Add flair and protection to your home with a pre-hung door from Home Depot. This project should only take an hour, but make sure the door and frame are level and plumb before beginning!
Use a 4-foot level to inspect both hinge- and latch-side frames on a 4-foot level floor surface, and shim the jambs if necessary.
Measure the Door
Before installing the door, take several measurements to ensure it will fit as intended. Start by measuring the existing rough opening from jack stud to jack stud and from header to floor to ensure its width fits comfortably with your new door unit. Record any shorter measurements.
Use a pry bar to pry away the trim surrounding an existing door and expose its frame’s height and thickness. Measure height at two locations along each side of the frame in order to identify any variations in door panel size variances.
Measure the depth of the jambs (or frames), to ensure it complies with wall’s standard thickness (4 9/16″, 5 9/16″, and 6 9/16″) without siding or trim pieces. Shim the side jambs on one hinge side until level, before repeating this process on its partner latch side.
Cut the Jambs
Pre-hung doors may include side jambs that extend above the floor. If you want to avoid carpeting these areas later, cut these back.
To determine how much to reduce jamb height, place a level across the floor and note where it bubbles up. Use a jigsaw to cut away at high jamb sides of doorways.
Shim any jambs necessary to bring them up to floor level. A great way to achieve this is to rest a 4-foot level on the floor at the hinge side of a doorway and slip shims underneath until its bubble centers on the floor and its opposite side appears square with respect to walls.
Shim the Jambs
Goal of setting the door frame square in its opening. This requires making sure it is level and plumb while also being parallel with any adjacent walls or trim.
To check for plumb, use a 6ft level to inspect the jack stud (which supports the header) on the hinge side. Shim the frame as necessary until your level indicates plumbness.
Shimm the strike-side jamb if necessary to raise it, and secure a block of wood against the wall to hold the jamb in place while working. Consider replacing one factory screw at each hinge location with longer ones that can penetrate framing; this will prevent casing sagging. Shim away until you achieve an even reveal.
Install the Jambs
If the door jambs are thicker than their frame openings, use wood shims to raise them until they’re flush with the framing. In extreme cases, cutting down and raising side jambs might also be necessary in order to accommodate flooring or make room for casing.
Place a 6-ft level on the floor near your doorway to make sure the hinge stud on its side is level with a plumb line on your level. Shim this side until your level indicates it is, then secure all shims firmly into place with tape.
Attach temporary cleats to the wall as stops for your door frame, then use shims on one side of jambs to keep them tight against drywall. Hide any nail heads with putty.
Install the Door
Once the shims have been installed, temporarily secure the door unit with screws or staples until further inspection. Use a level to measure the height of your jambs; ensure the bottom of each door clears the floor by at least 1/2 in for optimal performance – otherwise additional trimming may be needed later on.
Measure your door for height and width using standard measurements: taking height measurements from the top of the rough opening sill to the edge of jamb on one side; width measurements should start on hinge side of jamb on opposite side.
Assuming you take accurate measurements, a pre-hung door should fit comfortably into its intended spot. If there are any issues, seek professional assistance; otherwise you can paint or finish the door to match its trim.