Replacing a door is a straightforward DIY project when you use a prehung door — the door comes already mounted in a frame, which eliminates the most difficult part of the job. Expect 2–4 hours for an interior door and 4–6 hours for an exterior door. This guide covers measuring, removing the old door, installing the new one, and the key differences between interior and exterior replacement.
What You’ll Need
- Prehung door (interior or exterior, measured to fit your rough opening)
- Hammer and pry bar
- Reciprocating saw or utility knife (for cutting casing nails)
- Level (4-foot minimum)
- Tape measure
- Drill and drill bits
- 3-inch exterior screws or 16d nails
- Shims (cedar shims recommended)
- Caulk gun and exterior caulk (for exterior doors)
- Insulating foam (for exterior doors)
- Putty knife and finishing nails (for casing trim)
- Safety glasses and work gloves
Safety & Precautions
- Exterior doors are heavy — get a helper. A standard exterior door weighs 60–100 lbs. Attempting to set it alone risks injury and damage to the door frame. Interior doors (25–50 lbs) can often be managed solo with care.
- Check for structural headers before removing. Door openings have a structural header above them. Never remove framing without confirming the header is in place and undamaged.
- Wear safety glasses when cutting nails. A reciprocating saw cutting through casing nails sends metal fragments in unpredictable directions.
- Confirm utility lines are not in the wall. While rare in door openings, verify no electrical or plumbing runs through the specific wall section before cutting.
- For exterior doors: work on a dry day. Leaving an exterior opening exposed to rain even briefly can damage flooring, subfloor, and framing.
Step 1 — Measure Your Rough Opening
Before purchasing a replacement door, measure your rough opening accurately. The rough opening is the framed hole in the wall — not the door itself.
- Measure the width from stud to stud inside the existing frame (after removing casing trim)
- Measure the height from the subfloor to the top of the rough opening
- Standard interior door sizes: 24″, 28″, 30″, 32″, 36″ wide × 80″ tall
- Standard exterior door sizes: 32″ or 36″ wide × 80″ or 96″ tall
- The prehung door unit you buy should be 2″ narrower and 2″ shorter than your rough opening — this allows room for the frame and shimming
- Also note door swing direction: stand inside the room facing the door opening — if hinges are on the left, it’s a left-hand swing; right hinges = right-hand swing
Step 2 — Remove the Old Door and Frame
Remove the Door from Its Hinges
Open the door fully. Use a hammer and screwdriver to tap out the hinge pins from the bottom up. Lift the door off the hinges with a helper. Set it aside flat to avoid warping or falling.
Score and Remove the Interior Casing
Use a utility knife to score the paint line where the casing meets the wall on both sides of the door. Slide a putty knife behind the casing and gently pry it away from the wall. Work slowly to avoid damaging drywall — you’ll likely reuse or replace this trim after the new door is installed.
Remove the Old Door Frame (Jamb)
Use a reciprocating saw to cut through the nails holding the door jamb to the rough framing. Cut along the edge of the jamb on both sides and across the top. Then use a pry bar to pull the jamb sections away from the rough opening. Remove any remaining nails and clean up the rough opening.
For Exterior Doors: Also Remove Exterior Casing and Flashing
Outside the house, use a utility knife to cut the caulk line around the exterior casing, then pry it away. Remove any existing flashing or door pan if present — you’ll install new with the replacement door. Inspect the rough sill for rot or water damage and repair before installing the new door.
Step 3 — Prepare the Rough Opening
- Remove all nails, staples, and debris from the rough opening
- Check that the rough sill (bottom of the opening) is level — this is critical; an unlevel sill means shimming problems throughout the installation
- For exterior doors: install a door pan (sill pan flashing) at the bottom of the rough opening to prevent water intrusion. This step is frequently skipped and is the primary cause of future rot at the door sill
- Check that the rough opening sides are plumb using your level
- If the rough opening is significantly out of plumb or level, sister additional framing lumber alongside the existing studs to create a plumb, square opening
Step 4 — Set the Prehung Door Unit
Tip the Door into the Opening
With a helper, tip the prehung door unit into the rough opening from the outside (for exterior) or from either side (for interior). The door should fit inside the opening with the jamb face flush with or slightly proud of the finished wall surface. Have your helper hold the door plumb while you begin shimming.
Shim the Hinge Side First
The hinge side of the door sets the standard for the entire installation — get this side perfectly plumb and it makes everything else easier. Place pairs of shims (pointed end in opposite directions) behind the jamb at each hinge location. Check with your level and adjust shims until the hinge side jamb is perfectly plumb. Drive one 3-inch screw through the jamb and shims into the framing stud at each hinge location — but don’t fully tighten yet.
Check the Reveal and Shim the Latch Side
Open the door and check that the gap between the door and the jamb (the “reveal”) is consistent — ideally about 1/8 inch all the way around. Shim the latch side jamb at the top, middle, and bottom until the reveal is even and the latch side is plumb. Add shims at the top corners as well.
Test the Door Operation
Before driving all fasteners, open and close the door several times. It should swing smoothly without binding, latching should feel positive, and the reveal should remain consistent. If the door binds at the top or drags at the bottom, adjust your shims before proceeding.
Drive All Fasteners
Once the door operates correctly, drive 3-inch screws through the jamb and shims into the framing at all shim locations. Score or snap the shims flush with a utility knife. For exterior doors, also drive screws through the hinge-side jamb in the pre-drilled security screw locations (3″ screws into the framing — not just the jamb).
Step 5 — Finishing: Interior vs. Exterior
Interior Door Finishing
- Install door casing trim on both sides, nailing through the casing into the jamb and the rough framing
- Fill nail holes with wood filler, sand smooth, and paint or stain to match
- Install the door hardware (knob, latch plate, strike plate) per the manufacturer’s instructions
- Adjust the strike plate if needed so the latch engages cleanly
Exterior Door Finishing
- Apply a continuous bead of exterior caulk between the brick mold/exterior casing and the siding on all sides
- Inject low-expansion foam insulation (not standard expanding foam — it can bow the jamb) into the gaps between the jamb and rough framing on all sides
- Install the exterior door hardware: handle set, deadbolt, and door sweep
- Install a door threshold if not included with the prehung unit
- Paint or prime the door and exterior casing before heavy weather exposure
For secure door hardware installation, see our guides on how to install a deadbolt and door handle replacement.
Interior vs. Exterior Door Replacement: Key Differences
| Factor | Interior Door | Exterior Door |
|---|---|---|
| Typical cost (DIY) | $100–$400 | $300–$1,200+ |
| Weight | 25–50 lbs | 60–100+ lbs |
| Door material | Hollow core or solid wood | Steel, fiberglass, or solid wood |
| Installation time | 2–4 hours | 4–6 hours |
| Weatherstripping needed | No | Yes — included or installed separately |
| Sill pan flashing | No | Yes — critical for water protection |
| Requires helper | Optional | Strongly recommended |
| Permit required | Usually no | Sometimes — check local codes |
When to DIY vs. Hire a Pro
- DIY-friendly: Standard-sized prehung interior door in a square, sound rough opening
- DIY with care: Standard exterior door replacement in a straight, undamaged rough opening
- Call a pro: Non-standard sizes, out-of-square rough openings, visible rot in the framing, structural header concerns, or if you need to move the door location entirely
- Permit consideration: Replacing a door in the same location typically doesn’t require a permit in most jurisdictions, but moving a door or expanding the opening usually does
Pro Tips
- Never use standard expanding foam on exterior door jambs. Regular expanding foam exerts enough pressure to bow the jamb inward, causing the door to bind. Use “minimal expanding” or “window and door” foam only.
- The hinge side sets everything. If your hinge side jamb isn’t perfectly plumb, the entire door will be off. Spend extra time getting this right before moving to the latch side.
- Buy a prehung door, not a slab. Slab door replacement (door only, no frame) is significantly more difficult and requires precise fitting, planing, and hinge mortising. Unless you’re a skilled woodworker, a prehung unit is worth the extra cost.
- Check the rough opening for square. Measure diagonally corner to corner in both directions — if the measurements are equal, the opening is square. A difference of more than 1/4 inch will require extra shimming work.
Frequently Asked Questions
Can I replace a door myself with no experience?
Yes — interior prehung door replacement is one of the most beginner-friendly home improvement projects. The door comes pre-hung in a complete frame, so you’re primarily focused on shimming it plumb and level rather than any complex carpentry. Most homeowners with basic tool comfort can complete it in an afternoon.
How do I know what size replacement door to buy?
Measure the width and height of your rough opening (the framed hole, not the existing door). Your new prehung door unit should be approximately 2 inches narrower and 2 inches shorter than the rough opening. The standard door height is 80 inches; standard widths are 24, 28, 30, 32, and 36 inches. When in doubt, bring your measurements to the door department at Home Depot or Lowe’s — they can help you select the correct unit.
Do I need a permit to replace a door?
In most US jurisdictions, replacing a door in its existing location with the same size does not require a permit. However, enlarging the rough opening, moving the door location, or replacing an exterior door in some municipalities may require one. Check with your local building department before starting — the penalty for unpermitted work can complicate home sales later.
How long does it take to replace a door?
An interior prehung door replacement takes 2–4 hours for a DIYer working carefully. An exterior door takes 4–6 hours. Add time for removing old paint, repairing rough opening damage, or casing and trim work after installation.
What’s the difference between a prehung door and a slab door?
A prehung door comes with the door already mounted on hinges in a complete frame (jamb). You install the entire unit into the rough opening. A slab door is just the door panel — no frame, no hinges. Slab replacement requires removing the old door while keeping the existing frame, then fitting, mortising, and hanging the new door in that frame. Slab replacement is more complex and only practical when the existing frame is in perfect condition and the door is a standard size.
Conclusion
Replacing a door is a rewarding project that dramatically changes the look and function of a room or entry. Use a prehung door unit, take time to get the hinge side perfectly plumb, and test the door operation before driving all your fasteners. For exterior doors, don’t skip the sill pan flashing and minimal-expanding foam — these two steps prevent the water damage that causes most exterior door failures.
Related guides: how to fix door hinges, how to weatherstrip a door, and our full interior and exterior door types guide to help you choose the right replacement door.
