notchboard

A notchboard is a structural timber, typically 1.5 to 2 inches thick, that forms the sloped side of a staircase by receiving and supporting the cut ends of the treads and risers. The board itself is cut with a series of rectangular notches or recesses, spaced at equal intervals, into which the horizontal treads and vertical risers are fitted. This method of stair construction is sometimes called "cut string" or "housed" work, depending on how the boards are joined.

In a standard residential staircase, there are usually two notchboards, one on each side, though wider or commercial stairs may have a third center notchboard for additional support. The notches are typically routed or chiseled to a depth of 0.75 to 1 inch, creating a ledge that bears the full weight of foot traffic. The treads rest on the top shoulders of the notches, while riser boards slot in behind or between them.

Construction and Material Considerations

Notchboards are most often made from solid wood: pine, oak, or spruce are common in residential work, while laminated timbers or engineered lumber appear in commercial applications. The wood must be straight-grained and free of significant defects, since the notching process removes material and compromises the board's structural integrity. A poorly cut notch can create a weak point where the riser or tread might split under load. The thickness and width of the board are calculated based on the stair span and load requirements; a staircase spanning 12 feet might require a notchboard 10 to 12 inches wide.

The term "notchboard" is direct but somewhat informal in professional carpentry vocabulary. Architects and engineers more often use "stringboard," "stringer," or "string" interchangeably, though strictly speaking a stringer can refer to the complete assembled beam whether it is notched, housed, or closed (solid). The notching method is older and more visible than housed stringers, where treads and risers are let into grooves routed into a solid board, so notchboards are often seen in period or traditional staircases.

Common problems include notch shoulders that split or crack after years of deflection under load, particularly if the wood dries and shrinks unevenly. Loose or squeaking treads often result from notches that have worn or from fasteners that have worked free. Notchboards also expose the end grain and interior structure of the staircase, so they require paint or finish to match the rest of the carpentry; unfinished notchboards will absorb moisture and move dimensionally.