InstaBidsTypes of stairs?
Types of stairs include straight runs, landing turns, winders, spirals and curves; choose around the opening and support, using SMA’s glossary (read 2026-11-09). For tight openings, compare the 2024 IRC’s 36-inch ordinary clear width, 10-inch tread depth and 26-inch spiral clear width before choosing a layout. (source: Stairbuilders and Manufacturers Association)
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Stair layouts and support choices
| Options | What the name describes | What to compare on the drawing |
|---|---|---|
| Straight | A straight flight runs without a turn; closed stringers describe the cited box-stair variant. | Use when the plan calls for one straight flight; identify whether its stringers enclose the treads. |
| L-shaped | Two flights join at a quarter-space landing. | Use a landing to change direction between the flights. |
| U-shaped | Flights join with landings in a U-shaped plan. | Use flights and landings arranged in a U-shaped plan. |
| Winder | Nonparallel tread edges create the turning steps. | Compare turning treads with a landing-based turn on a dimensioned plan. |
| Spiral | Uniform winders radiate around a minimum-diameter circle. | Compare its circular plan and separate clear-width and headroom provisions. |
| Curved | The plan contains an arc, combined radii or an ellipse. | Identify the radius, combined radii or ellipse in the proposed plan. |
| Floating | The SMA definition describes support at the floor systems, without wall support. | Choose the support arrangement separately from the plan shape and riser openings. |
Dimensions that can change the stair layout
| Options | Model-code dimensions | Measurement limits |
|---|---|---|
| Ordinary stair | 36 inches clear width above permitted handrail height; 10-inch minimum tread depth; 6 feet 8 inches minimum headroom, with stated exceptions. | Width is not total footprint; below-handrail dimensions differ. Spiral stairs have separate provisions. |
| Winder turn | 10-inch minimum tread depth at the walkline; 6-inch minimum at any point within clear width. | Measure turning treads at the specified locations; the section gives spiral stairs a separate exception. |
| Spiral stair | 26 inches minimum clear width at and below handrails; 6 feet 6 inches minimum headroom. | Clear width is not the total diameter or the floor-opening size. |
Keep interior layouts separate from exterior components
Interior and exterior are different scopes
HUD’s undated multifamily planning table gives exterior wood stair treads 15 years in row 3.3.2.7.2; that exterior-component estimate does not rank interior stair layouts by climate.
What type of stairs are there?
Stair choices include straight, L-shaped, U-shaped, winder, spiral and curved layouts; floating describes how a stair is supported. For ordinary stairs, the 2024 IRC specifies 36 inches of clear width above handrail height. SMA’s glossary distinguishes quarter-space landings from nonparallel winder treads.
Start with the route between floors: an L-shaped stair joins flights at a quarter-space landing, while a U-shaped plan uses one or more landings. A floating support arrangement can accompany a plan shape; it does not identify the turn by itself.
HUD’s undated multifamily table assigns interior stairs 50 years for capital-needs planning in row 3.7.2.4.4. The common-area interior-stair row also uses 50 years; neither row ranks these layouts by service life.
Source: Glossary: stair layouts and structural terms, read 2026-11-09
Source: 2024 IRC, Chapter 3: R318.7 stairways, read 2026-11-09
Source: CNA e-Tool Estimated Useful Life Table, read 2026-11-09
Which type of stairs take less space?
Spiral stairs allow a different clear-width limit: the 2024 IRC specifies 26 inches at and below handrails, while ordinary stairs require 36 inches above handrail height. Those measurements use different locations and do not establish total footprint; compare a dimensioned plan of the opening, landings and walking path.
Winders turn with nonparallel tread edges, while L-shaped stairs turn at a landing. For winders, the model code still calls for 10 inches of tread depth at the walkline and 6 inches within the clear width, so a turning tread is not permission to omit dimensional checks.
Source: Glossary: stair layouts and structural terms, read 2026-11-09
Source: 2024 IRC, Chapter 3: R318.7 stairways, read 2026-11-09
What is a spiral staircase?
A spiral staircase has a closed circular plan with uniform winders radiating from a minimum-diameter circle, according to SMA. The 2024 IRC treats spiral geometry separately: R318.7.11.1 calls for at least 26 inches of clear width at and below handrails and headroom of at least 6 feet 6 inches.
Ask the drawing to show the stair’s total diameter and floor opening separately from its clear walking width. The 26-inch rule measures the walking space at and below the handrails; it is not the outside diameter of a staircase or a recommended opening size.
Source: Glossary: stair layouts and structural terms, read 2026-11-09
Source: 2024 IRC, Chapter 3: R318.7 stairways, read 2026-11-09
What are winder stairs?
Winder stairs turn with treads whose edges are nonparallel, rather than making the turn on a flat landing. The 2024 IRC’s R318.7.5.2.1 calls for 10 inches of depth at the walkline and at least 6 inches at any point within the clear stair width; spiral stairs have a separate exception.
Compare the turning steps on a plan that marks the walkline. A proposal that names only an L-shaped stair can leave the turn unclear: SMA defines its L-shaped stair using a quarter-space landing, whereas a winder is a tread with nonparallel edges.
Source: Glossary: stair layouts and structural terms, read 2026-11-09
Source: 2024 IRC, Chapter 3: R318.7 stairways, read 2026-11-09
What are floating stairs?
Floating stairs, in SMA’s definition, have no wall support and attach only to floor systems at the top and bottom. Open risers are a separate detail: the 2024 IRC restricts passage of a 4-inch sphere through openings more than 30 inches above the floor or grade below, with a spiral-stair exception.
Ask the proposal to name the load-support arrangement and the riser-opening detail separately. The structural description does not settle the opening size. Preserve the code’s height condition and exception when discussing an open-riser look with a bidder; an image alone does not establish that geometry.
Source: Glossary: stair layouts and structural terms, read 2026-11-09
Source: 2024 IRC, Chapter 3: R318.7 stairways, read 2026-11-09
What a stair proposal should show
- Name the plan: straight, L-shaped, U-shaped, winder, spiral or curved; identify floating support separately.
- Draw the quarter-space landing for an L-shaped stair, or identify the nonparallel turning treads if winders are proposed.
- Show clear width above and below handrail height, not only the outside opening.
- Dimension ordinary tread depth against the 2024 IRC’s 10-inch minimum where that model-code provision applies.
- Mark the winder walkline and the 10-inch and 6-inch tread measurements in the turn.
- For a spiral stair, show the floor opening and diameter separately from its 26-inch clear-width requirement.
- Show the headroom measurement: ordinary and spiral model-code provisions differ.
- For floating stairs, name the floor-system supports and dimension any open-riser openings with their height condition and exception.
Sources
- Glossary: stair layouts and structural terms — Stairbuilders and Manufacturers Association; undated; read 2026-11-09.
- 2024 IRC, Chapter 3: R318.7 stairways — International Code Council; 2024 edition; read 2026-11-09.
- CNA e-Tool Estimated Useful Life Table — U.S. Department of Housing and Urban Development; undated; read 2026-11-09.
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