Things You'll Need
Electronic stud finder
Enough 2x4 boards to span the length of the new wall three times
Additional 2x4s for studs, enough to span the height of the wall every 16 inches, plus three additional studs at the end
3-inch wood screws
Building a load-bearing wall during new construction takes some engineering knowledge. Installing a non-load-bearing wall into an existing home just requires that it be put in straight and level. Still, it's important to follow standard procedures regarding the placement of studs and other issues so it doesn't look cockeyed or start falling down in a year. This plan assumes you're constructing a floor-to-ceiling wall that attaches to an adjacent wall on one side, stands alone on the other side, and doesn't need a doorway cut into it.
Snap a line on the ceiling where you want your wall to go. With your stud finder, locate and mark each ceiling joist along the span. Use your miter saw to cut a 2x4 to the length of the new wall and screw it to the ceiling alongside the snapped line, sinking two screws at each joist. This is your ceiling plate.
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Hang a plumb line from each end of the ceiling plate, on one side of it, to the floor, and mark the two points on the floor. Connect the marks with your snap line.
Cut two more 2x4s of the same length as the ceiling plate. One will be a top plate to screw against the ceiling plate, and the other will be a floor plate.
On each of the two new boards, measure 1 1/2 inches out from the side that will touch the existing wall, and mark a line there with your tri-square for your corner. Measure 16 inches over from that line and mark another line for the start of the next stud. Then mark another line 1 1/2 inches over from that one, to account for the thickness of the stud. Continue measuring across each of the boards, marking lines for studs every 16 inches. At the open end of the wall, mark for three studs in a row, pressed together.
Measure from the bottom of the ceiling plate to the floor, then subtract three inches from that number. That's the length you need for your studs. Cut enough 2x4s at that length to stand between each of the paired marks you've made on the floor plate and top plate.
Lay the top plate and floor plate on their edges, their marked sides facing each other, the boards far enough apart to fit the studs between them. Attach each stud to the floor and top plates by sinking two screws through the far side of the plate and into the ends of the stud. Frame out the whole wall.
Stand the wall up, with the floor plate along your floor line and the top plate butting up under the ceiling plate and even with it on all sides. Screw the top plate into the ceiling plate, sinking several screws upward on the flat spans of the top plate between each pair of studs.
Put a level on the outer edge of the new wall and move the bottom part of it out or back if necessary to get it level. Then screw the bottom plate onto the floor, sinking screws on the flat spans between the studs. Your wall is now ready for electricity installation if necessary, and drywalling.
Wear eye protection when using your miter saw and power drill.