Last reviewed 16 Sept 2026 · 5 min read
Terminology
- Tread (going) — horizontal upper surface of a step; rise — vertical height between treads.
- Riser — vertical face of a step. Nosing — projecting edge of the tread.
- Flight — series of steps between landings. Landing — horizontal platform between flights.
- Waist — thickness of the inclined structural slab measured perpendicular to its soffit.
- Going of a flight — horizontal distance from the first to the last riser (number of treads × tread).
- Headroom — clear vertical height above the pitch line (commonly at least 2.1 m).
- Stringer — inclined beam supporting the steps along the edge.
Proportioning
| Building | Rise (mm) | Tread (mm) |
|---|---|---|
| Residential | 150–190 | 250–300 |
| Public buildings | 120–150 | 280–350 |
Comfort rules commonly used:
- = 550 to 700 mm (often 600–640 mm).
- ≈ 40 000 to 45 000 mm² (older rule of thumb).
- Width: about 0.9–1.0 m for residential stairs; wider for public buildings.
- Not more than about 12–15 risers in a single flight; pitch generally 25°–40°.
Types of stairs (by plan)
- Straight flight — single run.
- Quarter-turn — turns 90° at a landing.
- Dog-legged — two flights in opposite directions with a half-space landing and no well between them; economical in space.
- Open-well — like dog-legged but with a well (gap) between flights; comfortable and allows a lift in the well.
- Bifurcated — wide lower flight splitting into two.
- Spiral / helical — circular plan, used where space is very limited or for architectural effect.
- Geometrical — curved, without newel posts.
Structural classification
| Behaviour | How it spans | Main steel |
|---|---|---|
| Transversely spanning | Each step spans across the width between walls or a wall and a stringer beam (or cantilevers from a wall) | Across the width, in each step |
| Longitudinally spanning | The waist slab spans along the flight between supports (floor beam, landing beam or landing slab) | Along the slope |
| Cantilever steps | Steps project from a wall or central spine beam | Top of step |
| Folded plate (slabless) stairs | Tread and riser act as a folded plate | Following the profile |
IS 456 provisions
Effective span. For stairs spanning longitudinally, the effective span is the horizontal distance between centre lines of supports. Where the stair spans onto the edge of a landing slab that itself spans parallel to the risers, the effective span is the going of the stairs plus, at each end, half the width of the landing or 1 m, whichever is smaller.
Distribution of loading. In stairs with open wells, where spans partly cross at right angles, the load on areas common to both spans may be taken as one-half in each direction.
Depth of section. The depth is the minimum thickness perpendicular to the soffit of the staircase (the waist).
Deflection is checked with the ordinary slab span/effective depth ratios on the horizontal effective span.
Loads on a longitudinally spanning waist slab
Take all loads per square metre of horizontal plan area:
- Self-weight of waist: kN/m² (, , in m).
- Weight of steps (triangular portions): kN/m².
- Floor finish: 0.5–1.0 kN/m².
- Imposed load: 3.0 kN/m² for residential stairs, higher (up to 5.0 kN/m²) for public buildings where crowding is possible (IS 875 Part 2).
Design a 1 m wide strip as a simply supported slab on the horizontal effective span.
Design example
Floor-to-floor height 3.2 m; rise 160 mm, tread 250 mm; flight width 1.25 m; half-space landings 1.25 m wide at each end of the flight, spanning parallel to the risers. Imposed load 3 kN/m², finish 1 kN/m². M20, Fe 415, mild exposure. Design one flight.
1. Geometry. Each flight rises 1.6 m → 10 risers, 9 treads → going m.
2. Effective span. Going + half landing width at each end (0.625 m < 1 m): .
3. Trial waist. = 150 mm; mm (take 125 mm).
4. Loads (per m² of plan).
- Waist: kN/m²
- Steps: kN/m²
- Finish 1.00; imposed 3.00 → total 10.45 kN/m² → kN/m per metre width
5. Moment.
6. Steel.
mm²/m → 12 mm at 180 mm c/c (628 mm²) along the flight.
7. Distribution steel. mm² → 8 mm at 250 mm c/c.
8. Deflection. . Allowable: basic 20 × modification factor (≈1.45 for ≈ 0.5% and N/mm², from IS 456 Fig. 4) ≈ 29 > 28 ✔ (increase the waist to 160 mm if a stiffer stair is wanted).
9. Detailing. Main bars continue into the landings; at the re-entrant (inner) corner of the waist and landing, bars must not be continued round the corner, because the tension would pull them out through the cover. Provide separate bars crossing each other and anchored with on each side.