Installing Prehung Interior Doors

Installing Prehung Interior Doors

A prehung interior door arrives from the factory as a complete unit: the door slab, hinges, and three-sided jamb assembly are already put together. Your job is to set that unit into a rough opening, make it plumb, level, and square, fasten it securely, and fit the lockset. When the work is done, the door must swing freely through its full arc and latch with no binding or force.

Understanding the Rough Opening

The rough opening (RO) is framed larger than the door unit to allow for shimming and adjustment. A standard interior door unit requires a rough opening that is typically about 2 inches wider and 2 inches taller than the door slab size, but always confirm the manufacturer's specification for the specific unit you are installing. Before setting the unit, check that the RO is plumb, that the floor is level across the opening, and that no fasteners or debris obstruct the jack studs or sill.

Setting the Unit and Shimming

Carry the prehung unit into the opening from the stop side. Center it in the wall thickness so casing can be applied on both faces later. Tack one hinge-side jamb lightly so the unit stays in place while you work.

Shimming sequence:

1. Start at the hinge jamb. Place pairs of composite shims—tapered in opposite directions so they form a flat, solid pack—directly behind each hinge location. Shims must contact both the jamb and the king stud; a gap anywhere lets the jamb flex when the door is used.

2. Place a shim pair near the top and bottom of the latch-side jamb, and one behind the latch strike location.

3. Check the hinge jamb with a 4-foot level on the face of the jamb. Adjust shim depth until the jamb reads plumb. Then check the face of the door stop on the same jamb for a second plumb reading—both readings must pass.

4. Check the head jamb for level. A small wedge under the low-side sill plate area can correct minor floor slopes; otherwise adjust shim thickness at the top corners.

Checking the Reveal

The reveal is the uniform gap visible between the door slab edge and the face of the jamb when the door is closed. Standard interior work calls for a 3/16-inch reveal on all three sides (both side jambs and the head jamb). This gap allows the door to swing without rubbing and looks professional.

Measure the reveal at two points on each side jamb and two points on the head jamb—six measurements total. All six must fall within 1/16 inch of 3/16 inch before you fasten anything. If the reveal is uneven, shift shim depth on the offending jamb until the gap is consistent.

Fastening

Once plumb, level, and reveal are confirmed, drive finish nails through the jamb and shims into the king stud at each shim location. Use a nail set to sink nail heads below the wood surface so filler can cover them. Do not nail through areas where no shim is present—the jamb will flex inward and distort the reveal.

Score each shim flush with the jamb face using a sharp utility knife; snap off the waste. Never use a saw here—the blade can damage the jamb or drywall edge.

Hanging and Checking the Door

If the door was removed for transport, hang it on the hinges now. Swing the door slowly through its full arc, from fully open to the stop. Watch and listen for:

• Binding: the slab rubbing the jamb at any point, which means a jamb is out of plumb or the reveal is too tight.
• Hinge sag: the door dropping toward the latch side at the bottom, which means a hinge leaf is not fully seated or a screw is loose.
• Latch engagement: close the door and confirm the latch bolt snaps fully into the strike plate without lifting or pushing the door.

Installing the Passage Lockset

Use the manufacturer's paper template to mark the centerline of the latch bore (through the face of the door) and the edge bore (through the door edge). Clamp the template securely. Using a door-lock boring kit:

1. Drill the face bore first with the correct-size hole saw, stopping when the pilot bit just breaks through, then finish from the other face to avoid tearout.

2. Drill the edge bore with the correct-size spade or Forstner bit, keeping it perpendicular to the edge.

3. Chisel the mortise for the latch faceplate flush with the door edge.

4. Insert the latch assembly, install the lockset handles, and test full extension and retraction of the latch bolt without force.

Install the strike plate on the latch jamb: mortise it flush, bore the bolt cavity in the jamb, and confirm the bolt seats fully when the door is closed.

Safety

• Wear safety glasses when nailing, drilling, and chiseling—flying chips and nail fragments are the primary hazard.
• Keep fingers clear of the door edge when swinging the slab; a heavy door can crush fingers against the jamb.
• Use a sharp utility knife with controlled strokes away from your body when scoring shims.
• Inspect the boring kit bits before use; a cracked or loose hole-saw arbor can grab and cause hand injury.
• Keep the work area clear of scrap shim material to prevent trips.
• If using a finish nailer, follow the manufacturer's lockout procedure before clearing jams and keep the muzzle pointed away from people at all times.