Correct Answer - Option 1 : 25 to 30 cm
Explanation:
As per the Indian National building code: 12.18 Staircase/Exit Requirements
12.18.1 The minimum clear width, minimum tread width, and maximum riser of staircases for buildings
12.18.1.1 Minimum width - The minimum width of the staircase shall be as follows:
(a) Residential buildups (dwellings) 1.0 m
NOTE— For row housing with 2 storeys, the minimum width shall be 0.75 m.
(b) Residential hotel buildings 1.5 m
(c) Assembly buildings (like auditoria, theatres, and cinemas) 2.0 m
(d) Educational building 1.5 m
(e) Institutional buildings 2.0 m
(f) All other buildings 1.5 m
12.18.1.2 Minimum tread: The minimum width of tread without nosing shall be 250 mm for residential buildings. The minimum width of tread for other buildings shall be 300 mm.
12.18.1.3 Maximum riser: The maximum height of the riser shall be 190 mm for residential buildings and 150 mm for other buildings and these shall be limited to 12 per flight.
12.18.2 The minimum head-room in a passage under The landing of a staircase shall be 2.2 m. The minimum clear head-room in any staircase shall be 2.2 m.
