The layout of a staircase leaves nothing to chance. In order for your new staircase to meet your exact needs, the calculation of its dimensions – and in particular the steps – requires great precision. Does it seem complicated to you? Here are all the calculation rules to obtain the ideal staircase. And it’s actually quite simple…
The staircase primer: a few key words
Before going further, here is the technical vocabulary that will help you understand the structure of a staircase. Better to know what we’re talking about, right?
- Wilting: This is the passage width of the staircase. As we must be able to meet someone, the recommended step is at least 80 cm.
- Breakaway: This is the clearance height, between the step and the ceiling. The breakaway must be at least 1.90 m. In principle, it is equal to a ceiling height, i.e. 2.50 m.
- Giron. : This is the horizontal distance between two nosings, i.e. the depth of the step. The length of the tread must allow the foot to be placed completely on the step, which ensures the stability of the climber. The bosom ideally measures between 26 and 30 cm.
- Limon : Whether wood, concrete or steel, the stringer is the structure of the staircase. The steps rest on its uprights, which rest on the landings.
- Marche : This essential element is the flat surface on which you put your foot to climb the staircase. The step is defined by its height (which we will learn to calculate) and by its tread. The vertical part, named riser, does not exist in exterior stairs and milling stairs. The steps are “straight” (rectangular) or “balanced” (trapezoidal).
- Landing : At the end of a flight of stairs, we reach a platform, the landing.
- Ramp : To climb a staircase in complete safety, a guardrail is provided: the ramp. Attached to the silt, it consists of two posts, a handrail and balusters. Some more minimalist staircases prefer to do without it.
- Setback: It corresponds to the space available on the ground, often limited by the frame. The size of the setback may make it necessary to choose a winding staircase instead of a straight one, which requires more space.
- Hopper: To pass from one level to another, the staircase passes through an opening which crosses the floor. This is the hopper, most often fitted out with wooden joists. Square, rectangular or L-shaped, its dimensions adapt to the passage of a person.
- Volley: It is the group of steps between two landings.
Now that you know the elements of a staircase, you still have to know the three types of structures. A staircase is generally supported by a structure at two stringers side. But there are also stairs single stringercentral, and stairs hanging, whose design is independent of an apparent load-bearing structure. You didn’t catch everything? Don’t worry, no written quiz is planned on this primer…
What will your staircase be used for?
The calculation of the steps meets the requirements of an ideal staircase: the one you use every day without thinking about it. Climbing the stairs should be done without too much effort. It is therefore appropriate to question the use of your staircase.
- Who are the people who will borrow it? Young children, people with reduced mobility…?
- Is it a daily or occasional use staircase?
- What is the desired passage width? Should we be able to transport furniture, for example?
- What is the arrival access? In a hallway, a room, a mezzanine…?
In the case of daily use, two aspects are essential: security et comfort. And that counts in the calculation of the steps! Their size must correspond to a certain ergonomics, a necessary condition to preserve the health of those who use the stairs several times a day. Usually, the width of a straight staircase is 90 cm and its angle is between 25 and 42°.
What is the ideal step height?
The comfort of a staircase depends a lot on the size of its steps. And that owes nothing to chance. The dimensions of a staircase determine the size of the steps.
- For ease of use, the height of walking is between 16 and 20 cm. The ideal being 17 cm, the standard size. The higher the step, the steeper the stairs… and more tiring.
- For constant progression, all steps are height equal.
- In an interior staircase, the lap is between 26 and 30 cm. It can be smaller in the case of exterior stairs or used occasionally.
The step height is also defined in relation to the retreat and at the hopper available. Hopper is small, lack of space? Reduce the tread and increase the height of the steps (for example, aim for 20 cm). Otherwise, get as close as possible to 17 cm.
What is certain is that you must start by defining the desired height of the steps before calculating the number. You will then refine their precise pitch.
How many steps do my stairs need?
Taking into account the previous elements, the number of steps is calculated in a very simple way. Simply divide the total height of the stairs by the height of each step.
Let’s recap! For a staircase of daily use, we know that the ideal step height is 17 cm. How to deduce the number of steps of your staircase?
Ex 1: number of steps in a straight staircase
Suppose your straight staircase is 2.80 m high (i.e. 280 cm), which corresponds to the total height of the floor. You have decided that the steps will be 18 cm high. We start by dividing 280 by 18 cm. Result: we get the figure of 15.55. It is therefore necessary to round the result to 15 or 16. What to choose? A staircase with 15 steps of 18.6 cm or with 16 steps of 17.5 cm? Generally, we opt for fewer steps. Here, we therefore favor a staircase with 15 steps. But it is up to you to decide according to your use. If you want lower steps, more accessible to children for example, choose the option with 16 steps.
Ex 2: same for a quarter-turn staircase
The staircase is 2.9 m high, or 290 cm floor to floor. You want 18 cm steps. So we divide 290 by 18. The result is 16.1, which we round up to 16 steps. To get the exact step height, divide 290 by 16; they will therefore be 18.12 cm high.
Suppose you want higher steps. Go to 15 steps and redo the calculation. This time, the steps are 19.33 cm high. We stay in the nails, since, as we have seen, the height of a comfortable step can be between 16 and 20 cm.
Ergonomic staircase: use Blondel’s law!
With this brilliant formula, you are assured of a perfectly sized staircase for effortless use. It was in the seventeenth century that the architect François Blondel calculated the ideal relationship between height and the lap of a walk. The goal: a constant climb, a natural stride, minimum effort. In short, perfect ergonomics.
Here is the formula of Blondel’s law to calculate the ideal step for users: 2h + g = 63. Clearly, the relationship between step height and tread is consistent if it respects this calculation: 2 step heights + 1 tread = 63 cm. For Blondel, a result of 63 is the one that allows you to climb the stairs with the lowest energy expenditure. But this figure can be between 60 and 64 cm; it is the fork that guarantees sufficient comfort. In construction, the value of 61 cm is frequently used.
Check the ergonomics of your staircase: examples
As we have seen, the calculation of the number of steps is quite simple. For a staircase 300 cm high, with a step height of 17 cm, we obtain 17 steps. If your staircase is 250 cm and your steps 20 cm, you will have 12 steps. And so on.
But it is also necessary to check the ergonomics of the staircase to ensure that it is comfortable enough to use. This time, you need to use two parameters: the height of the steps and the length of the tread.
- The step height is 17 cm; the length of the tread is 27 cm. With Blondel’s law, you get a result of 61 cm. Ergonomics is good.
- The step height is 17 cm; the length of the tread is 24 cm. Blondel’s formula gives a result of 58 cm. Bad ergonomics!
If you are slipping in your calculations, do not hesitate to use online calculators dedicated to stairs. But you already know everything to calculate the height of the steps of your staircase like an architect!