Install a partition wall in a finished room by framing the stud wall flat on the floor, standing it up, and adding the drywall. Finish the wall to match the two new rooms it creates. Prior to beginning this construction project, check with local building authorities to determine if they require a building permit.
Prior to building the new wall, remove the carpet and padding from where you plan to place it. Cut the floor trim to make room for the wall.
Measure the floor and ceiling plates to the length of the wall. Mark the stud locations at 16-inch centers. If the new wall has a door, mark the location, and cut the opening in the bottom plate. Use 16-penny nails to attach the studs to the plates.
Move the new framing into place, and use a carpenter's level to ensure it is vertical. Nail the wall into the floor, ceiling and existing walls.
Attach drywall to the frame, leaving the door open. Use tape and drywall mud to cover any seams and nail or screw heads. Apply drywall texture to match the existing rooms. Once the texture is dry, prime and paint the wall. Add floor trim, and install the door to complete the project.