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The calculation of dimensions of a spiral staircase is very critical and performed with utmost care. It takes daring shape and configurations compared to the conventional staircase.
There are BIM and other software to determine the spiral staircase dimensions. But it is essential as a civil engineer to know the restrictions and basic concepts within the design of the spiral staircase.
Among different configurations taken by spiral staircases, the most common is the circular format. Here the determination of the dimensions of a circular spiral staircase is explained.
Also Read: What is Spiral Staircase?
Design of Spiral Staircase
The three crucial factors taken into consideration while designing a spiral staircase are:
- The height of the vertical rise of the staircase
- The angle of rotation of the staircase
- The diameter of the staircase
Based on the plan, develop a proper idea about where the stair starts from the bottom floor to where the stair stop at the top level. It gives the height of the vertical rise of the staircase. The stair diameter is used to determine the angle of rotation.
Steps to Design a Spiral Staircase
1. First, take the dimensions of the stairwell opening. A spiral staircase has a 100mm smaller diameter than the given stairwell opening. (As per BS5395-2 1984).This provision makes the stairs to fit comfortably in the given space.
For example, a stairwell opening of a square dimension 2000 x 2000mm can accommodate a staircase diameter of 1900 x 1900mm. Determine the number of steps for a single turn, i.e., for 360 degrees. The value of the steps for different stairwell opening are mentioned in the table below.
2. Determine the floor to floor height. Take the recommended value of risers from the standard table-2 given by BS5395-2 1984. For example, if,
- Floor height 'h' = 2700mm
- Riser 'r' = 225
- No of risers =2700/225 = 12
- No: of Steps = 11 + 1 landing platform
Check the obtained values with the building regulations of the given area or country.
3. The landing platform is the next element to design. The landing platform can be either square, round, or trapezoidal. Square landing platform is not recommended as it reduces the head clearance.
Locate the landing slab according to the space available at the staircase exit. Choose the best position for the landing slab.
4. Develop a spiral staircase layout with the obtained details. Draw a rough sketch on where the entry step starts. When drawing manually, it is better to start from the landing platform in a downward movement. Or choose any stair calculator available on the web. Below shown is a spiral staircase design.
5. Always check for head clearance. The head clearance of a spiral stair is the height under the landing platform when moving down the stair. Head clearance must take a minimum value of 2m to avoid head bumping on the landing platform edges.
Always go through the staircase building regulations before getting to construction.
The material used for spiral stairs can vary depending on the choice of the client. Classic style stairs and modern style can be chosen based on the preference.
Also Read: Design Requirement of Staircase
Also Read: Components of Staircase