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The correct way to hang an interior door depends on what you bought. A prehung door arrives as a slab already attached to its frame, so you fit the complete assembly into a prepared rough opening. A slab door is only the door, so you must match the existing frame, cut or transfer hinge mortises, and fit the latch. Choose the path before removing anything; using slab instructions on a prehung unit, or vice versa, creates avoidable alignment problems.
This guide gives visual checkpoints at every stage: a plumb hinge jamb, even reveals around the slab, a head that is not bowed, and a latch that engages without force. Exact clearances, fasteners, and rough-opening dimensions vary by door model and hardware. Use the selected manufacturer’s instructions for those values rather than applying one measurement to every door.
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Prehung or slab: identify the job first
Look at the replacement before you begin. If hinges are already attached to a rectangular frame, it is a prehung unit. If you have a bare door with no jamb attached, it is a slab. The distinction determines nearly every fitting step.
| Consideration | Prehung interior door | Slab interior door |
|---|---|---|
| What you receive | Door slab, hinges, and jamb assembled together | Door slab only; frame usually remains in place |
| Main work | Fit the entire frame to the rough opening, shim, fasten, and test | Match the existing frame, transfer hinge locations, mortise the edge, and fit latch hardware |
| Existing frame condition | Useful when the old jamb is damaged, missing, or badly out of alignment | Best when the existing jamb is sound, square enough, and worth preserving |
| Hinge mortises | Already cut and attached | Must be marked and cut to match the frame |
| Typical extra tools | Level, framing square, shims, hammer, screwdriver, and finishing nails | Wood chisel or router, drill, and bits for hinge and latch work |
| Primary risk | Installing a frame out of plumb, square, level, or plane | Small errors in hinge height or mortise depth that make the slab bind |
If the old jamb is twisted, split, or substantially out of plumb, a replacement prehung unit is often more predictable than trying to make a new slab work in it. If the frame is solid and its stops and casing are in good condition, a slab can avoid removing finished trim.
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Tools, materials, and a safe setup
Set out the tools before lifting the door. A basic prehung installation typically uses a measuring tape, screwdriver, hammer, four-foot or similarly long level, framing square, wood shims, finishing nails, trim or casing, and the latch or lock hardware. A slab installation adds a sharp wood chisel or router, a drill and bits, and a way to support the door while you fasten hinges.
- Use straight, sound wood shims; cedar shims are suitable for many interior installations.
- Have the manufacturer’s fasteners and hardware instructions at hand. A fastener suitable for a light hollow-core door is not automatically suitable for a heavy solid-core unit.
- Protect the floor and clear a path before moving the assembly.
- Get a partner for a solid-core prehung unit. The frame and slab can be awkward and heavy, and forcing the assembly into position can rack the jambs.
- Keep the door supported whenever you are removing or attaching hinges. Do not let the slab hang from one partially driven screw.
Prepare and inspect the opening
Before setting a prehung door, measure the rough opening and compare it with the door maker’s required dimensions. Check each side and the top with a level, use a framing square where surfaces meet, and look diagonally for signs that the opening is twisted. An opening can appear acceptable from the front yet be out of plane from one corner to the other.
Correct major framing problems before fastening the jamb. A frame that is out of plumb, out of square, or twisted can cause rubbing, uneven gaps, or a latch that misses the strike. Do not rely on a single generic gap measurement: the required opening and operating clearances depend on the specific door, frame, and local conditions.
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For a slab replacement, measure the existing slab and frame separately. Record the door’s width, height, thickness, swing direction, hinge count, hinge heights, and latch location. Check that the replacement slab is compatible with the frame and that the hinge leaves, screw pattern, and stop position can be matched. Photograph or sketch the old hinge and strike locations before removing the old slab so their order is not lost.
How to install a prehung interior door
1. Confirm swing, handing, and orientation
Stand on the intended approach side and decide which way the door should swing and which side will carry the handle. Confirm that the hinge barrels, stop, and latch preparation face the correct direction before raising the unit. A reversed assembly can require removing casing and hardware to fix.
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2. Place the assembly in the opening
Remove shipping clips or temporary braces only when the manufacturer permits it; they often keep the slab aligned during handling. With a partner supporting the weight, guide the unit into the rough opening. Center it as required by the installation instructions and bring the jamb faces into the intended relationship with the wall surface. Keep the slab closed or lightly secured as directed so it does not swing while you work.
3. Set the hinge jamb first
The hinge jamb establishes the door’s vertical reference. Place shims behind each hinge location, not merely at the top and bottom. Check the jamb with the level on both faces and along its edge. Adjust the shims until the jamb is plumb without bowing it toward or away from the opening.
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4. Set the head and latch jamb
With the hinge side stable, inspect the top reveal between the slab and head jamb. If it widens or narrows from one side to the other, adjust the head and the upper hinge-jamb support rather than forcing the door. Add or reposition shims behind the latch jamb at the top, middle, and lower fastening points as needed.
Keep the latch jamb straight in its own plane. A jamb bowed toward the slab can create a tight spot; one bowed away can leave a loose reveal and prevent the latch from reaching the strike. Check the head with a level and use a framing square at the corners. Trade guidance commonly corrects the head margin by adjusting shims at the hinge jamb and then verifies both jambs before final nailing.
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5. Test movement before casing
Open the slab through its intended swing and close it several times. It should move freely without scraping, the reveal should remain reasonably even, and the latch edge should meet the jamb without a shoulder catching. If anything changes as you tighten a fastener, back up, reset the shim, and check plumb again.
Install the latch, handle, and strike using the hardware maker’s hole sizes and placement. Close the door gently and confirm that the latch enters the strike without lifting or pushing the slab. Only after this test should you drive the remaining jamb fasteners, install casing, and complete paint or other finish work. Casing covers the joint; it does not correct a crooked jamb.
How to hang a slab door in an existing frame
1. Transfer the existing geometry
Remove the old door while leaving the jamb undisturbed. Place the old slab over the new one if their sizes match, or use a measuring tape and square to transfer the hinge heights, hinge spacing, top edge, and latch centerline. Mark the intended swing before you mark any cuts. A slab that is the right nominal size can still fail if its hinge pattern is different.
2. Mark and cut hinge mortises
Hold the new slab in the opening with its top and latch-side clearances planned. Transfer each hinge position to the door edge. Outline the hinge leaf with a sharp knife or pencil, then remove the waste with a sharp wood chisel or a router and guide. Work in shallow passes and keep the mortise floor flat.
The hinge leaf should finish flush with the door edge. A mortise that is too shallow leaves the hinge proud and can push the slab away from the jamb; one that is too deep pulls the hinge side in and alters the reveal. Test-fit every hinge leaf before driving screws. Follow the hinge manufacturer’s screw and pilot-hole guidance, and predrill to reduce splitting.
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3. Attach the hinges and support the slab
Fasten the hinge leaves to the slab with the supplied hardware, then support the door at its working height while you align the leaves with the frame. Start all screws before tightening any one of them. Swing the slab slowly and inspect the top, hinge-side, and latch-side reveals. If the door binds, stop and correct the hinge fit or alignment before removing material from the edge.
4. Fit the latch and strike
Use the selected handle set’s template for the bore diameter, backset, and edge-bore location. Drill from both faces when appropriate to limit breakout, then install the latch with its bevel facing the closing direction. Close the door carefully, mark where the latch meets the jamb, and position the strike plate so the latch enters its opening centrally. Secure the strike and test several complete cycles. Hardware dimensions are product-specific, so do not copy a hole size from another handle.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Visual checkpoints that reveal an alignment problem
- Hinge jamb: The level’s bubble stays centered on both faces, and the jamb does not lean when the slab is opened.
- Head reveal: The gap above the slab is consistent from hinge side to latch side rather than forming a wedge.
- Latch jamb: The side gap is straight, with no inward bow at the strike area.
- Door swing: The slab clears the floor and stop through its full travel without a hard spot.
- Latch: The latch enters the strike cleanly without lifting, pulling, or slamming the door.
- Casing: Trim sits against the wall and jamb after operation is correct; it is not being used to hide movement.
Precision matters even when an error looks small. This Old House contractor Tom Silva explains, “Well, over the years, I’ve dropped levels, and, you know, if it’s off just an 1/8 or a 1/16 of an inch, that shows on the door.” The practical lesson is to trust a good level and correct the jamb before the discrepancy becomes visible in the reveals.
Troubleshooting: fix alignment before trimming
The top gap is uneven
Recheck the hinge jamb for plumb, then inspect the head for level and twist. Adjust shims at the upper hinge area and latch jamb rather than sanding the slab immediately. A bowed head or a jamb pulled tight by an overdriven fastener can create the same symptom.
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The door binds on the hinge side
Look for a proud hinge leaf, a mortise that is too shallow, or a jamb that leans toward the slab. On a prehung unit, loosen the nearby fastener slightly, reset the shim, and restore plumb. On a slab, correct the mortise or hinge seating before trimming the edge.
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The latch will not enter the strike
Close the door slowly and identify whether the latch is high, low, or too far toward one side. Check the latch installation direction, the strike location, and the latch-side reveal. Move or shim the jamb only after confirming that the hinges are seated and the slab is not warped.
The jamb moves when the door closes
The fastener may have missed the shim or the opening may be loose around the jamb. Reopen the casing area if necessary, add solid shimming at the load point, and refasten with the product-specified hardware. Do not rely on casing nails to hold a moving jamb.
The opening is twisted or out of plane
Stop before final fastening. Correct the framing where possible or place shims so the jamb faces remain in a usable plane. Manufacturer instructions specifically warn that an opening out of plane can interfere with operation; forcing the slab into that geometry usually transfers the problem to the hinges and latch.
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- Door type, swing, and handle side match the intended room layout.
- Rough opening or existing frame was measured and checked for plumb, square, level, and twist.
- Hinge jamb is supported by shims at hinge locations and remains plumb after fastening.
- Head and latch jamb are straight, with even reveals and no visible bow.
- Slab swings freely, clears the floor and stop, and stays aligned when opened.
- Latch and strike were installed from their hardware instructions and engage without force.
- Only after operation passed were final fasteners, casing, and finish work completed.
Frequently Asked Questions
Can one person install a prehung interior door?
A light hollow-core unit may be manageable, but a solid-core assembly is awkward and heavy. Use a partner for positioning so the jambs are not twisted and the slab is not dropped.
Should I replace the frame or only the door slab?
Keep the frame when it is sound, sufficiently aligned, and compatible with the replacement hinge and latch layout. Choose a prehung replacement when the jamb is damaged, badly twisted, or substantially out of plumb.
What gap should I leave around an interior door?
There is no single safe number for every model. Follow the selected door and hardware manufacturer’s dimensions and clearances, because slab thickness, frame design, flooring, and climate can change the requirement.
Is a chisel required to hang a slab door?
You need a method to make hinge leaves sit flush. A sharp wood chisel works for careful hand-cut mortises; a router with suitable guidance can also be used.
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