Installing a doorway into a stud wall is a do-it-yourself job that will take the better part of an afternoon and requires a little specialized knowledge, but anyone with the right tools can accomplish it. If it simply the framed stud wall you're working with, installing a doorway should be fairly straightforward. However, if you must cut through and existing finished wall to put in the doorway, the process may be complicated by the presence of wiring or piping. Assuming you're framing the doorway from scratch, follow this simple how-to for a quick, effective method.
Step 1: Measure the Rough Opening
Measure the width of the door with the tape measure. Directly above where the door will hang, mark the widthwise center point on the ceiling. On either side of that center point make another mark on the ceiling half the door's width from it. The 2 new resulting ceiling marks represent the inside edges of the trimmer or jack studs immediately bordering a door. Mark the center point and outer points on the bottom plate as well with the door in rough position.
Step 2: Mark King Stud Position
The king studs are those that run from bottom to top plate. The trimmer studs only run from the floor to the top of the door. To indicate the position of the king studs, measure 1½ inches out from both of the outer marks on the ceiling. These 2 marks represent the inner edges of the king studs. Don't forget to mark the inside edges of the king studs on the bottom plate too.
Step 3: Install King Studs
Cut to length the 2 king studs and nail them in place to the bottom and top plates. Use the outer marks on the ceiling and bottom plate as your guide. Use the level to check the plum of both studs before affixing them permanently.
Step 4: Install Trimmer Studs
Measure and cut the 2 trimmer studs to the same height as the door itself. Join the studs at their broad sides by attaching one each to the inside of both king studs from the bottom plate up. Use 3-inch nails driven every 10 to 12 inches in a zigzag pattern.
Step 5: Cut and Mount the Header
Next, measure the horizontal distance between the inside edges of the 2 king studs. Cut a piece of 2x4 to this length and lay it on its broad side atop the trimmer studs. This piece, the header, should fit snugly between the king studs while resting fully on the top edges of the trimmer studs. Nail it into place using 3-inch nails.
Step 6: Install the Cripple Studs
The cripple studs are positioned like any other stud but are installed between the header of a doorway and the top plate. They add support and should be spaced identically to the other studs, most commonly every 16 inches on center. You'll generally need only 2 or three cripples. Cut them to size, measure and mark their position and nail them into place.
Step 7: Cut Out Bottom Plate
With the handsaw, cut out the section of the bottom plate between the inside edges of the trimmer studs. Once cut, remove the piece. Now you can install the frame of the door followed by the door itself.