A door that swings freely and which closes with perfect alignment is the goal of any door installation project. Yet doors can be tricky to install. Tolerances are so narrow that it's easy to push the door out of alignment. This invariably leads to sticking doors. Installing a prehung door is one way to increase the chances that your door will work properly.
When to Install a Prehung Door
Doors can be purchased either as slabs or as prehung units. A slab door is simply the door itself—no hinges, frame, or strike plate. A prehung door is a door slab that is already hung by hinges onto a three-sided door frame.
You'll want to install a prehung door for new-construction projects where the doorframe is open to the studs. You will also want to use prehung units for extensive room remodels that require drywall and door framing to be removed and later rebuilt.
Basics of Prehung Door Installation
A prehung door helps the user avoid building out a door frame from scratch—which includes some complicated tasks such as mortising hinges and drilling the door for the door knob.
The rough door opening should have no doorframe. Casing, jambs, doorstops, and all elements of a doorframe should not be in place or should be removed. The prehung door will install directly against the two-by-fours on the sides and on the top (the header).
The rough door opening should always be taller and wider than the height and width of the prehung door unit. This gap is usually 0.5 inch.
Tips For Installing a Prehung Door
While installing a prehung door is easier than building a doorframe from scratch, installation is still a bit trickier than simply inserting the door unit and nailing it into place. Use these tips to make the job go smoother:
- Wait until it is time to install the door to remove the door unit's packing restraints.
- Prehung doors are heavy and unwieldy; always work with a partner.
- Once the restraints have been removed, be careful when handling the door. Prehung door frames prior to installation are delicate.
- The installation is only as good as the condition of the rough opening. Always make sure that it is correctly sized and that the studs are not bowed or damaged.
Equipment / Tools
- Circular saw
- Hand saw
- Tape measure
- Nail set
- Prehung door
- Finish nails
Move the Door to the Site
Acclimate the door in the work area for about 24 hours prior to installation. Lean the door unit against a wall or otherwise keep it vertical. Do not store the door flat.
Inspect the Door
Check the door for signs of damage. Make sure that the door is hanging square and true inside the door frame. Verify that the door is correctly handed for your needs, whether left or right.
Handing refers to the door's swing direction. Right-handed doors open to the right and left-handed doors open to the left.
Prepare the Rough Door Opening
The rough door opening should be correctly built for prehung door installation:
- The height and width must be 0.5 inches greater than the door.
- The opening should be square (check this by measuring both diagonals; the measurements should match or be no more than 0.25 inches apart).
- The header and the floor must be level and flat.
- The side studs should be flat and not bowed or twisted.
- No nails or screws should be protruding from the side studs.
Trim the Jambs as Needed
The sides of the door frame (jambs) may need to be trimmed to allow for the height of the flooring. If the floor is unfinished, generally estimate 2 inches from the top of the unfinished floor to the bottom of the door. If the floor is finished, leave about a 0.5 inch gap at the bottom of the door (or as required by local codes). Trim the bottoms of the jambs as needed or leave as-is.
Level the Hinge Side
Slide the door into position in the door opening. Bring the hinge side of the door to level. Temporarily nail into place with shims and finish nails.
Level the Latch Side
Level the latching side of the door. Nail into place with shims and finish nails.
Shim the Top
Place a shim at the top of the door unit, just below the header, and nail it into place with finish nails.
Shim and Nail for Square
With the tape measure, check both diagonals for door frame square. Shim as necessary to bring the door frame back into square.
Add the Rest of the Shims
If the door is correctly positioned, nail shims every 12 inches or so. Trim off the shims with the handsaw.
When to Call a Professional
In most cases, prehung doors should be installed by experienced carpenters. Installation can be tricky, and an expert who is proficient at the task can save you time and money overall. If you're not confident in your carpentry skills or run into problems early on in the project, consider calling a professional.