Installing an interior pre-hung door is best accomplished with two people, a large box of shims and a box of 10d finish nails.

Step 1: Ascertain that the door opening is 2″ wider and 2-1/2″ taller than the actual door to be installed.

Step 2: Set the door and frame into the opening, positioning it with equal gaps on either side.

Step 3: Use a level along the top of the door jamb to ensure the frame is level. It may be necessary to shorten or shim one leg of the jamb to compensate for settling in older homes.

Step 4: Once the frame is level, insert shims along the top, bottom and middle of the hinged side of the jamb.

Step 5: Hammer one finish nail through the jamb and the top shim to hold the frame in place.

Step 6: Adjust the other shims until the space between the door and the jamb is equal to the full length of the door.

Step 7: Place the level on the inside of the jamb to ascertain the frame is level. Adjust shims as necessary.

Step 8: Place the level on the outer edge of the jamb to ascertain the frame is plumb. Use a section of 2-by-4 lumber and hammer to adjust as necessary.

Step 9: Hammer a 10d finish nail through the jamb and each shim to secure the frame into place.

Step 10: Repeat the process on the latch side of the door. Making adjustments as necessary until the frame is plumb and level on each side.

Step 11: Measure the door opening at the top, middle and bottom to ascertain the jamb is not twisted and the door is square. Open and close the door, making sure it swings freely.

Step 12: Insert two sets of shims along the top of the door jamb. Make necessary adjustments until the gap between the door and the header is even.

Step 13: Fasten the head jamb in place by nailing through the jamb and the shims as before.

Step 14: Recheck to ensure everything is level and square and the door opens and closes freely.

Step 15: Secure the jamb into place with additional finish nails. Score and break away the excess shim material.

Step 16: Fill the nail holes, install the trim and hardware, and shut the door on a job well done.

— Linda Cottin can be reached at LawrenceLiving@ljworld.com.