Stair Types & Components

Stair Types & Components

Quick Answer: Stairs move people between levels with treads (horizontal walking surfaces) and risers (vertical faces), supported by stringers (carriages). Landings change direction or break long flights. Handrails and guards protect users; newels, balusters, and nosing finish the assembly. Know straight, L, U, spiral, and winder layouts so you can read plans, order materials, and frame openings correctly.

Module 27110 (Basic Stair Layout) and Module 27405 (Finished Stairs) sit inside the Stair Systems domain on the Commercial Carpenter assessment (about 6 items). Items expect you to identify types and parts, then apply rise/run and stringer skills in the next sections. Start with vocabulary—if you misname a stringer as a joist or a guard as a handrail, every calculation and code answer that follows is at risk.

Why Stair Literacy Matters on the Job

A stair is a permanent vertical circulation system, not a decorative ladder. Wrong type for the footprint forces redesign. Missing a landing when code requires one fails inspection. Confusing handrail height with guard height produces unsafe, noncompliant work. Commercial carpenters also coordinate stair openings with floor framing (headers, trimmers), fire ratings, and accessibility notes—so the names on the plan must match the members you build.

Stair Types (Plan Geometry)

Stair type describes how the run occupies plan space and whether the path turns.

Straight-run stairs are the teaching default. One total rise, one total run, identical unit risers and treads end to end. Header and trimmer framing for the stairwell is rectangular and relatively simple.

L-shaped stairs place a landing at the corner so each flight stays a normal rectangular run. That is usually safer and easier to code-check than packing the turn with winders. On plans, look for a square or rectangular platform at the turn with handrails continuing or restarting per detail.

U-shaped stairs reverse direction 180°. Two flights share a common wall or open well; the intermediate landing may be a full-width platform. Multi-story commercial stairs often stack U-shaped flights in a rated stair shaft.

Spiral stairs use pie-shaped treads around a center support. They appear as secondary access (e.g., loft, mezzanine) more often than as the primary means of egress. Exam awareness: spirals have special dimensional limits and are not interchangeable with a straight residential stair under ordinary IRC assumptions.

Winder stairs turn the path with tapered treads instead of (or in addition to) a landing. Layout uses a walk line (typically offset from the handrail side) where tread depth is measured. Winders require careful marking so the narrow end never drops below code minimums at the walk line. Many jurisdictions prefer landings for primary stairs; treat winders as a specialized layout skill, not the default solution.

Scenario: A remodel must fit stairs into a 4' × 4' corner of a foyer. A straight-run will not fit the length available. An L-shaped stair with a landing in the corner usually solves geometry better than forcing a straight flight or an unplanned spiral. If the plan shows winders, verify walk-line tread depths before cutting stringers.

Primary Structural Components

Stringers (Carriages)

Stringers—also called carriages or stair horses—are the inclined structural members that support treads and risers. Common arrangements:

• Cut (open) stringers: Triangular notches cut for each tread and riser; treads sit on the horizontal cuts.
• Housed (closed) stringers: Grooves (housings) routed into the stringer face; treads and risers slide into the grooves and are wedged/glued—common on finish stairs.
• Center carriage: Extra stringer under wide stairs to reduce tread span.

Solid lumber (often 2×12 for cut residential stringers), LVL, or engineered stringers appear on commercial work. Outer stringers may be finish stringers with a rough carriage behind them. Always support stringers on solid framing at the top (header/trimmer or landing) and bottom (floor, pad, or kick plate)—not on finish flooring alone unless designed that way.

Treads and Risers

• Tread: The horizontal board or pan you step on. Depth (unit run) is measured as the horizontal distance from face of riser to face of riser (or nosing to nosing rules per code definition).
• Riser: The vertical board or face between consecutive treads. Closed risers fill the space; open-riser stairs omit solid risers where allowed.
• Nosing: The projection of the tread beyond the face of the riser below. Nosing improves foot placement and is limited/required by code ranges in many residential models.

Treads may be rough framing lumber later covered by finish treads, solid hardwood finish treads, or metal/concrete pans in commercial systems. Risers may be wood, drywall-faced, metal, or open.

Landings

A landing is a level platform at the top, bottom, or intermediate point of a stair. Functions:

1. Change of direction (L or U stairs)
2. Break long vertical travel into code-compliant flight lengths
3. Provide a rest and a safe door swing area (doors should not swing into the required landing width in a way that reduces clearances)
4. Support stringer ends and handrail transitions

Landings are framed like miniature floors: joists or solid blocking, subfloor or deck, and perimeter support. Commercial landings may be steel pan with concrete fill or precast.

Safety and Finish Components

Handrail vs guard: A handrail is for gripping while ascending/descending. A guard is a fall barrier at open sides. On open stairs they may combine (a guard with a graspable handrail on top or a separate handrail inside the guard). Exam trap: applying handrail height numbers to a balcony guard, or vice versa.

Balusters and openings: Infill must keep openings small enough that a child cannot pass through—model residential codes commonly use a 4-inch sphere test at guards (and often a different sphere size at certain stair openings). Use the figure in force for the job; the concept is maximum clear opening, not decorative preference.

Nosing: Beyond grip and edge definition, nosing dimensions affect effective tread depth. When you lay out stringers, nosing and finish tread thickness interact with drop calculations (next sections).

Reading Stairs on Drawings

Stair-related plan and section notes typically show:

• Number of risers and treads (note: number of treads is usually one less than number of risers in a simple flight between floors)
• Direction of travel arrows and "UP" / "DN"
• Stair width, landing sizes, and handrail locations
• Headroom notes and stairwell opening dimensions
• Material callouts (wood, steel pan, precast, etc.)

A section cut through the stair shows total rise, unit rise/run, headroom, and how stringers bear on floor framing. Match the section to the plan flight you are building—U-shaped stairs have multiple sections.

Commercial vs Residential Awareness

Residential teaching models often use wood cut stringers, wood treads/risers, and IRC-style dimensions. Commercial stair systems may use:

• Steel stringers with pan treads filled with concrete
• Prefabricated metal stairs set into shafts
• Rated enclosures, standpipes, and exit signage coordination
• Larger widths, different handrail extensions, and accessibility (ADA) criteria on accessible routes

Component names stay the same even when materials change. A pan tread is still a tread; a channel stringer is still a stringer.

Field Vocabulary Checklist

Before layout day, walk the crew through the sketch and name:

1. Top and bottom landings
2. Number of risers in each flight
3. Left/right stringers and any center carriage
4. Tread material and whether risers are open or closed
5. Handrail side(s), newel locations, guard requirements
6. Nosing type and finish thickness (affects stringer drop later)

Mastering types and components turns Module 27110 drawings into a parts list. The next section converts total floor-to-floor height into equal unit rises and runs that those stringers must carry.