How to Build a Knee Wall for a Raised Countertop

Measure from a wall, cabinet or other structure to determine the wall placement. Mark the length of the knee wall as well, either drawing the wall location and length on the floor or spreading tape to indicate. As a rule of thumb, allow a minimum of 42 inches around a bar or island for walkway clearance. Provide at least 24 inches of room per person for seating if the countertop will serve as a bar.

Measure and cut two pieces of 2-inch-thick lumber to the length of the wall desired less any countertop overhang. Most countertops will allow up to 12 inches overhang in any direction without additional support. However, for strength and durability or if the counter ends at a wall, for instance, you may choose to support the overhang, lessen or eliminate it.

For a 5-foot-long bar, for example, the knee wall may measure 40 inches in length with 10-inch overhangs on either end. Keep in mind that 10 to 12 inches is needed to allow knee room when sitting at the counter.

Lay the two boards, cut to the proper length, side by side. Measure down the length, making a mark at 1 1/2 inches, 12 inches and every 12 inches thereafter until the end. Make an additional mark exactly 1 1/2 inches away from the board end, regardless of the distance between the last two marks. Draw through both boards -- called the top and bottom wall plates -- with one stroke along a carpenter's square. These marks indicate the middle of each stud -- the vertical framing members -- in the knee wall.

Count the number of stud marks. Cut one 2-inch-thick board per mark to frame the wall. Use the countertop height desired minus 3 inches, which is the combined thickness of the two plates, and the thickness of the countertop material and plywood underlayment if used. Base cabinet counters typically measure about 36 inches high while bars are generally 40 to 42 inches in height. Since this is a custom installation, feel free to adjust it to suit your height.

For a 40-inch-high breakfast bar, as an example, topped with only a 3/4-inch-thick granite slab, subtract 3 3/4 inches from 40 inches. Cut each stud to 36 1/4 inches. For a tile surface, however, with a 3/4-inch-thick layer of plywood substrate, the studs may measure 40 inches minus 4 inches for a total of 36 inches.

Lay a plate on the floor on its 2-inch edge. Align a stud, flush with the end of the plate and also resting on its 2-inch edge. Nail through the plate into the stud end with two 16d nails. Continue down the length of the plate similarly. Attach the opposite plate to the free ends of the studs. When complete, the wall will measure the finished countertop height less the countertop material thickness by the width of board used. Thus, a wall made from 2-by-6-inch boards will yield a wall 5 1/2 inches deep by the height and length as constructed.

Erect the wall, aligning it with the floor marks. Hold a level up against the wall to ensure a plumb installation. Place the level on top of the wall as well to ensure the wall itself is level. If it isn't, add thin wood shims under the wall to obtain. Nail through the bottom wall plate into the floor beneath to anchor it in place. Add nails, driven through the last stud into the adjoining wall, wherever applicable.

Attach a sheet of 3/4-inch plywood. If required for the countertop material desired, cut to the appropriate length and width. Spread construction adhesive across the top plate. Set the plywood in place and nail to the plate. Top with the countertop material. Incorporate L-shaped brackets or other bracing if desired, following the product instructions. Sheath the wall with your choice of material, from drywall to wood sheeting, to complete.