How to install a prehung interior door yourself: step by step
Shims, plumb on the hinge side, 1/8" gap. The whole job is one idea: get the hinge jamb dead plumb and perfectly straight, and the rest follows.
Difficulty 3 of 5 · about half a day · careful
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Photo of your room, the look you pick, then this guide with the materials counted for your room.
What you need
- Prehung interior door unit (correct width, height, jamb width, and hand)
- Composite or cedar shims
- 2-1/2" to 3" screws (to reach the framing through the hinge)
- 2" finish or brad nails for the nailer
- Low-expansion door and window foam
- Passage or privacy lockset
Tools
- 6 ft level (the single most important tool here) — A 4 ft level plus a straight board works if you cannot get a 6 ft one.
- Drill/driver
- Hammer and nail set
- Utility knife (trim shims flush)
- Wood chisel (only if you have to adjust a hinge mortise)
- Finish nailer (15/16 ga) with compressor, or cordless — $35–55/day in LA. You will want it again for casing and baseboards — rent for the whole trim weekend.
- Pry bar and a block of wood (removing the old jamb)
Step by step
Step 1 of 16
Confirm the opening and the unit match
Put your opening notes next to the box: width, height, jamb width, hand. Unwrap one unit and check it is not damaged or twisted before you start anything.
Step 2 of 16
Leave the shipping braces on the door
The factory blocks or staples that hold the door closed inside the jamb keep the frame in shape while you set it. Leave them until the jamb is fastened.
Step 3 of 16
Clean out the opening and check the floor again
No nails, no drywall lumps on the stud faces. Re-check the floor across the opening with a level and note the low side; you will shim the jamb leg on that side.
Ready to set the door?
- Finished floor is down in the room
- Opening is stripped to framing, clean and flat
- Door unit width, height, jamb width, and hand all match your notes
- You have shims, a 6 ft level, and a nailer or screws on hand
- You know which side of the floor is low
Step 4 of 16
Dry-fit the unit in the opening
Slide it in from the side the door swings toward. You want roughly 1/2" of play between the jamb and the framing all around — that is your shimming room. If it will not go in without force, the opening is too small; do not trim the framing yourself.
Step 5 of 16
Set the jamb flush with the finished wall
The face of the jamb should sit flush with the drywall on both sides, so the casing lies flat. If the wall is thicker, add a jamb extension rather than letting the casing rock.
Step 6 of 16
Plumb the hinge jamb first — both directions
Hold the 6 ft level on the face of the hinge leg and plumb it, then on the edge of the same leg and plumb it again. Both readings matter: face plumb keeps the door from swinging on its own, edge plumb keeps it from rubbing the stop.
Step 7 of 16
Shim behind every hinge
Slide a pair of shims (two tapered shims pointing opposite ways) in from both sides directly behind each hinge, plus one pair near the top and one near the bottom. Tap them until the level still reads plumb and the level shows no bow along the leg.
Step 8 of 16
Fasten the hinge jamb, and send one long screw into the stud
Nail or screw through the jamb and through each shim pair. Then remove one factory screw from the top hinge and replace it with a 2-1/2" to 3" screw that reaches the framing — that screw is what keeps the door from sagging. Snug only: stop the moment the reveal changes.
Step 9 of 16
Set the head jamb level
Check the head jamb with the level. If the floor was low on one side, the head comes level by shimming the short leg up off the floor; cut the opposite leg only if you have to, and never so the door drags.
Step 10 of 16
Work the latch side to a 1/8" reveal
Close the door. Shim the latch jamb behind the strike location and near the top and bottom until the gap between door and jamb is about 1/8" (3 mm) and the same from top to bottom, and the head gap matches. A nickel is roughly the right thickness to use as a feeler.
Step 11 of 16
Check the frame for wind (twist)
Close the door and look at where the door face meets the stop, top and bottom, on both legs. If it touches at the top on one side and at the bottom on the other, the frame is twisted: push the high leg in or out at the top and re-shim before you nail it off.
Step 12 of 16
The swing test
Take off the shipping braces. Open the door to a quarter, half, and three-quarters and let go each time. It should stay exactly where you left it. Drifting open or shut means the hinge jamb is not plumb — go back to the shims, not the hinges.
Step 13 of 16
Nail off the rest of the jamb, then trim the shims
Fasten through every remaining shim pair, then score the shims with a utility knife and snap them flush with the wall. If you use foam, use only low-expansion door and window foam in small beads and let it cure per the label before touching anything.
Step 14 of 16
Install the lockset and adjust the strike
Fit the latch and the lever per the instructions, then close the door. If the latch does not drop in cleanly, loosen the strike plate and move it a hair, or file the opening slightly — do not fix a latch problem by re-shimming a door that is already plumb.
Step 15 of 16
Check the bottom gap
You want a small, even gap over the finished floor — enough that the door clears carpet, rugs, and the threshold, usually somewhere around 1/2" to 3/4" over the floor for air return. Nothing should drag.
Step 16 of 16
Quality check before casing
Everything you do not fix now gets covered by the casing tomorrow. Run the list.
Quality check
- Hinge jamb is plumb on the face and on the edge
- Shim pairs behind every hinge, and one long screw into the framing
- Reveal is about 1/8" and even across the top and both sides
- Door stays put at any position — no self-swinging
- Door face meets the stop evenly: no twist
- Latch drops in smoothly and the door does not rub
- Shims trimmed flush; jamb faces flush with the wall
Common mistakes
- Setting the latch side first, or eyeballing plumb. The hinge jamb carries the whole weight of the door and controls everything. Get it plumb in both directions and dead straight, fasten it, and only then work the latch side to match. If you start anywhere else, the reveal will never come out even. Mistake #1 in this task.
- Shims anywhere but behind the hinges. A shim pair belongs directly behind every hinge. That is where the load is; without them the jamb flexes, the door sags, and the top corner starts to rub within a month.
- Driving screws until the jamb bows. Snug, not tight. Over-driven screws suck the jamb toward the stud between shims and put a curve in the hinge side. Check the reveal after every screw and back off if it changes.
- Regular expanding foam around the jamb. It keeps growing after it looks done and bows the jamb inward, so the door binds. Use only low-expansion door and window foam, in small beads, and leave the shims and the braces in until it cures per the label.
- A jamb in wind (twisted). Each jamb leg can be plumb and the frame can still be twisted, so the door touches the stop at the top on one side and at the bottom on the other. Close the door and look at the gap along the stop before you nail everything off.
- Uneven gap between door and jamb. The gap (the reveal) should be about 1/8" and the same all the way around the top and both sides. If it tapers, a shim needs adjusting — fix it now, because casing hides the problem, not the cause.
- A door that swings itself open or shut. That means the hinge jamb leans. Open the door to a few different positions and let go: it should stay put. If it drifts, the hinge side is not plumb.
Draft guide written from standard practice, not yet reviewed by a licensed pro. Follow product labels where they differ.
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