Calculate Step Heights/Stair Dimensions According To DIN 18065

Calculate Step Heights/Stair Dimensions According To DIN 18065

A staircase is a building element that is used every day. However, their production is very complicated and should only be carried out by professionals. To ensure that consistently safe stairs are used in all buildings, their manufacture was specified in DIN 18065. An improperly built staircase is a very serious construction defect. As a builder, you have the full right to demolition and correct implementation. In this text, you can read how to calculate and check a staircase.

The natural stride length as a basis

The step rule is the most important formula for every craftsman who deals with staircase construction. In addition to carpenters and stair builders, these are mainly concrete workers and bricklayers. Only a stair made according to the step rule satisfies DIN 18065 and thus has the necessary safety when going up and down.

The basis of the step measure is the average step length of an adult human. Although the body heights of people with 1.60 m – 1.90 m form a fairly large spread in average height, the inseam length remains relatively constant at approx. 61 – 65 cm.

That’s why DIN 18065 defines a step length of 63 centimeters as the average.

From this measurement, the rise and aspect ratio of a stair build.

Increment in a staircase

Stairs are designed in such a way that they can be walked continuously by a healthy, adult person. This means that one step usually takes two steps. This construction also allows the “triple step”. This also enables elderly and disabled people to use the stairs. Step by step you climb with both feet.

Based on the average step length, this must be broken down into two climbs and one step. A simple division by three would make the slopes and tread equal. At 63 cm: 3 = 21 cm, however, it turned out that the steps are still a bit too steep and the tread is a bit too narrow to be able to use the stairs comfortably. That’s why the incline was reduced by three centimeters and the tread widened by six centimeters.

The standard size for a staircase is therefore:

  • 18 centimeters per slope
  • 27 centimeters per step width

In order to achieve more flexibility on site, this rigid specification is expanded with a slight variance. The step width or the step should be between 23 – 29 cm. Nevertheless, the sum of two gradients plus a step must always be between 59 and 65 centimeters. Therefore, although a variance is permitted, this then necessarily prescribes the dimensions of the other component in each case. The following ratios of step height to step width are therefore specified:

  • 17/29
  • 17.5/28
  • 18/27
  • 18.5/26
  • 19/25
  • 19.5/24

This dimension is found in all normal, straight or platform stairs. In the case of spiral staircases, rigidly adhering to this dimension has proven impractical. Therefore, a slight deviation from the standard dimensions is permitted for spiral or curved stairs.

Determine the shell dimensions

Now it is relatively easy to calculate the stairs in such a way that they can be used permanently. But there are still some traps lurking along the way. Basically you measure from the upper edge of the unfinished floor to the upper edge of the unfinished floor of the next floor in order to get the overcoming dimension. The first mistake you can make here is not considering the thickness of the floor. Therefore: Always measure from top edge to top edge!

The normal room height in a detached house is at least 2.10 meters, but the rule is between 2.20 and 2.50 meters. Room heights of only two meters or less are mostly felt by the residents as oppressive and uncomfortable, even if they themselves are significantly smaller than 2.00 meters. The thickness of a concrete intermediate ceiling is between 16 and 20 cm in normal single-family houses. This gives you a shell of 2.40 meters to 2.70 meters, which the stairs have to overcome.

Calculation of stair steps

This dimension can now easily be divided by the specified standard heights for stairs. Starting with a clear shell height of 2.70 meters, the number of steps is:

270cm : 17cm/step = 15.88 steps

However, since partial steps are never used, at least 16 steps are now assumed. Now you take the clear shell height again and divide it by the calculated number of steps:

270cm : 16 = 16.875cm

This gives the height of a single step. With the help of the increment rule 2 x S + A = 63 cm , the width of the step surface can now be calculated:

16.875cm x 2 + A=63cm 33.75 + A= 63cm A=63cm – 33.75cm = 29.25cm

However, since you now know that the finished staircase will have 16 steps and each step except for the last one will have a width of 29.25 cm, the length of the staircase can now also be determined:

15 x 29.25 = 438.75 cm or 4.39 meters

The stairwell must be at least this length in order to be able to climb the stairs safely without hitting your head.

Shell size is not finished size!

This method is useful for temporary construction stairs or for retrofitted wooden or steel stairs. For concrete stairs, however, caution is called for here, because it is very easy to make a construction error.

There is another aggravating factor: the staircase must have the standard rules in the final installation state, not already in the shell! Both the floors and the stairs themselves are usually still occupied so that all height ratios change. For example, if the lower floor has a screed with built-in heating and the upper floor has strong floor insulation, then all the dimensions are no longer correct. Coating the stairs with thick marble slabs also results in different step heights than a thin coating of tiles or PVC. It is therefore important to know in advance exactly how the stairs and floors are to be covered. The height of the coverings must be included in the calculation of the stairs. If you forget even one factor, the staircase will become so wrong in construction that usually only a reverse is possible. A single step that is too low or too high makes the entire staircase very unsafe and becomes a constant source of danger.

Which stairs to take?

A stair length of more than four meters is just about acceptable. Longer staircases have the disadvantage that they become very impractical when transporting loads. DIN 18065 prescribes an interruption by a platform after 18 climbs at the latest, even in the case of straight stairs. However, this slope can be used to change the direction of the stairs. Platform stairs also have the advantage that loads can be placed well on them. They are particularly suitable for rental apartments. That is why platform stairs are found as standard in the stairwells in apartment buildings.

Half-turn stairs allow straight stairs to change direction. A change of direction of 90° or at right angles is usually carried out. If a complete change of direction of 180° is to be carried out, the platform staircase is more recommended overall. It is much easier to build and offers much more space when transporting loads.

Would you like to learn more about the different types of stairs? You can find a detailed description here:  Overview of the types of stairs

Installation or shell construction stairs – advantages and disadvantages

The standard in single and multi-family houses is the covered concrete staircase. This also fulfills static tasks. It is anchored to the storeys with heavy reinforcement irons, giving the house additional stability overall. However, their installation is quite complex: if no concrete prefabricated staircase is used, it must be calculated, shuttered, reinforced, poured and shuttered again. It will later be coated so that it fits in with the rest of the house both visually and functionally.

A subsequently built-in staircase gives a much greater design variety. It does not always have to be the standard wooden staircase. Today’s stair builders can also produce marble stairs for retrofitting. Nevertheless, the subsequently installed stairs never reach the stability of a concrete staircase that is firmly anchored to the shell. The subsequently installed stairs can hardly take over static tasks. On the other hand, their calculation is much simpler. In addition, subsequent changes to the building are much easier to implement. An unplanned underfloor heating with a thick insulating layer always creates an irregularity in the slope of concrete stairs. With a built-in staircase, the staircase can either be replaced or slightly modified.

In terms of price, however, it depends very much on the version as to which solution is cheaper. A pure prefabricated concrete staircase with 15 steps costs at least 1200 euros. Add to that the decking and railings, which can quickly more than double the price. Professional coating is also important for concrete stairs: If the steps are laid without a floating screed, every stairway can be heard loudly throughout the house. This can also lead to a construction defect where a correction can be sued for. A built-in staircase is priced similarly. However, it can be used immediately after installation. A handrail is usually built in.

Conclusion: Good planning saves costs

There is hardly any other building element where you can make as many serious mistakes as you can with a staircase. A measurement is miscalculated and the staircase has to be completely rebuilt. Corrections are very difficult to implement and usually lead to unsatisfactory solutions. That is why good and sustainable planning is the most important thing when it comes to a staircase. All factors must be taken into account, including potential later installations. But if you take enough time and professional advice, the staircase becomes a reliable, elegant and functional part of the house.