Anatomy of a Staircase: Terminology, Parts & Building Codes

The Structural Backbone: Stringers and Carriages

Beneath the beautiful polished hardwood treads and decorative white risers lies the hidden structural engine of the staircase: the stringers (also known as stair carriages).

Stringers are heavy diagonal beams spanning from the lower floor framing to the upper floor header, supporting the entire dynamic weight of people and furniture traveling between levels. In residential construction, stringers are traditionally cut from dense 2x12 structural lumber or engineered laminated veneer lumber (LVL) planks.

A staircase is assembled from a coordinated assembly of horizontal, vertical, and structural support components. The table below outlines the primary anatomical parts of a staircase, their structural roles, and common construction materials.

Carpenters cut precise triangular notches along the top edge of the stringer to create horizontal beds for the treads and vertical backing for the risers. Residential building codes generally mandate a minimum of three parallel stringers for standard three-foot-wide stairs—one along each outer wall and a center stringer to prevent tread deflection and creaking.

Staircases can feature Cut Stringers (where the stepped profile is exposed to view along an open stair side) or Housed/Closed Stringers (where the treads and risers are routed into deep grooves inside a solid, unnotched stringer board and secured with hardwood wedges).

Properly sizing and anchoring stringers ensures the staircase remains solid, silent, and structurally sound for a century.

Treads, Risers, and the Architectural Nosing

The surface components that you see and step upon every day are the treads, risers, and nosings.

The Tread is the horizontal board that bears your physical footstep. Quality treads are crafted from dense 1-inch-thick kiln-dried hardwoods like red oak, white oak, or hard rock maple, which resist indentations from high heels and heavy shoes. In commercial or budget construction, treads are often constructed from heavy structural plywood designed to be covered in wall-to-wall carpeting.

The International Residential Code (IRC Section R311.7) enforces strict dimensional safety limits to prevent trip-and-fall injuries on residential staircases. Review the mandatory IRC building code benchmarks below.

The Riser is the vertical board that encloses the space between consecutive treads. In modern architecture, staircases can feature Closed Risers (traditional solid backing) or Open Risers (where the vertical space is open, creating a floating, minimalist modern aesthetic). Under IRC codes, open risers cannot allow a 4-inch sphere to pass through, requiring riser openings to remain under four inches.

The Nosing is the front rounded overhang of the tread that projects beyond the face of the riser below. Typically projecting between 3/4 inch and 1-1/4 inches, the nosing adds critical surface area for your foot during descent.

The underside of the nosing is often softened with a small decorative cove moulding, providing a classic finished look.

The Balustrade System: Newel Posts, Balusters, and Handrails

The protective barrier assembly installed along the open side of a staircase is known architecturally as the Balustrade. It comprises three interconnected components: newel posts, balusters, and handrails.

The Newel Post is the massive vertical anchor pillar positioned at the bottom, top, and directional turns of a staircase. Newel posts anchor deeply into the floor joists below, providing the rigid mechanical leverage required to keep the entire railing system from wobbling under lateral pressure.

Balusters—commonly referred to as spindles—are the smaller vertical uprights spaced closely together between the treads and the handrail. Balusters can be turned from decorative wood or forged from modern wrought iron with decorative knuckles, baskets, or scrolls.

The Handrail (or banister) is the continuous diagonal gripping bar that users grasp while climbing or descending. Building codes strictly mandate that handrails must possess a Graspable Profile—such as a round diameter between 1.25 and 2 inches, or a contoured Type-I architectural profile with finger-recess grooves.

Code prohibits bulky, flat 2x6 boards from being used as handrails because the human hand cannot securely wrap around them during a sudden slip.

The Golden Formula: The Rule of 25 for Comfort

Have you ever walked up a flight of stairs and felt instantly awkward, stumbling or taking uncomfortably high steps? That discomfort occurs because the carpenter violated the mathematical laws of stair ergonomics.

Human walking gait follows predictable biomechanical rhythms. When ascending a staircase, as the step height (rise) increases, the foot natural step depth (run) must proportionally decrease.

Centuries of architectural practice have established the famous Rule of 25 (also known as the Blondel formula): 2 Risers + 1 Tread must equal 24 to 25 inches (2R + T = 25).

For example, if a staircase features a comfortable 7-inch riser height, two risers equal 14 inches (2 x 7 = 14). Subtracting 14 from 25 yields an ideal tread depth of 11 inches. This 7x11 ratio is universally recognized by architects as the gold standard of effortless, ergonomic stair climbing.

Adhering to this mathematical harmony guarantees that ascending and descending your home staircase feels natural, rhythmic, and safe.

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