How to Replace an Interior Door
- Staff Desk
- 6 hours ago
- 8 min read
Have you ever looked at a door in your home and felt like it belonged in a different decade? Maybe it has a hole in it, it’s scratched up from a pet, or it just won’t stay closed no matter what you do. Replacing an interior door is one of the most rewarding "big" DIY projects a homeowner can tackle. It instantly changes the look of a room and makes your house feel newer and more functional.
The best part? You don't need to be a master carpenter to do it. While it might seem scary to take a door off its hinges, this blog will show you how to replace an interior door using very simple steps and common tools.
Table of Contents
Slab vs. Pre-Hung: Which One Should You Choose?
The Complete Tools and Materials Checklist
Safety First: How to Stay Protected
Phase 1: Removing the Old Door
Phase 2: Measuring Like a Pro
Phase 3: Preparing the New Door (Slab vs. Pre-Hung)
Phase 4: Installation and Leveling
Phase 5: Hardware and Final Tweaks
Common Mistakes and How to Fix Them
Advanced DIY Tips for Tricky Doors
Frequently Asked Questions (FAQs)
Conclusion: You’ve Got This!
1. Slab vs. Pre-Hung: Which One Should You Choose?
Before you go to the hardware store, you need to make a big decision. There are two main ways to buy a door.
The Slab Door
A slab door is just the door itself. It is a flat piece of wood or composite material. It does not come with hinges, a frame, or a hole for the doorknob.
Choose this if: Your current door frame is in perfect condition (not warped or broken) and you want to save money.
The Challenge: You have to "match" the new door to the old frame. This means you have to cut out the spots for the hinges yourself and drill the hole for the knob.
The Pre-Hung Door
A pre-hung door comes already attached to its own frame. It’s a "door-in-a-box" kit.
Choose this if: Your old frame is damaged, or if you want the easiest installation possible.
The Challenge: You have to remove the old frame and the decorative wood (trim) around the door. It is a bigger job at first, but it is much easier to get the door to swing perfectly.
Most beginners find that a pre-hung door is actually easier to get right, even though it involves more steps!
2. The Complete Tools and Materials Checklist
You don’t want to be halfway through a project and realize you’re missing a tool. Here is exactly what you need.
Essential Tools
Tape Measure: For getting those exact numbers.
Level: This is your most important tool. It tells you if your door is perfectly straight.
Hammer and Nail Set: To pop the hinge pins out.
Screwdriver or Power Drill: For all the screws.
Chisel: If you are doing a slab door, you’ll need this to carve out space for the hinges.
Utility Knife: To cut through old paint or caulk so you don't rip the drywall.
Pry Bar: To pull off the old trim.
Essential Materials
New Door: (Slab or Pre-hung).
Wood Shims: These are thin, wedge-shaped pieces of wood. They are the secret to a straight door.
Finish Nails: To secure the frame or trim.
New Hardware: Hinges, doorknob, and the latch set.
Wood Glue/Wood Filler: To fix any small mistakes.
3. Safety First: How to Stay Protected
DIY is fun, but safety is serious. Follow these three rules:
Protect Your Eyes: Small splinters of wood can fly when you are drilling or hammering. Always wear safety glasses.
Ask for Help: A solid-core door can be very heavy. Don't try to lift it into place by yourself—ask a friend to hold it steady while you set the screws.
Watch Your Fingers: When you are setting a door into a frame, it is very easy to pinch your fingers. Work slowly.
4. Phase 1: Removing the Old Door
Let’s get started. To put the new door in, the old one has to go.
Removing a Slab Door
Close the door. This keeps it from falling on you.
Pop the pins. Put a nail or a small screwdriver at the bottom of the hinge pin. Tap it upward with a hammer until the pin pops out of the top.
Lift the door. Carefully open the hinges and lift the door away. Set it aside.
Removing a Pre-Hung Door (Including the Frame)
Remove the door using the pin method above.
Cut the caulk. Use your utility knife to slice the line where the wood trim meets the wall. This prevents the paint from peeling off the wall.
Pry off the trim. Gently slide your pry bar behind the trim and pop it off. Keep it if you want to reuse it!
Cut the nails. Use a saw or just pry the frame away from the wall studs. Once the frame is loose, pull the whole thing out of the opening.
5. Phase 2: Measuring Like a Pro
If you get the measurements wrong, the door won't fit. This is where many people fail, but you won't!
Measuring for a Slab Door
Measure the old door itself.
Measure the width (top, middle, and bottom).
Measure the height.
If the old door was 30 inches wide, buy a 30-inch door.
Measuring for a Pre-Hung Door (The "Rough Opening")
You need to measure the hole in the wall, not the door.
Width: Measure from one wood stud to the other. Do this at the top, middle, and bottom. Use the smallest number.
Height: Measure from the floor to the bottom of the wood header at the top.
Wall Thickness: Measure how deep the wall is (usually 4.5 inches). This ensures the new frame is wide enough.
Pro Tip: Your "Rough Opening" should be about 2 inches wider than the door itself to give you room for adjustments.
6. Phase 3: Preparing the New Door
Pathway A: Preparing a Slab Door
Since a slab door is a blank canvas, you have work to do:
Trim to size: If the new door is slightly too tall, you may need to trim the bottom with a circular saw.
Mark the hinges: Lay your old door on top of the new one. Mark exactly where the hinges are.
Chisel the "Mortise": Use your chisel to carve a shallow hole for the hinge to sit in. It should be flush with the wood.
Drill the knob hole: Use a "door hole saw kit" (available at any hardware store) to cut the perfect hole for the handle.
Pathway B: Preparing a Pre-Hung Door
This is easy! Most pre-hung doors are ready to go. You just need to remove any shipping brackets or plastic clips that are holding the door closed during travel.
7. Phase 4: Installation and Leveling
This is the most critical part of how to replace an interior door. If the door isn't "level" and "plumb," it will swing open or closed on its own.
The "Shimming" Secret
A wall is almost never perfectly straight. We use wood shims to fill the gaps between the door frame and the wall studs.
Place the door in the opening. Stand it up and center it.
Focus on the hinge side first. Use your level on the side where the hinges are. Slide shims behind the hinges until the level says the frame is perfectly straight (plumb).
Screw it in. Once it is straight, drive screws through the frame and shims into the wall.
Repeat on the other side. Add shims to the "latch side" so the gap between the door and the frame is even all the way around (about 1/8th of an inch).
Check the swing. Open and close the door. Does it catch? Does it stay where you put it? If yes, you are doing great!
8. Phase 5: Hardware and Final Tweaks
You’re almost to the finish line!
Install the Doorknob: Slide the latch into the side hole first, then put the two halves of the handle through. Tighten the screws by hand so you don't strip them.
Install the Strike Plate: This is the metal plate on the frame that the latch clicks into. If the door doesn't stay shut, you might need to move this plate up or down slightly.
Cut off the shims: Use your utility knife to score the shims where they stick out past the wall. Snap them off so they are flush with the drywall.
Put the trim back on: Nail the decorative wood (casing) back around the door to hide the shims and the gap.
9. Common Mistakes and How to Fix Them
Even pros make mistakes. Here are the big ones to watch out for:
Mistake: The door hits the floor.
The Fix: If your carpet is too thick, you’ll need to take the door off and trim 1/4 inch off the bottom with a saw.
Mistake: The "Ghost Door" (swings by itself).
The Fix: This means the top of the door is leaning in or out. Use your level and adjust your shims to make the hinge side perfectly vertical.
Mistake: Gaps are uneven.
The Fix: If the gap at the top is wide on one side and narrow on the other, your frame is "racked." Loosen the screws on one side and shift the frame up or down.
Mistake: Screwing through the gap without shims.
The Fix: If you just drive a screw into the gap, it will bend the frame and the door won't close. Always have a shim where you put a screw.
10. Advanced DIY Tips for Tricky Doors
What if the wall is warped?
In older homes, walls are often "bowed." If your door frame won't sit flat against the wall, you might need to "cross-set" the frame. This involves pushing the top of the frame in and pulling the bottom out slightly.
Custom Trimming
If you live in an old house with short doors, a standard 80-inch door won't fit. You can cut up to 1 inch off the bottom of most hollow-core doors. If you need to cut more, you might need to buy a solid wood door, which can be trimmed as much as you like.
To Paint or Not to Paint?
Always paint or stain your door before you install it. It is much easier to paint a door while it is laying flat on two sawhorses than it is to paint it while it is hanging. Don't forget to paint the very top and very bottom edges to prevent the wood from warping!
Frequently Asked Questions (FAQs)
Q: How long does it take to replace a door?
For a beginner, a pre-hung door takes about 2 to 3 hours. A slab door might take 3 to 5 hours because of the chiseling and drilling.
Q: Can I reuse my old hinges?
You can, but new hinges are cheap and will look much better with your new doorknob.
Q: Do I need a special drill for the doorknob?
You just need a standard power drill. You will need a "Hole Saw" attachment, which you can find in a "Door Lock Installation Kit" for about $15.
Q: What if my house is really old and the sizes are weird?
You can order "custom sized" doors at most home centers. It costs a bit more, but it saves you hours of frustration.
Conclusion: You’ve Got This!
Replacing an interior door is a rite of passage for any DIYer. It requires patience and a good level, but the result is a home that feels more polished and cared for. Remember: Measure twice, shim carefully, and don't be afraid to ask for a second pair of hands. Once that door clicks shut perfectly for the first time, you’ll feel a massive sense of pride.
Now that you know how to replace an interior door, what’s next? You might want to learn how to install crown molding or how to upgrade your baseboards to match your beautiful new doors.