Stairs types and dimensions of stairs
Stairs comprises of several steps which are arranged in a single flight or more number of flights.
A good stair should have the following characteristics :-
a) Width: 0.9 m in residential buildings and 1.5 m to 2.5 m in public buildings.
b) Number of Steps in a Flight: Highest number of steps in a flight should have been restricted to 12 to 14, whereas lowest is 3.
c) Rise: Rise should be identical. It should normally be 150 mm to 175 mm in residential buildings whereas it should be among 120 mm to 150 mm in public buildings. However in commercial buildings more rise should be arranged from point of view of economic floor area.
d) Tread: Horizontal extension of a step in a stair case is known tread. It is also called going. In residential buildings tread should be 250 mm whereas in public buildings it should be 270 mm to 300 m
To determine rise and tread, the following empirical formula is applicable : 2R + T > 550 mm but < 700 to 600 mm; where R stands for rise in mm and T stands for tread in mm.
e) Head Room: Existing head room in the stair case should not be under 2.1 m.
f) Hand Rails: Hand rails should be arranged at a suitable height of a normal person that ranges from 850 mm to 900 mm.
Classifications of stairs: The stairs are constructed with wood, concrete masonry or with cast iron. Wooden stairs are not fire-resistant and should not be used. However they can be utilized in insignificant buildings to get entry to small areas in the upper floors. Cast iron or steel stairs in the spiral forms are normally utilized to shorten stair case area. In several residential buildings, masonry stairs are found. Reinforced concrete stairs are extensively utilized in different types of buildings.
Depending on the shapes, the stairs are categorized as follow :
(a) Straight Stairs: If the existing space for stair case is constricted and long, straight stairs are useful. The purpose of these types of stairs is to provide entry to porch or as emergency exits to cinema halls. Under this type, all steps are provided in one direction. They may be arranged in single flight or in two flights with landing among the two flights.
(b) Dog Legged Stairs: It comprises of two straight flights with 180° turn among the two. They are generally utilized to provide entry from floor to floor.
(c) Well or Open-newel Stairs: It is different from dog legged stairs in order that there is 0.15 m to 1.0 m space among the two nearby flights.
(d) Geometrical Stair: This type of stair has similarity with the open newel stair apart from that well formed among the two adjoining flights is curved. The hand rail arranged is continuous.
(e) Spiral Stairs: These stairs are generally applied as emergency exits. It contains a central post that provides support to a series of steps provided in the form of a spiral. At the end of steps continuous hand rail is arranged. Such stairs are useful where very narrow space exists for stairs.
(f) Turning Stairs: Besides, dog legged and open newel type turns, stairs may turn in different shapes. They are based on the existing space for stairs. Quarter turned, half turned with few steps in between and bifurcated stairs are examples of such turned stairs.