There are two different classes of stairs. The first class is a mill-made stair, which is usually fabricated in a mill shop and shipped to the job site as a kit, ready for assembly and installation. The second class, a carpenter-built stair, is just that — a stair built on site by a carpenter. This type of fabrication is less expensive and allows the stair to be covered with carpet. A carpenter-built stair can be dressed up with a hardwood or paint-grade skirt board. And simple wall-mounted railing is a popular option to complete either type of stair.