Walk to the area in the room where you want the half wall. Slide a stud finder along the floor and adjoining wall to locate the floor joists and wall stud. Mark their locations for future reference.
Measure from a side wall into the room to the point where you want the half wall to stop. Make note of this measurement. Measure a 2-by-4 board to match the wall length and mark it. Place a square on the board and draw a straight line across the 2-by-4 at the mark.
Cut the board with a circular saw along the line. This board will serve as a template to make another one the same length. Place the board on top of a second 2-by-4 and even it up on one end. Mark the other end and cut the second board along the mark. Once cut to length, these boards are your top and bottom plates for you wall frame.
Measure in from the right side of one of the boards to a distance of 16 inches and draw a straight line at that mark. Repeat by measuring from the drawn line out another 16 inches. Continue until you have marked the board every 16 inches along the length. The marks indicate where you should place the right side of each wood stud in order to maintain equal spacing. If there is less than 16 inches between the last mark drawn and the end of the board, you will still need to attach a stud at the end of the board for support, even though it is less than 16 inches away from the other studs.
Place the second board on its side right next to the one that is marked for studs. Align the boards and transfer the lines to the second board. Place the square across both boards and line it up so that it is square with the boards and on one of the marks. Draw the line from the first board to the second. Repeat this process for each line.
Measure up from the floor to a height of 3 feet so that you can get an idea of height. Move the tape higher if after looking at the 3 foot height you decide that you prefer the wall be taller. Half walls are usually anywhere from 3 to 4 feet high. The exact height is your choice. After settling on a wall height, subtract the thickness of the two boards you have been working with so far, which are the top and bottom plates of the wall. The thickness of a 2-by-4 is usually 1-1/2 inches, but it is best to measure it yourself to double check. This measurement is used for the stud beams.
Cut studs to equal the adjusted measurement determined at the end of Step 6. Measure one board to this length and cut it with a circular saw. Let this board be the template for all the other boards to ensure they are the same. Place the board on the other 2-by-4 boards to mark the length, then cut them out as well.
Attach the boards to the bottom plate. Place the studs so that the right side of the boards is on the marks you made. Drill 3-inch screws through the bottom plate and into the studs. Use two screws for each board so that the boards cannot twist. Once you attach the studs to the bottom plate, repeat the process with the top plate. As you attach the top plate, check each stud with the square to ensure they are at a right angle to the plates.
Place the wall frame where you marked the wall and floor joists. Drill 4-inch screws through the floor and wall, and into the joists and stud. For a more secure wall, consider attaching bolts on the floor instead of screws. Drill holes to accommodate the bolts and tighten them down with a socket wrench.
Measure the wall along the side and transfer the measurement to a piece of drywall. Score the board with a utility knife. Place the drywall along the edge of a flat surface, such as a table, so that the score is along the edge. Press down to snap off the excess. Let the cut piece of drywall be the template for a second piece, since you need one for each side of the wall. Depending on the length of the wall, you might need more than one piece of drywall to cover a side.
Place the drywall against the wall and attach it. Drill drywall screws through the panel and into the studs. Repeat this process on the other side of the wall.
Measure the end of the wall. Include the drywall edges with the thickness. Cut out a piece of drywall to this dimension. Attach it to the end of the wall, covering up the wood and the edges of the side wall drywall.
Measure the top of the wall. Include the drywall in the measurement for the thickness as well as the drywall on the end as part of the length. Cut out a piece, place it on top of the wall, and attach it with drywall screws.
Place metal corner wall strips along the corners. Drill screws through the holes in the strips and into the walls.
Spread drywall mud along the seams between any sheets of drywall, over screw heads and over corner strips. Spread the mud with a 4 inch taping knife. Place drywall tape over any seams while the mud is still wet, and then spread another layer over the tape. Let it dry overnight.
Sand the mud surface, then spread on additional mud with a 6-inch taping knife. Taper the mud out as you move out from the tape, screw heads or metal strips. Let it dry over night, then sand smooth.
Paint the wall with paintbrushes and paint rollers in long even strokes. Select a paint that matches the rest of the room walls. It is best if you put down a drop cloth to protect the floor.