How to design stairs with a BIM model ready for download
Read our complete guide on how to design stairs, with general design criteria, renders, DWG CAD drawings and a 3D BIM model ready for you to use
In this guide we’ll be focusing on how to correctly design stairs and analyse the main features of various stairs types.
Below you’ll be able to download the complete BIM project example of a staircase together with a 3D rendering and the trial version of Edificius, the architectural software used to produce them.
Download the complete 3D BIM model file (in the Edificius native file .edf) with different types of stairs
Stairs are structural elements that allow the connection between different floors of a building. Generally a staircase is made of:
Stair steps are horizontal supports that follow one another upwardly, allowing users to ascend or descend a staircase and pass from one floor of a building to another.
A stair flight is a run of consecutive stair steps. A staircase can be composed of several stair flights which are separated by landings.
A landing is a horizontal element that allows the connection between two or more flights. It provides a resting place and allows the access to the different zones of the stairway. There are floor landings (that give access to the different areas of the floor) and intermediate landings (that connect the flights between them).
The vertical portion between each tread on the stair is called rise/riser. The depth of the tread is called run or going.
Staircase interior design. Types of staircase
Stairs can be classified by material:
- Concrete stairs
- Steel stairs
- Wooden stairs
The most common types of concrete stairs are:
- Rampant slab staircase: made by a concrete slab on which steps lay out. Structurally the slab is supported by a starting beam and an arrival beam.
- Knee-portal staircase: made by particular emerging beams, called knee-portals, because of its particular “z”- shape on which cantilevered steps are inserted.
Staircases may be classified also by slope. According to this criteria, we have:
- Ladder stairs, , almost vertical, with steps that can be used as handholdsin case of a very high slope (more than 50°); for maintenance, occasional or similar uses only.
- Common stairs, with a slope angle between 20° and 45°; for private uses, these normally have a larger slope value.
Staircase interior design, types of stairs
When choosing the form of the staircase, the available space and the position that the stairway should take, will influence the choice.
Choosing one model or another, means making the most of a wall space or a corner, or even the center of a room.
The form of the staircase in floor plan determines its type which can be a regular or irregular polygon, a circle or an ellipsis, etc.
Steps should always be perpendicular to the staircase walls in order to concentrate any irregularities along the landings.
The staircase can be configured in plan as:
- a rectangular plan, meaning that it has enough space for two parallel flights, that connect with floors or intermediate landings;
- a square plan, normally used to make the stairway turn around an elevator shaft;
- a circular plan (or helical, in some case), when we talk about spiral stairs.
Indoor ramp staircases
A ramp staircase is commonly used in two situations:
- When the stairs lean against a wall
- When there is corner space that can be used
A staircase ramp can be:
- in a straight run, the most commonly used type
- with two flights of stairs connected by a turn; they are often composed by the same number of steps interrupted by an intermediate floor (which will be represented on the floor plan as a rectangle or a square)
- with two straight flights of stairs, connected by winders (that generate a curvilinear path on the floor plan)
- mixed, made by a curved and a straight section
Indoor spiral staircases
Spiral, helical or circular stair type configurations are usually suggested when the staircase is located at the center of the room. There are two types of spiral stairs:
- with one central supporting pillar to which all the radiating steps are attached, also called newel or central pole, fixed to the ground and to the ceiling, with a load-bearing function
- without the central supporting column, when the whole structure is fixed to the ground and to the arrival point.
Spiral staircases are very space efficient, so they are recommended when there are space limitations. In the design floor plans, spiral staircases can be represented by a spiral, a square or a helical layout drawing.
Aspects to consider when choosing a staircase type
- The difference between the two floors to connect: if less than 250 cm, a straight run of stairs can be the solution; if greater than 300 cm, an angled staircase can be used; for greater heights, a staircase with a mid-landing, that interrupts its rise, is recommended
- The space that the staircase will occupy on the floor
- The weight of the staircase and the load bearing structures
- The windows and door layout, and other important elements, that should be left free, in order to avoid obstructions of access routes and entrances
- The position of the staircase: located in the corner, leaning against a wall or situated in the middle of a room.
Internal staircase design, offset
The distance between the last riser of the first ramp and the first riser of the second ramp is defined as offset.
The offset is a ‘structural artifice’ that guarantees a series of advantages (both aesthetic and functional) and a continuity of the handrail. From the aesthetic point of view, the alignment between the intrados of the ramps and the intrados of the landing is ensured by the offset.
The continuity of the handrail inside a staircase in a building is important not only to ensure users’ safety on the staircase, but also because it offers the possibility, in case of disabled people, to mount a stairlift.
In the figure below, the part highlighted in red (consisting of screed + cladding) is equal to half of the riser: the result obtained is just a 0 offset (the last rise of the arrival ramp – riser 1- is perfectly aligned with the first raising of the starting ramp – raising 2).
Factors to consider when designing a staircase
When designing a staircase some factors should be considered:
- All the steps on the same flight must be identical
- Any stairway that has more than 15 steps have to incorporate a landing in between
- The width of each landing must not be less than the width of the ramp
- When possible, use of straight stair flights should be preferred
Width of flights
When deciding the width of the stairs, the maximum number of users that ascend and descend in the same time and the type of use should be considered too.
The width of the stairs, as well as the width of the hallways, shall be dimensioned according to the maximum number of people that could make use of them.
The maximum flow of people shall be calculated in the hypothesis of a contemporary escape/exit of all the persons that live, work, or carry out activities in the building and have access to the stairs and ramps.
In case of public buildings and places open to the public, the width of the stairs in relation to the maximum capacity exit, as well as the most important technical requirements (such as: steepness of stairs, or rise-to-going ratio, flooring characteristics, etc.) are regulated by the national building codes.
For indoor stairs, must have flights with minimum clear widths of 80 cm, in case of spiral stairs the diameter must be at least 110cm. The slope of the stairs must have a pitch angle between 30° and 60°.
Barriers and Railings
Gaps larger than 10 cm between balusters and the handrail must be avoided (vertical and horizontal elements), while the handrail must be set at 90 cm in height from the treads.
To avoid access of small children to stairs or balconies, special wooden or metallic safety gates may be adopted. These kind of gates may have manual, electronic or key-lock opening mechanisms.
Weight carrying capacity
The Weight carrying capacity that a staircase must be able to withhold is 400 kg per square meter.
Steepness – Risers and Treads
While going to design risers and treads, the difference of level should be considered.
Generally, riser heights should be set between 15 and 17 cm (max 20 cm for service stairs), and between 13 and 15 cm for public buildings (hospitals, schools); while the tread depth calculation is related to the users physical effort necessary to overcome the riser’s extension in height.
Usually the Blondel formula is used:
2r + t = 62 ÷ 64 cm
r represents the riser
t represents the tread
For private stairs in dwellings the relationship between riser and tread dimensions can be increased:
2r + t = ÷ 65 (with max value of r = 23 cm)
Usually, a maximum of 15 treads for each flight of stairs should not be exceeded, although, in certain cases, especially for restoration projects, a higher number of treads is suggested instead of having excessively high risers, making stair ramp ascent more comfortable for its users avoiding factors relating to excessive steepness. In conclusion, treads with rounded edges are more practical and safe in case of intense usage.
How to design stairs with a BIM software
Download the 3D BIM model (.edf file format) of the Bifurcated stairs project
Download the IFC model of the Bifurcated stairs project
Download the project layout DWGs of the different types of staircases