add more shims as needed to ensure the jamb is plumb and straight. Finally, complete the installation by adding finish nails in both side jambs as needed to secure the frame.