--- title: "Open-well stair, 5.5 m by 3.5 m" subject: "Building Technology" chapter: 5 key: "semester_6/building_technology:open-well-stair-public-5p5m" source: https://www.bctengineer.com/q/semester_6/building_technology/open-well-stair-public-5p5m site: BCT Engineering --- # Open-well stair, 5.5 m by 3.5 m Building Technology · Chapter 5: Stair, lifts and escalators - Asked in: 2062 Poush (old course) - Video: [Design of open well stair](https://www.youtube.com/watch?v=vJVsVchCz8o) — WIT Solapur - Professional Learning Community - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/open-well-stair-public-5p5m - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-5 ## Question What are the functional requirements of good staircase? Mention the types of staircase (by shape) with neat sketches. Design an open-well staircase for a public building in a room of 5.5m×3.5m and floor height 3.6m. Give neat and clean sketch of plan, sectional elevation and necessary details. ## Short answer Designed open-well stair: floor height 3.6m, 24 risers at 150mm, tread 300mm, flight width 1.5m, going 3.3m, open well 0.5m, landing 1.5m×3.5m. ## Answer #### Functional requirements of a good staircase 1. **Location:** easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not reached through rooms. 2. **Width:** residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass. 3. **Easy and safe ascent:** riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal. 4. **Pitch:** between 25 and 40 degrees. 5. **Number of steps per flight:** not more than 12 and not less than 3. 6. **Landings:** provided at turns and between flights, with width not less than the stair width. 7. **Headroom:** at least 2.0-2.2 m clear above every step. 8. **Strength and fire resistance:** strong enough for the live load; fire-resistant material, with a separate fire-escape stair in tall buildings. 9. **Handrails and balustrades:** about 0.9 m high, strong and safe for children. 10. **Surface:** non-slip treads, good lighting and ventilation, durable and pleasing in appearance. #### Types of staircase by shape | Type | Description | |---|---| | Straight (single flight) | One continuous flight between two floors, no turn | | Quarter-turn | Direction changes by 90 degrees at a quarter landing | | Dog-legged | Two flights in opposite directions with a half-space landing, no well between flights | | Open-newel / open-well | Two or more flights with a clear well between them | | Half-turn (two-flight) | Turn of 180 degrees, either dog-legged or open-well | | Three-quarter turn | Three flights turning through 270 degrees around a well | | Bifurcated (branching) | One wide flight splits into two narrower flights at a landing | | Geometrical | Curved flights (circular or elliptical in plan) around an open well, without newel posts | | Circular / spiral (helical) | Wedge-shaped steps (winders) radiating from a central post; used where space is limited | ```text Straight Quarter turn Dog-legged Open well Spiral | | |__ |>>|<<| |>>| | ( o ) | | | |_ |__|__| |__|<<| | | |__| ``` #### Design of open-well staircase Room 5.5 m x 3.5 m, floor height 3.6 m, public building. #### Given data and assumptions - Stairwell (internal): 5.5 m x 3.5 m; floor-to-floor height $H = 3.6$ m; stair for a public building, RCC. - Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.5$ m. #### Design 1. **Number of risers** $= H/R = 3.6/0.15 = 24$, adopt **24 risers**; exact riser $= 3.6/24 = 150$ mm. 2. **Flights:** open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 12 risers and 11 treads. 3. **Going of one flight** $= 11 \times 0.3 = 3.3$ m. 4. **Open well:** $W - 2b = 3.5 - 3 = 0.5$ m wide open well is left between the flights and protected by a balustrade. 5. **Landing:** 1.5 m x 3.5 m at height $= 12 \times 0.15 = 1.8$ m. 6. **Length check:** $3.3 + 1.5 = 4.8$ m $\le 5.5$ m, so it fits; the spare 0.7 m is kept as entry/exit space. 7. **Check:** $2R + T = 2 \times 150 + 300 = 600$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.6^\circ$ (within 25-40 degrees). 8. **Waist slab:** effective span about 4.8 m, so depth $\approx$ span/20 $= 240$ mm; adopt a 250 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 | | | | LANDING | +- - - open well - - - - + | | FLIGHT 1 >>>>>> UP | | +------------------------+---------+ (arrows point up the stair) ``` ```text SECTION (not to scale) +---- upper floor 3.6 m _____| ____| flight 2 ______| landing +1.8 m ____| flight 1 _| ground floor +0.00 ``` #### Summary | Item | Adopted | |---|---| | Riser | 150 mm (24 nos.) | | Tread | 300 mm | | Flights | 2 flights x 12 risers | | Width of flight | 1.5 m | | Waist slab | 250 mm | **Answer: 24 risers of 150 mm and treads of 300 mm; 2 flights x 12 risers; flight width 1.5 m.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a functional requirement of a good staircase? A. Located through the middle of rooms for privacy B. Narrow width of 0.6 m even in public buildings C. Non-slip treads, handrail about 0.9 m high and headroom of at least 2.0-2.2 m D. Unequal steps to make climbing interesting Answer: C. Good stairs have non-slip surfaces, 0.9 m handrails, adequate headroom, equal steps and an accessible location. (Key point: Functional requirements) 2. A staircase where one wide flight splits into two narrower flights at a landing is called A. Quarter-turn B. Three-quarter turn C. Bifurcated (branching) D. Dog-legged Answer: C. A bifurcated stair has one wide flight branching into two narrower flights at a landing. (Key point: Types by shape) 3. For H = 3.6 m, R = 150 mm, b = 1.5 m and room width 3.5 m, what are the risers per flight and well width? A. 24 per flight and 0.5 m well B. 12 per flight and 2.0 m well C. 12 per flight and 0.5 m well D. 12 per flight and no well Answer: C. 24 risers in total, 12 per flight, 11 treads; well = 3.5 - 3.0 = 0.5 m. (Key point: Risers and open well) 4. With going 3.3 m and landing 1.5 m in a 5.5 m long room, what is concluded? A. 4.8 m is within 5.5 m so it fits; waist slab about 4800/20 = 240 mm, adopt 250 mm B. 4.8 m is more than 5.5 m so it fails C. 4.8 m fits; waist slab 48 mm D. Going + landing is 1.8 m; slab 90 mm Answer: A. 3.3 + 1.5 = 4.8 m <= 5.5 m; depth about span/20 = 240 mm, adopt 250 mm. (Key point: Length check and waist slab) ## Related in Building Technology - [Open-well staircase (6.0 m × 3.5 m hall)](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-064j) — Building Technology, chapter 5 - [Staircase for public building (5.5 m × 6.5 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-public-5p5x6p5) — Building Technology, chapter 5 - [Building shape in plan and elevation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Abuilding-shape-plan-elevation) — Building Technology, chapter 11 - [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× - [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 - [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 ## Related in other subjects - [Two-room building: brick plinth, door shutters, plaster](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Abuilding-m-two-room-three-items) — Estimating and Costing, chapter 6 - [Two-room building: excavation, PCC, brick, plaster](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Abuilding-h-two-room-fig1) — Estimating and Costing, chapter 6 - [Slab panel 2 for BM and SF (floor plan)](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aslab-panel-2-for-bm-and) — Design of RCC Structure, chapter 9