How to Extend the Height of an 8-Foot Concrete Wall With a Wood-Framed Knee Wall

Measure the length of the knee wall. Cut the bottom plate and top plate to this dimension using a hand saw or circular saw.

Lay the bottom plate on top of the wall and mark the location of the bolts that protrude from the top of the wall. These bolts fasten the knee wall to the concrete wall.

Use a drill to bore holes through the bottom plate at the location of each bolt. Most wall anchor bolts are 1/2 inch in diameter, so use a 1-inch spade bit to drill the holes. This extra space will allow for easier placement of the knee wall.

Lay out the stud location on the bottom plate. Start at one end of the bottom plate and make a mark 1 1/2 inches from the end of the board. Use a square to draw a perpendicular line across the board at that point and then mark an X between the line and the end of the board.

Measure from the end of the board 16 3/4 inches and make a mark. Square a line across the board at this point as well and place the X on the same side of the line as the first one.

Continue from this second mark and make a mark every 16 inches until you reach the end of the wall. Square a line across the board at each mark and place an X on the same side as before. The last stud will be located at the opposite end of the wall and may not have a full 16 inches between it and the preceding stud.

Transfer these marks to the top plate.

Cut the wall studs using a hand or circular saw. Take the desired height of the wood-framed knee wall and subtract the thickness of the top and bottom plate from it, usually 3 inches, to determine the length of each stud.

Assemble the knee wall. Lay the top and bottom plates on edge a little farther apart than the length of the studs. The stud layout marks on each plate should be facing each other. Set the studs in place between the two plates. Each stud should line up on one of the X marks, with an edge lined up on the accompanying square line.

Nail through the plate and into the bottom of each stud. Use three nails at each stud. Nail all the bottom ends first and then nail the top ends. You can do this with a hammer and 16 penny framing nails, commonly referred to as coated sinkers.

Lift the knee wall into place and fasten it down by placing a large square foundation anchor washer and bolt on each anchor bolt and tightening them down with a wrench. Use a lot of force, as you don't want the wall to easily slide around. Have a helper lift the other end. Make sure the ladders rest solidly on the ground and against the wall.