Measure the door frame. Use a tape measure and square to check the dimensions and angles of the door frame (the opening in the wall where your door will go). The door frame must be 2 inches wider than the door and 1 or 2 inches taller, and corners should be 90 degrees. If necessary, you may be able to adjust the width, height or angles by tapping boards with a hammer or placing wood shims. If this doesn't resolve the issue, you may have to reframe the doorway.
Set the door. Place the pre-hung door into the door frame. On the hinge side, use a level to ensure the door is exactly vertical. If necessary, use a pry bar and wood shims (placed between the door frame and jamb) to level the door. Measure the gap between the door frame and jamb at several spots to make sure it is the same all around.
Attach the hinge side. Place a wood shim between the door frame and jamb close to the highest hinge, and nail through both. Repeat this step with new shims for the other hinges, and add nails as needed to securely attach the door. To prevent future warping or twisting, put a shim in place anywhere you nail through the jamb.
Attach the latch side and top. Check to be sure the door is still square and level in the door frame, and then repeat step 3 for the latch side and top of the door.
Attach trim. Use a handsaw to trim any shims sticking out beyond the doorframe. Place casing, or trim, around the door to cover the space (and shims) between the jamb and the door frame. Measure in several places to be sure the reveal (the amount of jamb visible past the inside edge of the trim) is the same everywhere. Use a level and square to confirm that casing pieces are aligned properly and meet at the right angles. Then attach the trim using 4d finish nails.
Attach knob. If the door doesn't have a knob already in place (as most won't), use the pre-cut holes to install a doorknob and latch according to the manufacturer's directions.
Things You Will Need
- Pre-hung door
- Finish nails (4d and 8d)
- Saw (hand or crosscut)
- Pry bar
- Wood shims
- Tape measure
- Consider both flat- and split-jamb doors. Flat-jamb pre-hung doors require fewer steps to install, but you will need to place and attach the trim (casing) separately. Split-jamb doors take a little longer to install, but the trim is already in place and properly positioned. Be sure to select a door that meets your needs. Hollow-core doors are lighter and cost less, while solid wood and solid-core doors are sturdier and dampen sound more effectively.