To make this DIY project easy, use hardwood plywood along with pre-squared, pre-planed, dimensioned hardwood lumber, or S4S (“surfaced on four sides”) which can be found at better home centers. By using readily available stock lumber sizes, such as the 1x4 and 1x6, this project becomes more of a simple assembly job and less of a custom-cutting and fitting chore.
Start by measuring the length of each wall (Image 2). Draw a layout plan (Image 3) that divides the walls into panel sections of equal size. An accurate plan will also provide a template to use for buying and cutting the wood. The size of your room will influence the width of the panel sections, but because hardwood plywood comes in 4' x 8' sheets (48" x 96"), it is more economical in both materials and labor to create sections that make the best use of these dimensions.
If you have a large room, for example, the optimum proportion for each panel section would be 48" x 48", which includes the width and height of the (overlapping) vertical and horizontal rails. This allows you to use a full plywood sheet to cover two panel sections. If your room is small, or if its dimensions don’t accommodate equal 4-foot sections, reduce the width increments to 32 or 24 inches and still retain the 48-inch height (Image 4). The goal is to use full sheets wherever possible. If your room’s dimensions are slightly off, you can usually slightly adjust the width of each wall’s end panel sections.
When you measure the walls, use an electronic stud finder to locate and mark the position of the wall studs. It is to nail the vertical stiles to a stud so they'll be firmly anchored; however, because all of the stiles will be connected to the top and bottom rails, which span multiple studs and are well anchored, this is not required. In your layout, try to avoid placing any of the stiles over an electrical outlet.
If you are going to be painting the wainscot panels, it is best to prime them before installation.
Begin the installation at one corner of the longest wall. Measure up from the floor to the height you want your wainscot (ours is 35 inches), then use a level (or ideally, a laser lever) to extend this mark across the length of the wall. This line marks the top of the paneling and upper rail. The measurement includes a 1/4-inch gap at the bottom to allow for any variations in floor height.
Remove the room’s existing baseboard and discard it (Image 1). Also remove any electrical outlet covers, but leave the outlets in place.
Use a caulking gun to apply a continuous, serpentine bead of construction adhesive to the wall below the level line, extending the adhesive from top to bottom.
Place the first plywood sheet against the wall (Image 2), even with the level line, and tack it to the studs with two 1-1/2" finishing nails (Image 3). The next sheet should butt against the first and follow the level line. It is more important to maintain a level line along the top of the plywood, even if the joints do not butt tightly together; these joints will be covered by the vertical stiles.
Continue installing the plywood sheets to the end wall. Measure the last section to butt against the corner, and use a circular saw to cut it to fit. At electrical outlet locations, carefully measure and mark each panel before you install it, and use a razor knife or jigsaw to cut out the opening (Image 4). When all of the plywood sheets are up and level, fasten them to the wall studs with 1-1/4" finishing nails.
Install the horizontal top rail directly atop the top edge of the plywood. Use 2-1/2" finishing nails to fasten this rail through the plywood and wall and into the studs. If you have to connect two running pieces on a long wall, cut opposing 45-degree-angles on each piece to create a lap joint. Place a little wood glue on each cut end then overlap the pieces and fasten to the wall. For the corners, use a standard butt joint.
Cut all of the 1x4 stiles to size (ours measure 27-1/2"). Use a miter saw to ensure square (90 degree) cuts on the end of each board.
Measure and mark the stile layout; if it corresponds to the stud spacing in your walls, each stile will be directly over a stud. It is best to start in a corner and work out. For aesthetics, we choose to butt two pieces together in the corner (Image 1). Check each stile with a plumb level as you nail them in place with 2-1/2" finishing nails. Use a spacer board to ensure a uniform size in between each stile (Image 2). If any of the stiles do not fall on a stud, secure them by toe-nailing to the top rail using 1-1/4" finishing nails.
Measure and cut the baseboard. Where two boards meet, cut mating 45-degree miters on the end of each board to create an “invisible” lap joint. Add glue to the baseboard where it meets the bottom of each stile (Image 1). Use a pry bar or wood shims to raise the baseboard to meet the stiles. Secure the baseboards in place, nailing through the plywood and wall surface into the studs with 2-1/2" finishing nails. Adjust your pneumatic nailer to drive all nail heads slightly below the wood surface, or sink the nails with a hammer and nail set.
Measure and cut the cove molding to sit on top of the top rail (Image 2). As with the other horizontal rails, use miter cuts for intersections. Secure the cove molding using 1-1/4" finishing nails. To give your panels a more detailed look, you can also install cove molding completely around the inside of the stiles.
Measure and cut the shoe molding to run along the bottom of the baseboards to hide the gap where the paneling meets the floor.
Fill all nail holes with wood putty and allow it to dry. Lightly sand all of the wood surfaces with fine (#200) sandpaper and wipe away dust with a tack cloth the paint.
If you are staining the paneling, use a brush or rag to apply wood stain. Apply a full coat and allow it to penetrate for about 15 minutes, then wipe away excess stain. When dry, repeat with a second stain coat.
Allow the stain to dry overnight. Brush or spray on a light coat of polyurethane finish. Allow it to dry, then sand lightly. Use a tack cloth to wipe away dust, then apply a second coat of finish.