Hanging Prehung Doors in Misaligned Door Framing

Insert the prehung door into the rough opening.

Insert two shims into the spaces between the door frame and the inside face of the rough opening. Put in a shim from the exterior and another from the interior face so the shims overlap, making a bearing surface against the exterior face of the door frame.

Continue placing two shims spaced every 12 inches around the outside of the door frame. In places where the misaligned door frame causes spaces that are larger than two shims, use as many shims as necessary to fill the space between the inside face of the rough opening and the outside face of the door frame.

Check that the door frame is level using a 4-foot level across the top and vertically on each side. If a part of the door frame is not square, back the shims off on one side and tap them in on the other side to readjust the frame.

Attach the frame to the rough opening with 3-inch-long nails driven through the door frame, through the shims and into the face of the rough opening.