One of the most critical calculation while planning any type of building be it residential, commercial or industrial is planning its staircase.
The calculation is easy but the way it is implemented on the ground is more important. Because experience says there are more demolitions of staircase than the perfect construction.
Before we start any calculation let us get familiarized with the parts of a typical stair.
Let us study the below drawing.
This is a sectional elevation of a staircase flight. A typical staircase will have following parts :
So, What is a staircase?
A staircase or a stairway is a structure which is provided to go from one level to another level in a building. The staircase consists of different parts. Let us have a look.
Parts of a staircase:
Flight is a part of staircase which connects two landings. It is a run of steps.
Landings are different levels in a building or an additional level between two floors of building.
Total Run is horizontal distance to be covered by stair.
Total Rise is vertical distance to be covered by stair.
Steps consists of two parts riser and tread. steps can be made in brick or concrete both.
Tread is the part of a step which you put your feet on and climb the stair.
Riser is the vertical part of a step. This is how much you climb when you go from one step to another.
There are some more parts which I have not shown in the drawing.
Nosing is edge of each tread which protrudes onto the tread beneath. The function of nosing is to provide anti-slip arrangement for the safety.
Handrail is an integral part of any staircase. The function of handrail is to prevent falling from the stair.
Now, lets get to the actual part. The calculation of the tread and riser.
- The minimum tread width generally is 250mm.
- The Minimum riser height is 150mm.
Please note that these are not the rules these values changes according to the type of building, use of building and prevalent codes and standards.
For Example : A hospital building will have a lesser riser height and more tread width than any other building because it is to be used by the people who are sick and their attendants who help them to climb.
So the formula is :
No. of Risers = Total Rise / Height of Riser
No. of Treads = Total Run / Width of Tread
Now, This is not it. More than often conditions are not so simple and you can not just provide the standard riser and treads. The total run and total rise are not in perfect ratio for that.
So we need to back calculate riser height and tread width. and than calculate the nos. This sometimes become a trial and error exercise.
Let’s take an example.
Let’s assume total run (total space – width of landings) we have is 3000mm and total rise we have is 2500mm.
We shall calculate how many treads can be accommodate in this space.
So, the possible no. of treads assuming tread width as 250mm
= 3000/250 = 12 Nos.
Now, The rise = 2500/12 = 208.33mm
Now, this rise of 208.33mm may not be acceptable according to the standards. So, What we have to do is we need to reduce this rise and recalculate no. of risers and treads here please note that tread width is also has to be within limits.
Hope the post proves to be useful.
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