A Definitive Professional Guide  for Spiral Staircase Architectural Design

Spiral staircases are highly adaptable designs with daring shapes and different configurations that require careful planning attention. They can also be iconic project objects and great space-savers. Here, we examine different styles and dimensions of a spiral staircase design, also providing a 3D model available for you to download that has been produced with a professional software for architects and engineers.

Spiral staircase: render produced with Edificius

Why chosing a spiral staircase?

The need to optimize spaces is one of the most recurrent requests that technical experts must address in order to deliver creative and at the same time functional solutions. In fact, when designing a staircase, it is crucial to combine aesthetic, functional and structural needs, such as defining the stairs type, shape, material, structure, location and correct layout. They are choices that obviously affect the final quality of a project.

A spiral staircase design guide can help you to better address all these aspects.

For more information on interior stairs planning, see our Focus insight on “How to design a staircase: criteria and examples to download”.

Types of Spiral Staircases and Advantages

The spiral staircase is a particular type of curved ramp staircase more common in private and residential buildings, in small spaces or in special contexts.

Types by Shape

Depending on architectural choices and the configuration of the space in which it must fit, the spiral staircase can have a plan:

• circular;
• square;
• elliptical.

Circular plan | Square plan | Helical plan – spiral staircase produced with Edificius

Circular Spiral Staircase

The circular spiral staircase is the most common type, as it occupies a smaller area than the other types.

Generally, the structure of the spiral staircases consists of a central support post that develops vertically where cantilevered steps are inserted (as in a cantilevered staircase).

You can use a wide variety of materials when building a spiral staircase, however they are usually built in metal or wood or rarely in reinforced concrete in case of outdoor staircases. Steps can be made with any material.

Spiral staircase design – floor plan produced with Edificius

Opting for a spiral staircase rather than a traditional type of staircase (e.g. L-shaped configured with a rectangular plan, etc.) has obvious advantages, especially in terms of space management. A spiral staircase, in fact, occupies a small surface in plan and can also be positioned in stairwells with a diameter of about 1.20 m.

In addition, a wide range of prefabricated solutions are available on the market that also allow significant savings in terms of cost and installation time.

Square Spiral Staircase

The square spiral staircase features a helical development on a square or rectangular plan. In this case, the design of the staircase follows a more geometric trend, with trajectories that approach more closely to straight segments.

Compared to the circular version, it can offer steps with a wider tread in the linear portions, improving the comfort of ascent and descent. The square shape adapts particularly well to buildings with angular floor plans or rational internal layouts, where the geometric rigor of the project requires consistency even in vertical elements.

Aesthetically, it presents itself as a more technical and rigorous solution, often used in modern contexts, offices, showrooms, or public buildings. However, its construction can be more complex and requires careful planning to ensure an adequate balance between functionality and stability.

Elliptical Spiral Staircase

The elliptical spiral staircase represents the most sophisticated and expressive variant. Its development is based on an oval plan, which gives the staircase a fluid yet more dynamic appearance compared to the traditional circular shape.

Thanks to the greater length of the ellipse, this staircase can offer wider and more comfortable steps along the entire path, improving the ergonomics of movement. It is a preferred choice in representative environments, prestigious villas, luxury hotels, or contexts where the staircase is not just a functional element, but becomes the protagonist of the space, almost an architectural sculpture.

However, it should be considered that the elliptical staircase occupies more surface area than the circular one, requires custom design, and generally has higher costs, both due to the construction complexity and the quality of the materials used.

Types by Material

In addition to the shape of the plan, another determining aspect in the design and choice of a spiral staircase is the material with which it is made. The material affects not only the aesthetics but also the stability, the weight of the structure, maintenance, and the final cost.

The most common solutions use:

• metal,
• wood,
• reinforced concrete.

Metal Spiral Staircase

Metal spiral staircases are among the most widespread due to their versatility, the lightness of the structure, and the ease of prefabrication. Made of painted steel, stainless steel, or galvanized iron, they are particularly suited to modern, industrial, or minimalist contexts. They offer great durability over time and can be designed with very thin profiles, ideal for reducing visual bulk. Additionally, metal allows for lightweight and dynamic self-supporting solutions, often combined with glass railings or wooden steps, for a highly sought-after material contrast. They are perfect for indoor environments but, if properly treated, are also widely used in outdoor spaces.

Wooden Spiral Staircase

Wooden spiral staircases are the ideal choice for those who desire a warm, welcoming, and natural environment. Wood, a noble and renewable material, is suitable for both classic and contemporary contexts, depending on the essence used and the finish. Versions in oak, beech, or ash, for example, guarantee robustness and durability, as well as a great variety of colors and textures. The processing of wood also allows for fine shaping of the steps and handrails, making the staircase a piece of furniture in itself. However, compared to metal or concrete, it requires more maintenance, especially in humid environments or those subject to intense wear.

Reinforced Concrete Spiral Staircase

Reinforced concrete spiral staircases represent the most massive and solid solution. They are generally built in situ or prefabricated in elements to be assembled on site. This type is suitable for public buildings, commercial spaces, or large residences where the staircase is integrated into the structure of the building. Reinforced concrete ensures remarkable durability and stability, as well as excellent fire resistance and sound insulation. Aesthetically, it can be left exposed for a brutalist style or finished with plaster, marble cladding, resin, or other materials. Being a heavy and permanent structure, it requires precise planning from the earliest design phases.

Spiral staircase dimensions

To determine the correct dimensions of a comfortable and efficient staircase, it is necessary to correctly evaluate the relationship between riser and tread.

Over the centuries, architectural and ergonomic studies have produced various empirical formulas to suggest an ideal rise / tread relationship and ensure safe use of the staircase.

The most commonly used formula to calculate stairs dimensions is attributed to the architect François Blondel, dating back to 1675. The famous formula is based on the fact that the effort made to lift the foot vertically is equal to twice the effort taken to move it horizontally.

He specified that twice the riser height plus the tread depth equals the step length:

2r + t = 62÷64 cm (25.5 in today’s inches)

where r is the value of the riser and t of the tread.

Graphic application of the Blondel formula

Once the correct relationship between riser and tread has been calculated and they are well proportioned to fit our stride, we need to determine each single value.

For each type of staircase, the tread must not be less than 25 cm. In spiral staircases the triangular shape of the step implies a variable tread from the center of the staircase to the handrail.

Design of a spiral staircase – Section produced with Edificius

The actual tread dimensions for a set of stairs should be calculated considering the path of travel that connects different vertical levels by dividing the height between the levels into manageable steps, after having identified the stairs diameter and 30 cm distance from the handrail. The riser must be calculated keeping in mind the floor-to-floor height, that is the measurement from the top of the pavement floor (extrados) to the ceiling surface (intrados).

In fact, since the spiral staircase wraps around a central post, each step must be at least 2m away from their simmetrical equivalent on the upper module, so as to ensure an adequate level of safety for users passing through.

Design of a spiral staircase – Minimum distance between two equidistant points – produced with Edificius

In small diameter spiral stairs (100/130 cm) where it is not possible to insert more than 12 steps per revolution, otherwise risking reducing the tread depth too much, the value of the riser will tend to be higher than in straight-run stairs.

Spiral staircase design: a practical example

Let’s now take a closer look at a case study that we have prepared to provide a practical example for your spiral staircase design.

Let’s assume that we need to design a circular spiral staircase. Having a floor opening with a diameter of 1.30 m, we need to overcome a height difference of 3.00 m.

It is recommended that the diameter of the floor opening is a few centimetres greater than your stair’s diameter so to easily accommodate body movements. In this case, we have determined the diameter of the stairs to be 1.20 m.

First of all, it is necessary to establish the position and width of the arrival landing and the length and position of the path of travel.

It is advisable that the width of a spiral staircase arrival landing is at least equal to the tread width. For this reason, we have designed an arrival landing with a width equal to the stairs radius (in this case 60 cm). We will thus have an equilateral triangle with internal angles equal to 60°.

For an ideal design, the path of travel should be placed at about 30 cm distance from the handrail. Consequently, for stairs with 1.20 m diameter, we will have a travel path diameter of 0.60 m.

Let’s now calculate the length of the travel path in plan:

0.60 m x π = 1.88 m

to which we need to subtract the space occupied by the arrival landing.

Therefore, the definitive value of the path of travel that can be used for the calculation is 1.88 m – (1.88 / 6) m = 1,57 m.

At this point we can draw an elevation view of the staircase that has been developed in plan view. We can define the path of travel measurement horizontally, that is included between the back and the front landing points (1.57 m) and vertically insert a 2.00m mesurement of the equidistant points on the two staircase modules. By connecting the two ends, we can obtain the actual path of travel equal to 2.54 m (that can be calculated with the Pythagorean theorem).

Next, we can proceed with the calculation of risers and treads.

Finally, we can draw the staircase in plan view to verify a comfortable access and exit from the stairs structure. If the entry point results uncomfortable, we can either rotate the entire staircase, thus also moving the exit point, or change a right-hand to a left-hand stairs direction.

The staircase that we have designed for this case study has a steel structure, with a central post with circular section. The contrasting materials choice, marble and black resin, produces an astonishing final result.

Rendered section of a spiral staircase produced with Edificius

3D BIM model download

Here’s the 3D BIM model of a spiral staircase produced with an architectural BIM design software that you could use as a project example.

Download the 3D BIM model (.edf file) of a spiral staircase project

FAQ on Spiral Staircases

What are the recommended minimum dimensions for a spiral staircase?

The minimum dimensions of a spiral staircase can vary based on the building regulations of the country where it is installed. However, to ensure safety and comfort in daily use, it is recommended:

• a minimum diameter of 150 cm for comfortable use,
• a usable width of the tread of at least 65 cm,
• a usable tread depth of at least 25 cm,
• a clear height above the steps (headroom) of at least 200 cm.

It is always recommended to consult local regulations or a qualified technician, especially in public spaces or where specific safety constraints exist.

What is the most practical diameter for a spiral staircase in residential settings?

The recommended minimum diameter for a frequently used spiral staircase is at least 150 cm, to ensure a comfortable and safe tread. However, for secondary stairs (such as access to lofts, attics, or technical rooms), it is possible to adopt smaller diameters, starting from 100–120 cm, albeit with some compromise on comfort. It is always essential to check the local regulations of the country where the intervention is planned.

How are the rise and tread dimensions calculated in a spiral staircase?

The Blondel formula is often used, an ergonomically recognized reference internationally:
2 x rise + tread = 62 ÷ 64 cm
This formula ensures correct proportions between the steps, adapting the staircase to natural walking patterns.
In a spiral staircase, the tread is triangular and is measured about 30 cm from the handrail. Local regulations may impose minimum or maximum values for rise and tread, so it is important to verify them during the design phase.

How much space is needed to install a spiral staircase?

The space required depends on the diameter of the staircase and the presence of a passage opening (well opening) in the upper floor. Generally, it is recommended that the opening has a diameter at least 10 cm larger than that of the staircase, to allow for easy movement during ascent and descent. In the case study presented in the article, for example, for a staircase with a diameter of 120 cm, an opening in the floor of 130 cm was provided.

How many steps can a spiral staircase have in a complete turn?

Generally, to maintain a comfortable tread, it is recommended to include no more than 12–14 steps for each complete rotation (360°). Exceeding this number can significantly reduce the usable depth of the step. Again, the number of steps may be limited or regulated by local regulations, especially for public-access environments.

What height should the handrail of a spiral staircase be?

The recommended height of the handrail is 85–90 cm measured from the edge of the step (nosing). In some countries, regulations may specify minimum or maximum values, such as 90 cm in Europe or 34–38 inches in the United States. Therefore, it is essential to adapt the design to national rules.

What depth should the step of a spiral staircase have?

In the most frequently used passage points (generally 30 cm from the handrail), the depth of the step should be at least 25 cm. Steps that are too narrow or with rises that are too high reduce safety and comfort of use, especially on stairs with smaller diameters.

What is the minimum width of the usable tread?

To ensure proper usability of the staircase, the minimum width of the usable tread (i.e., the walkable space between the center of the staircase and the handrail) should be at least 65 cm. In contexts where this is not possible (secondary or less frequented stairs), it can be reduced to minimum values of 50–55 cm, provided it complies with local building regulations.