Information on geometry, slip resistance, lighting, and markings
Many issues have to be borne in mind when designing stairways. The central concern is to ensure they can be used safely. This page summarises the most important requirements.
Blondel's formula has to be followed when designing the geometry of safe steps.
Stairway dimensions and geometries
Steps
For an unimpeded sequence of movements on a stairway, its dimensions must be based on the length of the human stride. What is known as Blondel’s formula is a long-established tool for planning stairways with medium pitch angles.
a + 2s = SL
a = going
s = riser
SL = stride length
Blondel's formula should be applied to stairways with stair slopes between 24° and 36°. Stride lengths of between 59 and 65 cm are to be preferred for good ease of use. Stairways with an slope of 30°, a going of 29 cm, and a riser of 17 cm have proven to be particularly safe for users.
The general rule is that the steeper the stairway, the greater the stride length selected should be.
Steps are deemed to be adequately sized if they comply with the following dimensions:
a = 26 … 32 cm
s = 14 … 19 cm
Step dimensions of a = 29 cm and s = 17 cm are considered ideal.
Furthermore, there must be no variation in the dimensions of the risers and treads on a stairway that connects two storeys. Different formulas are applied for the calculation of steep stairways with higher slopes and shallow outdoor stairways (see the publications below).
Landings
Landings serve to reduce the physical strain involved in climbing stairs.
The rule is that a landing has to be provided for after eighteen steps on stairways with medium slopes (up to 36°).
The landing depth should be calculated as a multiple of the stride length. It should be based on an odd number of strides because this is consistent with human kinetic symmetry and gait rhythm.
Stairway geometries
A stairway may consist of several flights of steps connected together by landings. A distinction is made between stairways with straight and winding flights. Stairways with winding flights are not permitted for certain purposes.
Stairway widths
The widths of stairways depend on their intended use and the number of users. For stairways leading to workstations in permanent use, the minimum width is 1.0 m. Smaller dimensions are also allowed for rarely used stairways that are not required by building law (see the publications below). Greater widths are essential on stairways where users could be walking in both directions at the same time.
Railings and handrails
Railings are required on the unenclosed sides of stairways and provide protection against falls. Furthermore, railings have to be designed so it is not possible to fall through them, with a knee rail for example.
The railing height depends on the vertical drop in each case:
- vertical drop up to 12 m: railing height at least 1.00 m
- vertical drop greater than 12 m: railing height at least 1.10 m
However, alternative requirements may apply under building law.
The fundamental rule is that if a stairway is also going to be used by children, attention has to be paid to ensure the railing design is childproof.
Children are keen and particularly agile climbers. Railing designs with horizontal bars, such as knee rails, are therefore not childproof. In this case, it is safer for railings to have vertical balusters spaced a maximum of 12 cm apart.
The handrail is another safety feature that has to be considered. It has a supporting function, stabilising users who walk unsteadily, offers guidance for people with disabilities, and should be installed at a height between 0.80 and 1.15 m. Its profile should be ergonomically designed and allow it to be gripped securely, which is why flat materials with sharp edges are not suitable.
Slip resistance, lighting, and markings
Slip resistance
Steps should be characterised by the same slip resistance as the adjoining areas. The slip resistance of their treads and nosings should be identical if possible. Where auxiliary non-slip nosing systems are installed, they should not protrude upwards in order to prevent tripping. Furthermore, the depth of the nosing systems selected should depend on the stairway pitch.
Lighting
Adequate lighting is also important. It is essential if users are to look ahead and judge the geometry, condition, and course of the stairway, as well as noticing any danger spots.
Pursuant to Technical Rule for Workplaces (Arbeitsstättenregel) ASR A3.4, a illuminance of 100 lx is the minimum required for indoor traffic routes with stairways along them. However, there are no separate specifications for the lighting of outdoor traffic routes with stairways in ASR A3.4; which merely demands 5 lx generally for outdoor footpaths.
The figures given are minimum values. Higher illuminances are to be stipulated specifically if they are found to be necessary by a risk assessment. This is particularly to be recommended for stairways along outdoor traffic routes.
Markings
Steps can be made easier to recognise with coloured markings. It is to be recommended that at least the first and last steps of a flight of stairs be identified with coloured markings. Should it not be possible to connect areas of different heights with a ramp, a sequence of at least two consecutive steps is allowed, which are to be marked in accordance with ASR A1.3.
Stairways along escape and rescue routes
Permissible stairway shapes
In workplaces, stairways with straight flights are to be preferred to stairways with winding or partly winding flights. As a matter of principle, only stairways with straight flights are to be provided for, in particular on escape and rescue routes. Winding and spiral stairways are merely permissible on secondary escape routes, and then only if the results of a risk assessment give reason to believe they will be used safely in the event of an emergency.
Required stairway widths
Widths for routes designed for the movement of people within workplaces are specified in ASR A2.3. Stairways must not be narrower than these widths so that they do not become “bottlenecks” along escape and rescue routes. The clear widths of stairways leading to permanent workstations and stairways required by building law should be 1.0 m at least. The width and course of the stairway and the entire stairwell should permit a person lying on a stretcher to be carried by this route.
* Supplemental sheet 1 (Jan. 1997) for DIN 18065 technically introduced the definition of a minimum width of 1.0 m for stairways required pursuant to Building Law as a technical building specification via the building ordinances of the federal states.