Check the rough opening Place a 4-foot level on the floor in the doorway. If the hinge side is lower than the latch side, slip shims under the level nearest the hinge jamb. Adjust the until the level's bubble is centered. Tack the shims to the floor with a finish nail. If the latch side is lower, no shims are needed. Check the walls and the trimmer studs for plumb using a level or plumb bob. Also, check the trimmers' faces with a framing square to see if they are square to the wall. Finally, check that the trimmers are parallel by measuring between them at the top, bottom, and middle of the opening. If the wall is out of plumb, or the trimmers are out of plumb, out of square, or not parallel. On the hinge jamb, measure from the bottom of the jamb to the center of each hinge. Mark the hinge locations on the hinge-side trimmer by measuring up from the floor (or top of the shims). Tack the plumb bob to the top of the hinge-side trimmer, and measure the gap between the string and the trimmer at each hinge location.
Where the gap is the smallest, place overlapping shims. Adjust the shims to 1/8 inch thick, and tack them with a finish nail. Measure the gap between the shims and the plumb bob string. Place overlapping pairs of shims at the other two hinge locations. Adjust each pair's thickness until the gap between shims and string equals the gap at the first pair. Nail each pair to the trimmer and cut off the ends with a utility knife so they don't protrude past the drywall. Fit door into opening Lift the door into the rough opening and push the hinge jamb tight against the shims tacked to the trimmers. Tack an 8d finish nail through the face of the hinge-side casing 3 inches below the miter, into the trimmer. Hold a level against the face of the casing and adjust the jamb in and out until plumb. If the wall is plumb and the casing rests flush against it, tack 8d finish nails through it at the other two hinge locations. If the wall is out of plumb and the casing does not rest against it, shim behind the casing at the hinge locations to make the door plumb.
Nail through the casing and shims and into the trimmer. Fill any gaps between the casing and the wall with tapered wood wedges. Check the horizontal gap, or "reveal," between the top of the door and the head jamb. It should be uniform from left to right and 1/8- to 3/16-inch wide. If necessary, adjust the reveal by pushing up the head casing. Set this reveal by driving an 8d nail through the face of the latch-side casing and into the trimmer, near the top of the door. Check the vertical reveal between door and jamb on the latch side. It should be about the thickness of a nickel. To adjust it, grab the casing and move the jamb by hand. Open and close the door to check that its leading edge, the one that rests against the stop, clears the jamb by a consistent 1/8 inch. Set the reveal by driving 8d finish nails every 16 inches through the latch-side casing and into the trimmer. Make sure the reveal remains consistent. Slip a pair of shims between main jamb on the latch side and the trimmer, near the top of the door opening.
When they are just touching the back of the jamb without putting any pressure on it, nail them to the trimmer with 8d finish nails. Nail additional pairs of shims a few inches above the base of this jamb, as well as just above and below the strike plate. Without these shims, the jamb could flex. On the hinge jamb, remove the center screw from the top hinge leaf and replace it with a screw that's long enough to penetrate the trimmer. This prevents the door from sagging and binding. Tip: If the long screws don't match the ones that came with the hinges, install them behind the hinge leaf. Attach the split jamb Starting at the bottom, gently push the edge of the split jamb into the groove in the main jamb. Tap the two jambs together using both hands. Nail the casing to the wall on both sides of each miter, and about every 18 inches along the casing. To hold the two jambs together, drive 8d finish nails through the stop and into the trimmers: one nail at each hinge location, one through the shims near the top and the bottom of the latch jamb, and one each just above and below the striker.
Do NOT nail into the head jamb. Mount the latch hardware Fasten the strike plate to the mortise in the latch jamb using the screws provided. If the plate is bigger than the mortise, put the plate on the jamb, outline it with a pencil, and chisel to the outline. Slip the latch bolt into its bore and fasten its plate into the mortise on the door's edge with the screws provided. If the mortise is too tight, adjust its size in the same way as you did the strike plate. Fit the knobs to both sides of the latch bolt, then insert and tighten the connecting screws that hold the knobs together. Close the door and listen for the latch sliding into its strike. If the door rattles, bend the prong on the strike plate slightly toward the stop. If the latch doesn't catch, bend the prong away from the stop. Tighten all the screws.When ordering a pre-hung door, you will have the choice of a right- or left-hand swing, as well as having the manufacturer drill the holes in the door for the locksets.
If the unit arrives with a brace to keep the door and frame aligned, leave the brace on until the door unit is plumbed, shimmed and secured into place. DK - Do It Yourself Home Improvement, 2009 Dorling Kindersley Limited Trim any excess drywall around the doorway to make sure the new door will hang plumb. Mark for any shims that are needed under the level. Measure and mark against the jamb where any shims are needed. Cut the door to the appropriate length. Remove the plug that comes on the pre-hung door, as well as the temporary trim on the bottom of the door. Tack one nail on a shim in the doorway to get started. Place the door inside the opening. Position the door so it is plumb, and the door is able to swing open. Secure the jamb with nails along its length. Use a straight edge to check the door opening, ensuring that it has room to open and close (Image 1). With the door closed, place a shim by the bottom hinge to accommodate any adjustments (Image 2).