A stair stringer is the structural backbone of a staircase. It supports the treads (the part you step on) and risers (the vertical space between treads), holding the entire stair assembly in place. Whether residential or commercial, interior or exterior, stringers ensure stability, safety, and load-bearing strength.

Key Aspects of Stair Stringers:

Function:
Provides structural support, alignment, and durability for the staircase. It ensures the steps are secure and can withstand daily use.

Placement:
Typically located on each side of the stairs, but can also appear as a central support (mono stringer) or as multiple supports depending on design and load needs.

Materials:
Wood (e.g., pressure-treated 2×12): Common in residential stairs.
Steel or Aluminum: Ideal for modern, industrial, or commercial applications.
Concrete or Composite: Used in large-scale or exterior projects requiring additional durability.

Types of Stair Stringers:

Closed (Housed) Stringers:
Treads and risers are set into routed slots, concealing step edges for a clean, traditional look.

Open (Cut/Sawtooth) Stringers:
Expose the profile of each step, offering a decorative and classic appearance.

Mono (Central) Stringers:
One central support beneath the stair treads creates a sleek, floating effect often seen in modern architecture.

Double Stringers:
Two stringers — one on each side — offer symmetrical support and are commonly used in commercial stairs.

Cantilevered Stringers:
Hidden within a wall, these create a dramatic, open “floating stair” look with minimal visible support.

Building Code Compliance:

To ensure safety and structural integrity, stair stringers must follow local and national building codes. For instance, the International Residential Code (IRC) typically requires:

Maximum riser height: 7 ¾ inches
Minimum tread depth: 10 inches
Uniformity: Variations must be minimal to prevent trip hazards

Summary:

Stair stringers are essential to both the form and function of a staircase. Whether crafted from wood, steel, or aluminum, and whether traditional or modern in style, they form the solid foundation that supports safe, long-lasting, and visually striking stairs.