A pre-hung door arrives as a complete unit: door, hinges already installed in the jamb, jamb pre-cut to standard sizes. The install replaces an existing door and frame in one shot — much easier than building a frame from scratch and hanging the door separately. The job depends on getting the rough opening straight and shimming the jamb plumb and level.
This guide covers a standard interior pre-hung door swap — taking an existing door and frame out, installing a new pre-hung in the same opening. Exterior doors are similar but require flashing and weatherproofing covered separately.
Before you start
Three things to settle:
1. Match the rough opening size. Pre-hung doors come in standard widths (24, 28, 30, 32, 36 inch — actual door size, not rough opening) and standard heights (80 inch). Rough opening is typically the door size + 2 inches in each direction (so a 32-inch door needs a 34x82 inch rough opening). Measure your existing rough opening and order matching size.
2. Right-hand or left-hand swing. Stand outside the room facing the door. If the hinges are on your right and the door swings into the room toward your left, it's a right-hand door. Hinges on left, swings right = left-hand. Order matching the existing — wrong hand means re-mounting hardware or returning.
3. Jamb width. Standard interior jamb depth: 4-9/16 inch (matches 2x4 wall plus drywall both sides). Some walls are thicker (2x6 framing or with insulation extras) requiring deeper jambs. Measure the wall thickness from drywall surface to drywall surface; pick a jamb that matches.
What you'll need
Tools
- Hammer
- Pry bar
- Screwdriver and drill
- Level (4-foot or 6-foot)
- Tape measure
- Speed square
- Reciprocating saw (for removing old jamb)
- Utility knife
- Caulk gun (optional, for finished trim)
- Wood shims (cedar wedges or plastic)
- Finish nailer or hammer + finish nails
Materials
- Pre-hung door unit (matching size, hand, jamb depth)
- Wood shims
- 10d or 16d finish nails (for jamb to framing)
- 1.5-inch trim screws (alternative to nails for jamb)
- Construction adhesive (for trim, optional)
- Door knob/lever (if not included with door)
The hinge side gets shimmed first
Pre-hung doors install in a specific order: hinge-side jamb first, plumb and shimmed; then strike-side jamb adjusted to match the door's swing.
If you set the strike side first, the hinge side ends up off-plumb and the door binds when closing or rubs the head jamb.
Step-by-step instructions
Remove the existing door and frame
Pop the hinge pins on each hinge. Lift the door free of the jamb.
Remove existing trim (casing) on both sides of the wall — pry off carefully if you plan to reuse.
Remove the jamb. Most are nailed to the rough opening through the jamb sides. Cut nails with a reciprocating saw or pry the jamb free.
Inspect and prep the rough opening
Look at the rough opening (the framed wall opening before any jamb). Verify:
- Sized correctly: rough opening should be door width + 2 inches and height + 2 inches.
- Plumb: sides should be vertical. Use a level to check.
- Square: diagonal measurements should match.
- If the rough opening is significantly out of plumb or square, framing modifications may be needed before the new door can install correctly.
Insert the pre-hung unit
Slide the pre-hung door into the rough opening. Centre it left-right; it should sit on the floor with the jamb extending up to the head.
Have a helper hold the unit upright while you start shimming.
Shim and plumb the hinge side
On the hinge-side jamb, slide pairs of cedar shims behind the jamb at each hinge location (3 hinges = 3 shim positions). Adjust shim depth until the jamb is plumb (use a 6-foot level against the jamb).
Drive 16d finish nails through the jamb, through the shims, into the rough opening's stud. Two nails at each shim position.
Verify plumb with the level — if it shifted during nailing, back the nails out and re-shim.
Adjust strike-side jamb
Close the door. Look at the gap between the door's edge and the strike-side jamb — should be uniform 1/8 inch top to bottom.
If the gap varies, shim the strike-side jamb in or out at problem points until uniform.
Drive nails through the strike-side jamb at each shim position once the gap is uniform.
Shim and nail the head jamb
Verify the head jamb is level (top of jamb).
Slide shims above the head jamb (between jamb and rough opening) at 2-3 positions. Adjust shim depth until level.
Drive finish nails through the head jamb into the rough opening's header.
Verify door operation
Open and close the door fully. The door should swing smoothly, not bind on the head, sides, or floor.
If it binds: identify where (top, bottom, side) and adjust the corresponding jamb's shim position.
Continue adjusting until the door operates smoothly through full swing.
Trim shims flush with the jamb
Score shims with a utility knife along the jamb's edge, then snap off excess. Shims should be flush so trim casing sits flat against the jamb.
Install trim casing
Casing (the trim around the door frame on each side of the wall) is usually pre-cut to fit the standard pre-hung jamb.
Mitre cuts at the top corners (45 degrees), butt joints at the bottom against the floor.
Nail trim to both the jamb (3-4 nails per piece) and the rough framing behind.
Install door hardware
If the door doesn't include a knob, install one — see our 'How to Replace a Door Knob' guide for the bore prep and installation.
Adjust the strike plate on the jamb so the latch engages cleanly when the door closes.
Common mistakes that cost you
- Skipping rough opening verification. If RO isn't square/plumb, the door won't install correctly regardless of shimming. Check before installing.
- Setting strike side first. Hinge side must be plumb first; strike adjusts to match. Wrong order means door binds.
- Insufficient shimming. Long-term door problems trace back to shim under-shimming. Use 3 shim positions per side minimum.
- Wrong jamb depth. Jamb deeper than wall produces extension issues; shallower exposes framing. Match jamb depth to wall thickness.
- Wrong door hand. Right-hand vs left-hand wrong means re-mounting all hardware. Order based on existing.
Frequently asked questions
What's a 'pre-hung' door?
A pre-hung door comes as a complete unit: door already mounted in its jamb (frame), with hinges installed, hardware bored. It's ready to install in a rough opening.
Alternative is 'slab' door — just the door, no frame. Slab requires existing jamb in good condition; pre-hung is far more common for residential.
How do I know if my door is right-hand or left-hand?
Stand outside the room facing the door. If hinges are on your right, it's a right-hand door. Left = left-hand.
Order matching what's there. Wrong hand requires re-mounting all hardware (possible but adds work).
Can I install a pre-hung in a rough opening with no existing door?
Yes — the rough opening just needs to be sized correctly (door width + 2 inches, height + 2 inches). If the rough opening doesn't exist yet, you're framing it from scratch, which is more involved.
When to call us instead
If your rough opening is out of square, you're upgrading from a hollow-core to solid door, or you're working on exterior doors with weatherproofing requirements, this becomes more involved. We handle door installation as part of larger renovation work.
Book a free 60-minute site visit →Related Ottawa services
If you're updating doors and trim throughout a renovation, our residential renovation team handles doors, trim, and hardware as fixed-price work. Book a free 60-minute consultation.