How to Replace a Door: Slab and Prehung Door Installation

Test the door by working it back and forth. You should have about 1/8-inch clearance at the header and strike sides and 1/16-inch clearance along the hinge side. Remove the door to make any adjustments.

Test the door to make sure it fits and swings freely.

Have a helper support the existing door. Using a screwdriver and hammer, tap the hinge pins up and out of the hinges. Take the door out of the frame. Uninstall the hinges and strike plates from the frame.

Pry the side jambs from the trimmer studs or trimmers — the vertical boards in the rough opening that support the header — and head jam from the header. You should now have just a rough opening in the doorway. Make any necessary repairs to the wall.

Use a level and carpenter square to make sure the rough opening is square, level and plumb. If the rough opening is out of square, you can use shims to make small adjustments for the new frame . Your prehung door installation information indicates how close to square, level and plumb the opening needs to be to work with your specific door. For example, a door might work with a rough opening that’s within 1/4 of an inch of square and 1/8 of an inch of level and plumb. Make sure the rough opening matches any other requirements for installation.

If you need to size the new door, measure the width across the opening at the top, bottom and middle. Measure the height at the left, center and right of the rough opening. Use the smallest of each of these sets of measurements to size your new prehung door. New prehung doors should indicate the acceptable rough opening sizes. Make sure your new prehung door is compatible with the rough opening.

Position the new door and door frame centered in the rough opening. Align the frame edge flush with the wall surface. Trim the side jambs as necessary to fit the door squarely in the rough opening. Allow space for the door to clear your flooring and ensure the gap under the door allows airflow per local codes.

Make sure the hinge-side jamb of the new frame is level and plumb. Insert shims between the jamb and trimmer if necessary, according to your prehung door installation instructions. Once the jamb is level and plumb, drive nails into the trimmer through the stop, jamb and each shim to temporarily secure the hinge side of the jamb. Shim and level the latch-side jamb and temporarily secure it with nails. Shim the center of the top jamb and secure with a nail. The frame should now be square. The door should operate easily and the space between the door edge and the frame should be equal around the frame. Adjust if necessary and resecure the frame.

Drive nails into the trimmers and header through stops, jambs and shims every 12 to 16 inches to permanently secure the frame. Use a nail set punch to set the nail heads below the surface of the frame. Fill the nail holes with spackling.

Trim off the excess shims. Install the casing around the door frame. Complete any necessary wall repairs and painting. Paint or stain the new door and frame as necessary. Once dry, install the doorknob, lever or lockset.