Interior Door Installation: Tools and Technique
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Hanging an interior door is one of those tasks that looks like it should be simple but has a few steps where precision matters. A prehung door (frame and all) is the easier path. Hanging a slab door in an existing frame requires more fitting and mortise work. Either way, the result should be a door that swings freely, latches cleanly, and has even gaps all around.
Prehung vs. Slab: Know What You're Working With
A prehung door comes already mounted in its frame with hinges installed. You remove the old frame and install the new unit as a complete assembly. This is the standard approach for new construction and most remodels. The advantage is that the door is already fitted to its frame — you just need to plumb and shim the frame in the rough opening.
A slab door is just the door, with no frame or hinges. Use a slab when the existing frame is in good condition and you're just replacing the door itself. You'll need to transfer hinge and latch locations from the old door (or from the frame), mortise the hinges, drill for the knob, and fit the door to the frame. It's more work but costs less and doesn't disturb the existing casing and trim.
Tools for Prehung Installation
A level (4-foot or longer) is the most important tool. The frame must be plumb on both sides and level across the top for the door to operate correctly. Cedar or composite shims adjust the frame position in the rough opening. A cordless drill with a Phillips or square-drive bit drives the fastening screws through the shims into the framing.
A hammer and finish nails (or a brad nailer) attach the casing trim. A miter saw cuts the casing at 45-degree angles for the corner joints. A utility knife scores paint or caulk on the old casing before removal. A flat pry bar removes the old frame and casing without destroying the surrounding drywall. A reciprocating saw cuts through stubborn nails holding the old frame.
Tools for Slab Door Hanging
A router with a hinge mortising jig, or a sharp chisel and hammer, cuts the hinge mortises in the door edge. A hinge mortise template (jig) clamped to the door edge guides the router for consistent depth and clean edges. Chisels work fine too — mark the hinge outline with a utility knife, chisel the perimeter cuts, then pare out the waste to the depth of the hinge leaf.
A hole saw (2-1/8 inch for standard knobs) and a 1-inch spade bit drill the bore and latch holes. A doorknob installation jig clamps to the door edge and guides both holes to the correct depth and alignment. Without the jig, you need to mark carefully and drill from both sides of the door to prevent blowout on the exit side. A block plane shaves the door edges for final fitting if the door is slightly oversized for the frame.
Fitting and Adjustment
The gap between the door and the frame should be about 1/8 inch on the sides and top (roughly the thickness of a nickel). The bottom gap depends on the flooring — 1/2 to 3/4 inch for carpet, 3/8 inch for hard floors. If the door needs trimming, mark the cut line with a straightedge and pencil, score the line with a utility knife to prevent tearout, and cut with a circular saw guided by a clamped straightedge.
If the door binds (rubs against the frame), check plumb on the hinge side. A frame that leans away from the hinge side at the top causes the door to bind at the top of the latch side. Adjusting the shims behind the hinges corrects this. Deepening one hinge mortise slightly (recessing the hinge further into the door or frame) pulls the door toward that hinge and can fix minor binding without reshimming the entire frame.
Latch and Strike Plate
Install the latch mechanism in the edge bore, the knob through the face bore, and test the operation before installing the strike plate. Close the door and mark where the latch contacts the frame. Mortise the strike plate at that location — a sharp chisel and a utility knife handle this in a few minutes. The latch should engage the strike plate smoothly without having to push or lift the door.
If the latch doesn't align with the strike plate, check whether the door has settled or shifted. A slight misalignment (less than 1/8 inch) can be corrected by filing the strike plate opening with a metal file. Larger misalignment means the door or frame has moved and needs correction at the hinges or shims. Self-adjusting strike plates with a spring-loaded ramp accommodate minor seasonal movement.
Frequently Asked Questions
How long does it take to install an interior door?
A prehung door takes about 1 to 2 hours to install for someone who has done it before, or 3 to 4 hours for a first-timer. That includes removing the old door and frame, installing the new unit, shimming, fastening, and attaching casing trim. A slab door replacement takes 2 to 3 hours because of the hinge mortising and fitting work. Budget extra time for the first one. After that, the process becomes routine.
Can I install a door by myself?
A prehung door is awkward to handle solo because the frame and door together are heavy and floppy. A helper holding the unit in position while you shim makes the job much easier. A slab door is lighter and can be handled solo. The trick for solo prehung installation is to screw a temporary cleat to the floor on the hinge side to hold the frame while you work on the latch side.
My door sticks in summer. Is that normal?
Yes. Wood doors expand with humidity and shrink when it's dry. Minor seasonal sticking is normal and doesn't require fixing unless it prevents the door from latching. If the sticking is consistent and annoying, wait until the humid season and plane the binding edge — the high spot will be shiny where it rubs. A light pass with a block plane fixes it. Don't overdo it, or you'll have a drafty gap in winter.