# tread width, riser height, number of steps (video)

A spiral staircase is an option popular with owners of small premises, as its design allows to save space considerably. According to most newcomers to construction and renovation, making such a ladder is much more difficult than marching. This is not true. It is necessary to study in detail the design features of such a structure and adhere to the recommended procedure for its construction in order to obtain a reliable and durable result.

Scheme of a metal spiral staircase.

## Design rules

For safe operation of the stairs, its parameters must be selected in a special way:

1. The optimal width must be at least 80 cm. This will allow free passage to one person.
2. The average step width (treads) should vary between 25-30 cm. This value is based on data on the average width of a person’s stride.
3. The riser height should correspond to an interval of 15-20 cm. This value is also based on the average stride width.
4. The most convenient angle of inclination at which the structure does not become too bulky is 30-40 °.

Stair climbing steps.

The features of spiral staircases should be considered. In such constructions, the upper part is above the person. So that he does not have to constantly bend down, the height of the risers is not recommended to choose less than 17 cm. It is more convenient to use the staircase that contains an odd number of steps. Safe handrails should be from 90 cm to 120 cm.

It is necessary to check the staircase parameters by the following relation: ab = 12-14 cm, a + b = 45-47 cm, where a is the width of the tread b - riser height.

## Geometrical calculation method

Before performing the calculations, it is required to determine the location of the staircase, the place of entry on the lower floor and the exit point on the upper floor.

The main nuance that must be taken into account at this stage is the height of the passage. A person should calmly rise and fall without having to bend his head.

The first stage of the calculation is the determination of the height of the steps. First, their number is determined. To do this, divide the height of the floor by the recommended height of the riser. If the result is 2.8 m, then the following calculations are performed: 280/17 = 16.47. It is recommended to install structures with an odd number of steps, therefore, take their number as 17. Accordingly, the height of each will be equal to 16.47 cm. The resulting value is rounded to 16.5 cm. All steps, except the lower one, will be equal to 16.5 cm ( ), and the first - 16 cm.

Next, the width of the tread is calculated. At this stage of the calculation, it should be noted that the person walks at a distance of 1/3 of the width from the outer edge of the stairs. With a width of 1 m, a person travels in one ascent (or descent) a distance (L) equal to the circumference (its diameter is 100 cm * 2/3).

L = 2 * 3.14 * 100 * 2/3 = 418.7 cm.

This distance should be divided by the number of steps, reduced by 1, so as the upper stage will be located flush with the platform of the upper floor. It turns out: 418.6 / 16 = 26.2 cm. This value falls within the specified recommended interval, therefore, is taken as the calculated one. With such a tread width, the exit on the top platform is strictly above the entrance below. However, this is not possible in all rooms. Therefore, the calculations will need to be adjusted, taking into account the degree of rotation of the spiral staircase.

After correcting the data obtained as a result of the calculation, it remains only to complete the installation of the structure. Its installation is also carried out according to certain rules and regulations.