When measuring for wainscot material, buy 15 percent more than you think you'll need. When you are measuring for material, decide in advance if you want to run a baseboard material along the slope of the stairs or if you want to run the paneling down to the risers and treads of each individual stair. For the baseboard, as well as any other decorative trim capping the wainscot, order by the linear foot. For the paneling itself, order by the square foot or, in the case of panels, by the panel based upon your linear measurements.
Cutting each individual panel down to size to fit around the risers and treads of the stairs is a time-consuming process that also requires heavy use of tools throughout. This is especially true if you are using plank panels as opposed to larger panels, as each individual plank board needs to be cut to fit. Adding a baseboard section to the bottom portion of the wainscoting where it runs along the slope of the stairs means you can notch out that single board to fit around the steps (or more than one if a longer length is required), install it, then simply cut the wainscoting to the top slope of the baseboard, which offers a long, straight reveal as opposed to notching the individual panels.
Installation depends on the type of material you are working with, but as a general rule wainscoting is installed by gluing or adhering the material to the face of the wall. Nails can be used to further mount wood-type wainscoting. For best results, dry-lay things out on the floor to get an estimate of per-panel size and then use a level and pencil to lay things out on the wall, giving you points of reference to refer to during your installation. This keeps you working in smaller sections to keep things plumb and level bit by bit, rather than working on a large portion only to find out it’s slightly out of plumb from three planks back. Install the baseboard trim first if you are using it; otherwise, install panel by panel.
Regardless if you are cutting baseboard down to fit or each individual panel, use an angle finder in advance to determine that your stairs are all set at a 90-degree angle. Set the angle finder to one stair, then check them all to see if they match up. Use this gauge when marking the baseboard for stair notches, or for marking individual panels. Remember that the wainscots need to have at least 1/8 inch of a gap at the area where they meet the stairs to allow for expansion during warmer months. This joint is caulked after installation. If you're nailing the panels, use a brad nailer to keep the impression holes small, then fill them with wood putty and sand and stain or paint them. Use a stud finder beforehand and mark the studs' location with a level within your area of installation to guide your nailing.