Cut the door header. To make the door header (the top of the door frame), cut two 2x4s to the same length as the width of the original opening and nail them securely together.
· You will need to add 1/2" of plywood between the 2x4's to get the right wall thickness of 3-1/2". This is the actual thickness of a 2x4.
Putting It Together
Insert the top plate. Nail the top plate through the ceiling into the ceiling joists or blocking using 12D nails.
Insert the sole plate. Nail the sole plate to the floor, driving the nails into the floor joists or blocking.
· Don't nail the sole plate to the floor between the jack stud locations because this portion of the plate will be removed before the door is installed.
· Use Tapcon screws (or other appropriate fastener) to insert the sole plate.