How to Add an Interior Doorway to a Load Bearing Wall

Draw the rough opening on the wall using a tape measure, pencil and straight edge. Its height should be the height of the door plus the width of the header plus an extra 3 inches. Its width should be the width of the door plus the width of the king studs plus 2 inches to account for the jamb and to allow for a small gap.

Cut through the drywall along the outline you drew with a drywall saw and remove the drywall from the opening. Push the saw through the drywall on the other side of the wall at the top two corners, then use the marks to draw a similar outline on the other side of the wall and cut away the drywall.

Make a mark on one of the studs bisecting the opening that is a distance from the floor equal to the height of the door plus the width of the header plus 2 inches. Place the bottom edge of a level on the mark, center the bubble so the level is horizontal, and use it as a reference for drawing similar marks on all the other studs that bisect the doorway.

Cut through all of the studs on the marks with a reciprocating saw and remove their lower portions. Pry them off the bottom plate of the wall, but leave the bottom plate in place.

Cut 2 lengths of 2-by-12-inch lumber that are slightly longer than the width of the opening with a circular saw. Use the saw to cut one piece of 1/2-inch plywood that is the same length as the boards you just cut and the same width. Nail the boards together with the plywood sandwiched in between them using 2.5-inch common nails.

Cut 4 pieces of 2-by 4-inch lumber the height of the door plus 2 inches. Nail them together in pairs to make two king studs to support the ends of the header.

Support the header in the opening on the two king studs, pushing it tightly against the top parts of the cut-off studs, and nail the ends of the header to the tops of the king studs. Nail the top parts of the cut-offs to the top edge of the header.

Frame the door opening by adding two more studs on either side a distance equal to the door width plus 2 inches. Plumb each stud with a level before you nail one end to the bottom plate of the wall and the other end to the header. Cut out the section of the bottom plate inside the doorway with a reciprocating saw when you are finished.

Install the door jamb starting with the top. Place cedar shims between it and the header, adjust the shims until the top jamb is exactly horizontal, then nail it in place with 2-inch finish nails. Repeat the procedure to install the side jambs, plumbing each with shims and a level and nailing it in place.

Finish off the opening by trimming around the jamb with door casing, which is trim specially designed for door openings. If you have made careful measurements throughout the procedure, the casing should cover the gap between the jamb and the remaining wall.