Remove the trim around the mudroom floor. Use a utility knife to cut through paint at the top of the trim piece. Use a pry bar to gently pry the wood from the wall.
Mark the wall where you want the top of the beadboard to hit. The panels of beadboard are usually 4-feet-by-8-feet so choosing 4 feet for your measurement makes cutting the beadboard simple, but you can make the beadboard area as tall as you'd like.
Make a chalkline or draw a line to mark the top of the beadboard around the entire room. Use a level to ensure it is even
Cut the beadboard panels based on your desired height on the wall using a table saw or circular saw. Cut the pieces so they reach the desired height while allowing 1/8 to 1/4 inch along the bottom edge for expansion.
Position the first piece of beadboard in a corner of the mudroom, leaving 1/8 inch between the edge and the corner for expansion. Nail the beadboard piece to the wall through the studs.
Work around the room nailing more panels of beadboard to the wall. Make cutouts for outlets and windows or doors as necessary when you reach those items on the wall.
Nail the baseboard back into place once you have all of the beadboard installed. Nail decorative trim or a cap rail along the top edge of the beadboard to give it a finished look. Use finishing nails for the best look on the wood.
Paint or stain the beadboard to finish the look. Use a high-glass paint to make the beadboard easier to clean off, as it is likely to get dirty in the mudroom area.