How to Frame a Prehung Door

For ease and simplicity, installing a prehung interior door is hard to beat. Prehung doors usually consist of the lightweight hollow core door that comes already hinged to the jamb. Hardware such as the door knob and lock may or may not be attached, but some sort of simple clamshell molding is almost always connected to the perimeter of the jamb for ease of installation.

Difficulty: Challenging

Instructions

Things You'll Need:

• Circular saw
• Saw horses
• Carpenter's square
• Four-foot level
• Framing nails ( #16 rosin-coated nails)
• Tape measure
• 2-by-4's
• Reciprocating saw

1. Check the set of instructions that comes with the door; they will give you the exact size of the opening. Prehung doors come as either right-handed or left-handed units. This will determine which way the door opens. Decide whether you want the door to swing into the room or out from the room. Face the doorway, and decide whether you want the hinges to be on the right or left side of the door. Decide this before you build the frame.

2. Put in a double post where you want one side of the door to be, and remember that this double post is the place from which the door will swing, and where the hinges are located. Decide on an already existing upright 2-by-4 as the location for the door opening. Make sure this stud is vertically plumb; if it isn't, loosen one end and re-nail the stud so that it is plumb. Add a second 2-by-4 timber to an already existing upright vertical framing member, and you have the first and most important part of the door frame, the double post.

3. Mark the bottom plate of the wall, where your door is to be located. Consult the manufacturer's guidelines for the size of the opening, and then add 1 1/2 inches to the opening. This is to allow for the other upright 2-by-4. You will be side-nailing the board to the bottom plate, hence the extra 1 1/2 inches. Mark the opening size on the bottom plate.

4. Remove any vertical studs that fall within the door opening with crowbar, and then cut out the section of the bottom plate. A reciprocating saw is necessary for the cut that falls right at the double post, but the other end can be cut with a circular saw and a carpenter's square as a guide. Be sure you set the depth of the saw blade to exactly 1 1/2 inches.

5. Measure the distance from the floor (not the top of the bottom plate) up to the bottom side of the top plate, and cut a 2-by-4 to the exact length. Make sure both ends are square.

6. Place the 2-by-4 at the end of the sawed-off plate, and nail through the vertical framing member into the bottom plate. Make sure this upright is level before you nail the top of the board to the top plate.

7. Measure the distance between the two sides of the door opening, and cut a piece of 2-by-4 to this exact length. Nail it between the double post and the other side of the opening, at the exact height that the manufacturer recommends. You may have to compensate for some extra space at the bottom to allow for a door threshold or wall-to-wall carpet.

8. Add cripples above the door frame. A cripple is a 2-by-4 that fills the space between the top of the door frame and the top plate. Follow the framing pattern (16 or 24 inches on center ) when you nail these pieces into the wall frame.

9. Add a second 2-by-4 to the side of the door frame that you installed last, and be sure it is placed on top of the bottom plate, and nailed tight. Now you are ready to install the prehung door.

Tips & Warnings

• You can leave putting in the double post until after the top part of the door frame is complete. This makes nailing above the door a little bit easier. Make sure both sides of the door are plumb before you begin nailing the top piece in the door frame.
• Make sure all the 2-by-4's that are used around the door opening are straight and solid.