---
title: "Vertical circulation elements; RCC dog-legged stair"
subject: "Building Technology"
chapter: 5
key: "semester_6/building_technology:stair-circulation-068ba"
source: https://www.bctengineer.com/q/semester_6/building_technology/stair-circulation-068ba
site: BCT Engineering
---

# Vertical circulation elements; RCC dog-legged stair

Building Technology · Chapter 5: Stair, lifts and escalators

- Asked in: 2068 Baisakh (old course), 2+6 marks
- Video: [5.1 Introduction to Staircases | CE601 |](https://www.youtube.com/watch?v=IYjVi-f8LhE) — RGPV Official
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/stair-circulation-068ba
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-5

## Question

What are different elements for vertical circulation in a building? Design a RCC doglegged staircase for a residential building in a room of 4.5m × 2.3m and floor height of 3m. Assume necessary data. Give neat sketches of the plan and section.

## Short answer

Elements: stair, ramp, lift, escalator, ladder. For 3 m height in 4.5 m × 2.3 m room: 20 risers of 150 mm, treads 250 mm. Two flights of 10 risers each, 9 treads; flight width 1.1 m, going 2.25 m, waist slab 175 mm.

## Answer

#### Elements for vertical circulation
1. **Stair:** the most common, with flights and landings.
2. **Ramp:** a sloping surface (about 1:12) for wheelchairs and trolleys.
3. **Lift (elevator):** a mechanical car in a shaft that carries persons or goods.
4. **Escalator:** a moving stair for heavy traffic.
5. **Ladder:** steep rung access to lofts and roofs.
6. **Paternoster, chute and fire escape:** other special devices.

#### Design of RCC dog-legged stair
Room 4.5 m x 2.3 m, floor height 3.0 m.

#### Given data and assumptions
- Stairwell (internal): 4.5 m x 2.3 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
- Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.1$ m.

#### Design
1. **Number of risers** $= H/R = 3/0.15 = 20$, adopt **20 risers**; exact riser $= 3/20 = 150$ mm.
2. **Flights:** a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the landing or upper floor acts as the last tread).
3. **Going of one flight** $= 9 \times 0.25 = 2.25$ m.
4. **Width:** two flights of 1.1 m side by side need $2b = 2.2$ m; the remaining $W - 2b = 2.3 - 2.2 = 0.1$ m is the gap between the flights.
5. **Landing:** a half-space landing 1.1 m x 2.3 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. **Length check:** going + landing $= 2.25 + 1.1 = 3.35$ m $\le 4.5$ m, so it fits; the spare 1.15 m is kept as entry/exit space.
7. **Check:** $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. **Waist slab:** effective span about 3.35 m, so depth $\approx$ span/20 $= 168$ mm; adopt a 175 mm thick waist slab (reinforcement to be designed separately). Provide a handrail 0.9 m high, 20-25 mm nosing and a non-slip finish.

#### Plan and section
```text
 +------------------------+---------+
 | FLIGHT 2  <<<<<<  UP   |         |
 | 9 treads               | LANDING |
 +------------------------+ (b x W) |
 | FLIGHT 1  >>>>>>  UP   |         |
 | 9 treads               |         |
 +------------------------+---------+
 <-------- going -------> <-- b -->
 (entry at left end of flight 1; arrows point up the stair)
```
```text
 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00
```

#### Summary
| Item | Adopted |
|---|---|
| Riser | 150 mm (20 nos.) |
| Tread | 250 mm |
| Flights | 2 flights x 10 risers |
| Width of flight | 1.1 m |
| Waist slab | 175 mm |

**Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.1 m.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which is a vertical circulation element?
   A. Corridor
   B. Lift
   C. Partition wall
   D. Foyer
   Answer: B. Stairs, ramps, lifts, escalators, ladders and chutes are vertical circulation. (Key point: Elements)

2. A dog-legged stair for H = 3 m, R = 150 mm has
   A. Two flights of 10 risers
   B. One flight of 20
   C. Three flights
   D. Two flights of 12
   Answer: A. 20 risers split equally into two flights of 10. (Key point: Flights)

3. Room width 2.3 m, flights 1.1 m wide leave
   A. 0.1 m
   B. 0.2 m
   C. 1.2 m
   D. 0
   Answer: A. 2.3 - 2.2 = 0.1 m. (Key point: Well gap)

4. Span 3.35 m, depth about span/20 is
   A. 168 mm, adopt 175 mm
   B. 335 mm
   C. 50 mm
   D. 1000 mm
   Answer: A. 3350/20 = 168 mm; adopt 175 mm. (Key point: Waist slab)

## Related in Building Technology

- [Dog-legged RCC stair design for 3 m floor height](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-dog-3m-assume) — Building Technology, chapter 5, asked 3×
- [RCC dog-legged stair for office building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arcc-stair-office-building) — Building Technology, chapter 5
- [Dog-legged RCC stair, 4.6 m by 2.6 m](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adog-legged-stair-residential-4p6m) — Building Technology, chapter 5, asked 3×
- [Dog-legged stair, 4.5 m by 3.0 m lobby](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adog-legged-stair-lobby-4p5m) — Building Technology, chapter 5
- [Dog-legged stair design with elevators and ramp](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-078c) — Building Technology, chapter 5
- [Dog-legged stair, 5.0 m by 4.0 m](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adog-legged-stair-public-5m) — Building Technology, chapter 5