What is a stair stringer?
A stair stringer is the angled structural board that runs beneath deck stair steps and supports the weight of the treads and anyone using the stairs.
The stair stringer is the angled board running beneath your deck stairs that carries the load of the treads and foot traffic. It connects the deck platform to the ground level and serves as the primary structural support for the entire stair assembly.
Stringers are most often cut from pressure-treated lumber, typically 2-by-10 or 2-by-12 material, though some builders use doubled stringers or solid steel for heavy-load applications. The stringer is notched or routed to receive the treads (the horizontal step boards), and sometimes the risers (the vertical boards between steps). The angles of the cuts depend on step height and run depth, which North Carolina building codes govern to ensure safe and consistent stair geometry.
Stringer count matters for stair width and safety. A single stringer can support stairs up to roughly 36 inches wide under normal residential loads, common for decks in the Greater Charlotte area. Wider stairs, or those serving high-traffic decks, need two or three stringers to spread the load evenly and prevent flex or bounce. Builders of elevated multi-level decks often size stringers conservatively to handle concentrated weight from multiple users on a single step. Local code inspectors check stringer spacing, fastening, and material grade during permit review, so proper stringer selection upfront prevents costly revisions.