Floor Plate Installation
When a floor is uneven, the best way to frame a new wall is to set the floor and ceiling plates first. Use a chalk line on the floor to indicate wall placement, and cut a 2-by-4 pressure treated plate to fit. Attach the board, which serves as the floor plate, with powder fasteners or cut nails every 32 in.
Ceiling Plate Installation
A laser level comes in handy so you can align the ceiling plate directly over the floor plate. Before attaching the ceiling plate, however, lay it on the floor beside the installed floor plate; use a measuring tape and a straightedge to make pencil marks on both to indicate the placement of wall studs. Standard studs are 16 inches apart, measured from the center of one stud to the center of the next stud. Attach the ceiling plate using the same nailing pattern used for the floor plate. The ceiling plate will attach either to the ceiling joists it crosses or to the blocking.
Installing Wall Studs
Once the floor and ceiling plates are in place, installing the wall studs is relatively simple. The caveat here is that you must measure the distance between the plates for every stud and cut each one to fit. Because the floor is uneven, the studs will not all be the same length. Cut the studs on the outside edge of your measurement line to ensure that they fit snugly between the plates before attaching them with 16d nails at the top and bottom. The standard nailing pattern for attaching wall studs is to insert two nails, evenly spaced, at a 45-degree angle on one side of the stud and a single nail, in the middle, on the other side of the stud. Nailing at an angle is called “toenailing” and the same pattern is used to attach the top and the bottom of each stud.