A spiral staircase system constitutes a spiral arrangement of steps or treads. Usually, treads are attached to a central vertical post or column and rotate about it when we move up or down the stairs.
Tread may also be attached to the circular peripheral wall without a central post. Consecutive steps have a constant value of riser and angle of rotation.
This gives the staircase a peculiar, unique design and aesthetics. These staircases may or may not consist of handrails. Spiral staircase can be constructed using materials like glass, steel, concrete, wood, etc.
Spiral staircase dimensions should be carefully prepared. Spiral staircases are usually considered as a means of secondary excess.
These are constructed in addition to the primary staircase to enhance the aesthetics and interior of the rooms because of their compactness (occupy smaller space) and availability of various choice of geometric design and handrail types.
Spiral staircases are also preferred to provide excess to loft expansion, terrace, and the area which have limited accessibility and less load.
Because they occupy smaller space than other types of staircases and saves precious spaces. They can be constructed anywhere, inside or outside, providing minimum support structures i.e. a vertical column.
In contrast, they also have been used as means of the primary staircase in various historical monuments like Dharahara. With the implementation of proper design parameters, they can be constructed as a primary staircase as well.
Major factors that influence the design of the spiral staircase are mentioned below. Different Spiral staircase dimensions are also given.
The height of the spiral staircase is the most important factor affecting the design. It is evaluated by measuring the floor height between consecutive floors i.e from the bottom floor to the consecutive upper floor where the landing of the staircase is placed.
In Nepal normal floor height is about 9’4”. Riser of the steps is determined from the building codes of the respective area. Normally it is taken as 190mm or 179mm i.e. (7.4” or 7”) in residential houses for straight and L shaped staircase.
Since the spiral staircase is for secondary purposes riser can be taken up 9.5”. Riser and floor height is used to calculate the no. of steps which are equivalent to Floor height/riser. The result includes the land platform as a step.
All steps radiate from the central column and rotate at a certain angle when moving up or downstairs. The angle of rotation is preferred as 30 degrees mostly.
The number of steps and angle of rotation can be used to calculate the number of revolutions of steps in the spiral staircase as (number of steps * 30 degrees) / 360 degrees.
The diameter of the spiral staircase depends on the opening provided on the ceiling which is determined from the respective code. It may vary from 3’3” (1000mm) to 6’6” (2000mm) depending on load and capacity required.
Other minor factor includes styles of tread and handrails, aesthetics, and functionality.
Table 1 Recommend dimensions of spiral staircase is tabulated in the following table in accordance to British standardSpiral staircase Dimensions
Table 2 BS standard for determination of stairway diameter and riser
No. of steps = floor height / riser = no. of treads including landing
I hope this articles on “Spiral staircase dimensions” remains helpful for you.
Happy Learning – Civil Concept
Contributed by,
Civil Engineer – Jenish Shakya
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