How To Install An Interior Door That Is Not Pre Hung: 8 Steps

If we remove an existing interior door that has been pre-hung to trim the bottom for a new carpet, it’s a simple matter to align it in position and reattach the hinges. But what happens if you install a new interior door slab that has not been pre-hung previously?

You’ll be glad to know this task is within the ability of a handyperson with a circular saw and a fair amount of patience. However, please note we are talking about replacing an existing door here, not installing a new one in a new frame.

The best way to install an interior door that is not prehung is to:

  • Strip the old door and remove it
  • Prepare the new door for installation
  • Trim the new door to the right size
  • Mark the new door for hinges and handles
  • Cut the new door to size
  • Chisel out the recesses for hinges
  • Hand the new door on the door frame
  • Fit the door lock and handles

What Is A Non-Prehung Door?

A non-prehung is a plain slab door without any mortise lock, door handles, or hinges. It generally doesn’t come with a frame. So you can install it on an existing frame, or will have to purchase and install the frame and jamb separately.

Use the steps below to install your new door if you’re replacing the door slab and can use the old frame as a template. 

Installing a new non-prehung door from scratch is not as simple and is better left to a specialist carpenter to handle.


How To Install An Interior Slab Door

Before getting started, make sure you have the right tools at hand: 

  • Hammer
  • Screwdrivers
  • Chisels
  • Electric drill
  • Set of wood drill bits
  • Sidewinder circular saw
  • Woodworking clamps
  • Long nose pliers

1. Strip The Old Door And Remove It

It’s so much easier to work on a door that’s still in position, as opposed to battling to hold it while working on it at the same time.

  1. Steady the door in the open position at right angles to the door frame. Do this by sliding the outside bottom corner over a wedge, or an old wood chisel tip.
  2. Draw a line with a fine tip indelible marker around the door handles where they touch the door. This will act as a reference point for later.
  3. Remove both door handles by taking out the screws holding them in position. Withdraw the square rod between them if it does not come out by itself

Pro tip: Find a suitable short screwdriver or pair of long-nose pliers that fits in the square slot in the lock and works like a door handle. Pop this tool in your pocket. If the wind slams the door shut while you are inside the room, you cannot be locked out even if the windows are caulked tightly closed!

  1. Remove the screws in the lock face. Insert the square rod through the lock, and gently wobble it until the lock loosens and you can pull it out of the door.
  2. Unscrew the hinges from the old door (not the frame) while an assistant holds it steady. Remove the loose door from the frame and prop it up against a wall.

2. Prepare The New Door For Installation

Lay the new door flat on a convenient level working surface preferably at counter height. Decide which surface is top, bottom, left, and right – you can choose how to install the door, considering that it doesn’t have any recesses yet. 

Lay the old door on top of the new one respecting those conventions. The old door will act as a template for the new one!

Align the two doors to avoid having to trim more than two sides if possible. Don’t be too surprised if the old door is not a perfect rectangle. Door frames seldom are. Decide how best to trim the new door to the old shape.

Remember to allow for a decent cut at both ends, so you do not end up with a wedge that is difficult to finish off neatly. 

Recheck and double-check the result. You don’t want to find yourself with a spoiled door because you rushed the job! When you are confident you have the door correctly positioned, highlight the cut lines with a fine tip indelible marker.

3. Trim The New Door To The Marked Size

We suggest you use a sidewinder circular saw to trim the new door to shape. Here are two ways to achieve this goal:

  • If you have past experience of using the device, you know what to do. Use the tool you already have, or rent one and use a new blade.
  • Speak to a friend, or ask the store where you purchased the door to help you trim it to size. You don’t want to take a chance with a new door!

Mark the new door on the edges so you remember which is top and bottom. Re-label the cut edges as you trim the door so you can’t get confused. Now try the cut door in the door frame. It should be a slightly loose fit on all four sides if you followed our advice.

4. Mark The New Door For Hinges And Handles

You are not on the home run but you are getting there! Lay the new door flat on the convenient level working surface, preferably at the counter height you used before. Put the old door on top of it, making sure to align the top, bottom, left, and right sides correctly.

  1. Clamp the two doors together tightly using woodworking clamps. Remember to use cardboard padding under them so you don’t damage your work surfaces.
  2. Mark the cutout for the hinges on the inside edge of the new door using the fine tip indelible marker. Repeat the process for the lock on the outside edge.
  3. Mark the location of the hole for the square rod that goes between the door handles while you think of it. Aim carefully through the hole in the old door.

5. Cut The New Door To Size

Loosen the woodworking clamps and put the old door to one side. Cut the new door while an assistant holds it steady. Tidy the cut edges with fine-grit sandpaper.

6. Chisel Out The Recesses For The Hinges

You need a sharp chisel for this. Purchase a new one if in any doubt. Lay the door on its side with the marks for the hinges facing up. First, make your cuts around the edges working from the top. Then chisel them out from the side.

  • Remove the hinges from the door frame, and tap them into the recesses you cut.
  • Tidy up your work if needed, drill holes and screw the hinges onto the door.

7. Hang The New Door On The Door Frame

Align the door, with help from an assistant inside the room while you screw the other sides of the hinges onto the door frame. Loosen the screws on the door slightly if it is a tight fit, and then adjust as follows allowing for wood expansion:

  • Bed the hinges further by removing more material if the door catches.
  • Use padding to set the hinges out further if the fit is too loose.

8. Fit The Old Door Lock Into The Frame

Wedge the door open at right angles to the frame as you did before. Drill the hole for the square rod that goes between the two door handles. The door will be hollow at that point. Chisel out for the lock and install it with the screws. 

Fit the door handles and you have a new door to be proud of.


Conclusion

Installing a new door in an old house is a whole lot easier when you use the old door as a template. Mark up the new door so you know how to trim it, and where to chisel out for the hinges and the mortise lock. 

We hope this guide can help you install your non-prehung door like a pro.