Installing a Prehung Door

When ordering doors you will probably end up in a discussion about right- and left-hand doors. This can be confusing, in part because locksets and doors use the same terminology in slightly different ways.

For doors: If the hinges are on the left when you pull the door open, it is a left-handed door, as shown above left. If the hinges are on the right when you pull the door open, it's a right-handed door.

For locksets the hand is determined from outside the room. If the door swings into the room and the hinges are on the left, the lockset is left-handed, as shown above right. If the door swings out of the room and the hinges are on the left, the lockset is left-hand reverse. If hinges are on the right, the door can be right-hand or right-hand reverse.

The best way to avoid confusion is to show diagrams of what you want to your supplier.

When prehung doors are assembled, the hinge screws sometimes poke through the back of the jamb. If your rough opening is tight or out of plumb, these can catch. Back them out slightly and try again.

A common problem when installing a prehung door is a twisted jack stud. Even if you carefully select framing lumber and craft the wall frame accurately, studs can move as they adjust to conditions in the house. The result often is a door opening that isn't true. If you attach a door frame to a twisted jack stud, it will look as though the door is standing partially open; actually, the entire door frame will be protruding into the room.

You can force the frame back into the plane of the wall, but you'll risk damaging the frame. Instead, add a third shim and tap it in until the frame is square.

To install door frames efficiently, you need a long level. A 48-inch model is adequate, but a 72-inch level is the best tool to use. If you don't want to invest in either of these tools, there is another approach. Instead of a level you can use a plumb bob to check whether the jambs are plumb and straight. To use this method, secure the hinge-side jamb to the jack stud with three pairs of shims. Drive a 16d finishing nail partially into the jamb near the top (the stop will eventually cover the hole). Hang a plumb from the nail so it dangles almost to the floor. Adjust the shims until the gap between the jamb and the string is equal from top to bottom. Pin the shims in place with 8d finishing nails.

Hang a plumb bob alongside a door jamb to give yourself an immediate reference for plumbing the jamb. This simple tool eliminates the need for a long level when installing doors.

Adjust the shims behind the jamb until the distance from the jamb to the string is equal all along the length of the jamb. Add pairs of shims if necessary to compensate for a warped jamb.