How to install an unassebled door and jamb in a door opening.
For most home owners installing a pre-hung is the best solution for many door replacement projects, but there are instances when an unassembled door is a better option. Unassembled doors, also called “knock-down” or KD doors, cost less than pre-hung doors and are easier to handle. There are also more options available with unassembled doors as you can special order the wood for the jamb and the door to match the design of your home. Unassembled doors can come with the latch and hinges mortised, or they can be entirely blank to allow you to match the hinge placement of existing doors. You need some decent carpentry skills to come out with a finished project that looks good and will last for years.
Other factors may lead you to purchase an unassembled door such as the door height, flooring material, wall thickness, and the style of the door slab and jamb.
Typical Door Framing
Tools and Materials
Flat pry bar
Finish nails, 4d and 8d
1. Check the 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 shims 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.
2. Shim the Trimmers
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.
3. Check the Door in the opening
Measure the distance between the shims. This distance should be between ¼ and ½ -inch larger than the width of the door and the two jambs.
4. Assemble the Door Jamb
Your KD door jambs should be routed at the top to allow the top jamb to slide in between. Typically the top jamb is cut to length for the door you are installing, but confirm this measurement by dry-fitting the pieces together and confirming the width of the assembled jamb.
Apply a bead of wood glue into the dado at the top of each jamb and slip the head jamb into place. Drill pilot holes through the backside of the jamb into the head and secure it with 8d finish nails or 2-inch drywall screws. Make sure that the edge of the head and side jambs are even.
Check the length of the jamb legs and cut them to length.
5. Anchor the jamb
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.
Tip: To adjust the height of the jamb, place a flat pry bar under the leg and slowly lever the jamb up until the head jamb is level.
6. Replace hinge screw and hang the door
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.
Screw the other hinge leaves into the door slab and hang the door in the jamb with the hinge pins.
Tip: Most doors have a slight bevel on the latch side, the place where the hole is drilled for the lockset. The door should close so that the short side of the bevel is closest to the door stop.
7. Install the door stop molding
The door stop is a narrow strip of wood that holds the door flush with the edge of the door jamb. Close the door so that the front edge of the door is flush with the edge of the jamb. Have someone help you to mark the location of the inside edge of the door while it is closed or measure the width of the door and mark the side and head jambs. Cut and nail the door stop into place using 4d finish nails.
Note: Some jambs will have matching door stop molding that fits into a groove in the jamb.
Tip: Set your combination square to the width of the door and transfer this distance onto the jambs.
8. 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.