How to install an interior door

Installing an interior door is a rewarding project that can transform the look and feel of your living spaces. Interior doors can create a sense of privacy, define room boundaries and enhance the overall aesthetic of your home.  
 
The process may seem daunting at first, but with the right guidance and preparation, installing an interior door is achievable for the average homeowner.  
 
In this article, we’ll provide you with the steps you need to confidently install your own flat jamb prehung interior door.  

How to install a flat jamb prehung interior door 

When it’s time for a new door, you have the option of either a prehung door or a slab. Prehung doors include a slab with hinges already attached to the frame for each installation, while a slab is just the door.

Follow these steps to measure for a new flat jamb prehung interior door:  

1. Gather all equipment

For this project, you'll need: 

• Pencil
• Piece of paper
• Flat jamb prehung door unit
• Level
• Shims
• Screwdriver
• Hammer
• #8 2 ½" finish screws (for solid core doors)
• #8 finishing nails (for hollow core doors) 
• #6 finishing nails
• Door casing
• Door hardware and accessories
• Safety glasses
• Safety gloves

2. Remove the existing door and its frame  

Before getting started on this project, it’s important to have measurements. Read our article on how to accurately measure for an interior door before beginning, then follow these steps:  

• Once you’re ready to install your new interior door, it’s time to remove the existing door and its frame down to the rough opening. If you haven’t already, remove both sides of the casing that surrounds the door with a flat pry bar. Take extra care if you plan to reuse it. 
• Remove the hinge pins using a screwdriver and hammer, then remove the door from the frame. 
• Remove the hinge plates and strike plates using a screwdriver. 
• Remove the side jambs, then pry down the head jamb. If you want to make any changes to the wall or frame, like painting, now’s a great time to do that.

3. Position the prehung door

Prehung doors, especially solid core ones, can be heavy and difficult to maneuver alone, so you might want some help for this part. Here is how to position your prehung door:  

• Begin by centering the door in the rough opening.  
• With your installation partner, align the door so the jamb is flush with the wall. 
• Double check that the handle is on the correct side and that the door will swing in or out of the room as intended. 

4. Level the door and secure the jamb to the rough opening 

Here is the process to follow to complete this step:  

• Place shims between the door jamb and studs behind each hinge so that the door is plumb and stays centered in the opening. 
• Align the level to the back side of the jamb to ensure it is plumb.  
• Move the level to the interior face of the jamb to ensure it’s also plumb in that direction. If it’s not, adjust the shims as needed. 
• On the hinge side, fasten the frame to the rough opening at each shim location using finishing nails or finish screws. For standard hollow core doors, you’ll need #8 finishing nails, and for heavier doors like solid core doors, you’ll need to use #8 2 ½” finish screws.  
• Drive two nails or screws through the frame, through the shims and into the studs about an inch from each edge. It’s important that the nails or screws are embedded into the studs for security. 
• Shim the latch side so it’s aligned evenly with the wall, with the door hanging vertically straight and level within the frame. Ensure that there is enough spacing between the door, the latch jamb and the head jamb. If the gap at the top of the door is uneven, adjust the position of the latch jamb up or down until the gap is even and the door opens and closes smoothly. Confirm that the gap under the door is 7/8” or more from the top of the flooring to the bottom of the door. 
• Use two #8 finishing nails or #8 2 ½” finish screws, depending on the door, driving them through the frame, through the shims and into the studs, about an inch from each edge. If any of the shims stick out past the jamb, score them with a utility knife and break along the line. 

5. Install the door casing

To install the door casing, set the door casing around the door and nail it in place on the jamb and studs. Then, drive #6 finishing nails through the casing and into the studs, spacing the nails about 16 inches apart. 

6. Attach the door hardware and accessories

Now that the door is hung, install the backplates, doorknobs and strike plate. Be sure to follow the hardware manufacturer’s installation instructions. Then, caulk and paint your casing. 
 
Congratulations! You have installed your new interior door.