Correct Answer - Option 4 : stair width
The following are some of the general guidelines to be considered while planning a staircase:
1. The respective dimensions of tread and riser for all the parallel steps should be the same on the consecutive floor of a building.
2. The minimum width of stairs should be 850 mm, though it is desirable to have a width between 1.1 to 1.6 m. In a public building, cinema halls, etc., large widths of the stair should be provided.
3. Generally, the number of risers in a flight should be restricted to twelve.
4. The minimum vertical headroom above any step should be 2 m.
5. The minimum width of landing shall be equal to the staircase width.
6. The size of the tread generally ranges from 270 mm for residential buildings and 300 mm for public buildings.
7. The size of the riser generally ranges from 150 mm for public buildings to 190 mm for residential buildings.
