Different Parts of stairs – Suitable width of stair, and Function of each part

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Stairs are the structural comments containing a series of steps by means of which one can easily access different floors of the building. Stairs are medium for mobility over the entire floors of buildings. The different parts of stairs are given below.

Thus, It is located in common or easily accessible part or area of the building. And such area where the stair is located are called staircase.

The stair can be of different designs, shapes and also made up of different materials like wood, brick masonry, concrete (RCC), steel, etc. as required. But whatever material, design, and shapes are made their entire function is just to help in mobility over the different apartments.

Different Parts of stairs - Suitable width of stair, and Function of each part
Parts of stairs

Sometimes stairs help for the quick escape from apartments during emergency conditions like an earthquake, fire in the building, etc. Such stairs are generally provided at outdoor buildings and specially called emergency exit stairs, which generally remain close for normal use.

With the development of architectural and civil engineering, many improvisations over stairs are made. Stairs are not just made with the purpose of access but also with the safety, comfort criteria, and aesthetic value due to which stairs have additional components like railings, ballast, safeguards, nosing, etc.

Moreover, in some residential buildings and mostly in commercial buildings like supermarket, complex, auditorium, cinema hall, etc., these stairs are designed along with side ramps for better mobility of the carriers, trolleys, and wheelchairs.

The good staircase must be having well sufficient area for the landing, flights, entire length and width of the stair. The staircase must be well ventilated with the light and air.

The windows can be placed at the flight and landing side of stair. And direction of the staircase should always be located such that light can easily radiated on buildings easily. It is not always compulsive buy generally the running direction of stairs are prefer to be clockwise direction.

The width of stair must not be congested.  It should sufficiently wide enough so that luxury material like bed, sofa, cupboard, etc. and big household equipment like refrigerator, Washing machine can be easily transported.

The width of the stair should not be less than 900mm and 1800 mm for residential and public buildings respectively.

Before starting about different parts of stairs, I would like to tell you some few important things given below.

The minimum clear width of the staircase should be as follows:

  • Apartments (Shared) – 1000 mm (Within each multilevel unit) Internal – 800 mm
  • Auditoriums (Below 500 capacity) – 1500 mm
  • (Above 500 capacities) – 2000 mm
  • Hospitals – 2000 mm
  • Cold Storages and Warehouses – 1250 mm
  • Buildings more than 4 stories high – 1250 mm (Industrial or Commercial)
  • Recommended for other types of buildings:
  • Educational – 2000 mm
  • Residential – 800 mm
  • Cinemas (Below 500 capacity) – 1500 mm (Above 500 capacities) – 2000 mm 

Parts of stairs | Components of stairs

1) Steps :

Different Parts of stairs - Suitable width of stair, and Function of each part

Step is the smallest elementary component of the stair which helps in accent and descent. Step consists of series of combination of risers and consecutive treads. Each steps of entire stair must be identical. The step of the stair can be made of masonry bricks, or concrete or the wood depending upon the types of stair.

2) Tread :

It is the horizontal portion of step upon which the foot is placed while ascending or descending. And the horizontal distance between two successive riser faces is known as going. It must be noted that going doesn’t include extruded part beyond riser face (i.e. nosing).

The minimum tread shall be 250 mm excluding nosing. For residential building, it is adopted as 250mm and for public it is adopted as 270mm in Nepal.

3) Riser :

Riser is the vertical height area of single step that helps provide support for tread and connects two consecutive treads. However, the vertical distance between each two consecutive tread surface is known as the rise.

So, Riser doesn’t include the height of the protective layers like marble kept above the surface of the tread, but rise does. The maximum riser will be 175 mm for all buildings except for internal staircases of Apartments, which can be permitted up to 190 mm. For residential building, a rise of 160mm and for public buildings rise of 150mm is adopted in Nepal.

4) Landings :

Landing is a horizontal level platform area at the top or bottom of the support a series of some steps between them. Its major function is to provide change in direction.

But sometimes when the stair is too long covering horizontal distance, the number of landings is provided so that the pitch angle of the stair doesn’t get too small and also, provides the user to take a break on ascending and descending for a moment.

Landing must have a greater area than the tread of the steps. The width of landings is generally taken adopted as 1500mm – 1800 mm and length depend on the type of staircase adopted

5) Flight:

Flight is the series of consecutive steps without the break, which we simply had known as landing. In other words, it is single units of series of steps between two landings.

There can be a number of flights within two consecutive floors. This generally depends upon the type of stair, length of the stair, desired pitch angle, and vertical height between two consecutive floor slabs. The length of the flight can be accommodating with an increasing number of flights. The flight number can be made to 3 – 12(maximum) between two consecutive floors of buildings.

6) Waist slab /Strings :

It is the inclined slab support in stairs upon where the steps of stairs rest. There is a separate requirement of the RCC design of such slabs. Sometimes the waistcoats are supported with waist beam as well.

And in some stairs of steel and wood, the waist slab is excluded and instead waist beam of wood or steel section is provided.  It must not be confused with the waist and waist slab. Waist generally refers to the feelings or triangular area included between the Riser, Tread, and string.

7) Pitch of stair :

The Pitch of the stair is the slope angle at which the stairs or each flight of stairs is made. In other words, it is the angle between the floor slab or landing and the waist slab. The good design of stairs should not be too vertical or too sloppy. The pitch angle is limited within 25°-40° for the good design of stairs.

8) Run:

This is a very important part of the stairs to be considered. It is the total length of stairs in a horizontal plane including the landings. The run of the stair is a horizontal projected distance. One should not confuse it with the length of the flight.

Sometimes the protective tough and hardened layer of thin slabs of stone like marble and slate and wooden battens are placed over the top surface of trade in order to prevent the rapid deterioration of the tread surfaces.

And, such layers of marble or slate or wooden batten are projected beyond the face of the riser and length of the tread. The extruded parts are called nosing.  They provide architectural beauty as well as help to prevent the edge disintegration of the tread. The nosing is curved at the tip.

9) Scotia :

These are angle support provide between nosing and the face of risers.. Generally very important in the wooden nosing, and in such nosing angle section are prefer to support.

10) Soffit :

headroom

They are under the surface of the stairs. The distance between the tread or landing surface and soffit is called headroom and should not be less than 2.1m to 2.3m.

11) Railings :

Different Parts of stairs - Suitable width of stair, and Function of each part

The railings are structure attached on side of the stairs in order to made stairs more safe and comfortable. The railings prevent accidents such as the falling of children and adults. Moreover they also provide the support to the hand during ascending or descending the stairs. The major components of railings are,

Handrail: Its curved chamfered member of the wood and metal kept along parallel to the string of the stairs. It is the top inclined member of the railings at which people support their hands while climbing or descending.  Handrails are generally fixed on basis of line od nosing. Line of

12) Nosing:

Nosing is the tangential imaginary line to the nosing parallel to the string. Handrail should be between heights of 750mm- 900mm. The curvature diameter of handrail shouldn’t be less than 50mm for steel railings. For wooden the specific chamfered section are made by Carpenter.

13) Baluster:

The vertical member of wood or steel in the railings, kept at well spacing so that children may not passes from that, and to support the long Handrail above them. They are used to fence for user especially children while using staircase.

14) Newel post:

The vertical member usually thick in diameter kept at the end of flights and connects the end of the changing direction of the hand rail.

Types of stairs

  1. Straight stairs: There is no change in direction in such stairs. They occupy fewer staircase areas but genera have a long run, length of the flight, and high pitch angle.
  2. Turning stairs: Stairs having change direction while using. Generally adopted as it maintains a ratio of the run and with. And gives more accessibility in the building. The change in direction is generally preferred to be clockwise and made with the helps of landings. The winders are also used in such stairs. They are further divided into:
    1. Quarter turn stairs: The stairs which change its direction only a single time either left or right.
    2. Half turn stairs: The stair which changes the direction by 180° in each landing or flight. Commonly used type. Based on leaving space between the two stairs flights or not they are also classified as dog-legged and open-well stairs. Mostly adopted stairs on buildings due to easy design.
    3. Three Quarter turn stairs: The stair having three right angles between the two consecutive slab floors. Provision of open space in the middle of the staircase. Which can be used for ventilation, lighting purposes from the transparent roof?
    4. Bifurcated stairs: The single width span stair bifurcated at the top of the landings. Generally used in commercial buildings, auditorium, the complex where there is high mobility.
  3. Continuous stairs: Stair with continuous steps or winders. They have no breakage. Generally vertical in nature occupying very less space. Mostly use at towers and the top staircase for access to the roof. They can be:
    1. Circular: Generally made of steel and iron.
    2. Spiral: mostly used RCC for the emergency exit.
    3. Helical: Use in towers, lighthouse.
  4. Geometrical stairs: Staircase with different geometrical shapes like hexagonal, pentagonal, circular.

Things to Know

One must not confuse the stair with the ladder. The ladder is a vertical or inclined set up of rings or steps. They are generally used for temporary access. They are mostly made of wood, plastic, and metals like steel or aluminum. Some ladders are permanently fixed in building for access.

This is general adopted in the traditional building of Nepal and India made up of. Masonry blocks, and mud marram mortar before the introduction of the staircase. They are kept at an angle greater than 45°so can’t be called stairs.

Geometrical Design of stairs with parts of stairs

Plan a dog legged stair for building in which the vertical distance between the floor is 3.6 m. The staircase is of dimensions 2.5m X 5m.

The data required for the design are assumed in basis of standard specifications or value.

Assume,

Riser (R) = 15 cm

Tread (T) = 25 cm

Width of stair = 120cm

Given,

Vertical height (H) = 3.6m =360cm

Width of staircase = 2.5m =250cm

Total length of staircase = 5m =500 cm

Calculations:

Height of each flight for dog leg = 3.6/ No of flights = 3.6/2=1.8m

Number of riser in single flight = 180cm /15cm = 12

Number of tread in single flight = No. of riser – 1 (can be different for the middle flights in quarter turn) =11

Max. Width of stair = 250cm /2 =125cm.

So assume width of 120 cm is permissible.

Space between two flights = 125cm – 120cm =5cm

Also assume width of landing =120 cm then,

Length occupied by tread = 11 * 25cm = 275 cm

Length of remaining passage = total length –  length occupied by tread –  width of landings =105cm

This can be presented in drawing as:

Different Parts of stairs - Suitable width of stair, and Function of each part

I hope this article remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Rajan Shrestha

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