Stringer — What It Is, Where Used, and Replacement Guide

A stringer is the diagonal structural side board of a staircase that supports the treads and risers.

What It Is

Stringers are the backbone of a typical wood staircase. They carry the load of the steps and transfer that weight down to the floor framing or landing below.

On many residential stairs, the tread and riser geometry is cut into the top edge of the stringer, though some stairs use housed or boxed stringers with the steps set into routed pockets.

Types

Common types include cut stringers, housed stringers, wall stringers, open outer stringers, and center stringers used in some metal stair systems. Exterior deck stairs often use pressure-treated cut stringers sized for outdoor exposure.

Where It Is Used

Stringers are used on interior staircases, deck stairs, porch steps, basement stairs, and utility stairs. Most wood-framed stairs have at least two side stringers, and wider stairs may also have a center stringer.

How to Identify One

Look at the sloped side support of a stair. On open-sided stairs you may see the sawtooth profile under the treads, while on enclosed stairs the stringer may be hidden behind finish materials.

Replacement

Replacement is needed when a stringer cracks, rots, splits at the notches, or was cut incorrectly and leaves the stairs bouncy or uneven. Because the stringer is structural, replacement usually means rebuilding a major part of the stair assembly.