The STEP2 unit combines new digital design and fabrication technologies with innovative materials and a comprehensive energy and thermal comfort concept. The ultimate goal is to develop market-ready solutions that allow a sustainable use of energy and resources.

Numerous industry and research partners worked together in an open innovation approach to realize the two-storey unit. The initiative for the unit was provided by main partner BASF.


These are the central innovation objects of the unit:


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The innovation objects in the STEP2 unit

As symbolic building spines, stairs have a significant functional, aesthetic and representational role in architectural spaces. However, bespoke concrete stairs pose significant fabrication challenges when it comes to conventional formwork solutions. To address and minimize these challenges, the innovation object is a complex free-form concrete stair based on research in 3D-printed formworks. In this context, a streamlined digital design-to-production framework is established, enabled through the synergy between computational design and additive manufacturing. The vision is to broaden the design possibilities of concrete stairs and reduce the extra cost, material waste, and labor associated with customization and complexity.

In terms of architectural expression, new design opportunities with highly articulated qualities are built in concrete. Glossy or anti-slip surfaces, ornamental features, and functional conduits are integrated in the design and parametrically controlled. Beyond a radical new design, the stair also integrates features for human comfort and safety.

Ultra-high-performance fiber-reinforced concrete is used for its excellent structural properties that enable very thin, complex shapes, otherwise impossible with regular reinforced concrete. Even though the innovation object is perceived as one coherent sculptural element, it is discretized into individual steps. The lightweight and structurally efficient elements are prefabricated and assembled on-site. The assembly is enabled by a state-of-the-art shape memory alloy post-tensioning system that provides the necessary reinforcement.

The aim is to highlight the benefits of digital tools, not only for the fabrication of bespoke concrete stairs, but for architecture, engineering, and the construction industry in general. Embedded in research, the innovation object demonstrates that digital fabrication technologies are already a sustainable fabrication strategy for context-specific, efficient and performant design solutions. It offers a ready-to-use solution for individual designs and building tasks.

Partners: Digital Building Technologies - ETH Zurich, ROK, BASF Forward AM, New Digital Craft, SW Umwelttechnik, WaltGalmarini, re-fer

The floor slab of the STEP2 unit drives innovations in the NEST focus areas industrial and digital fabrication and energy systems.

3D printing technology offers an enormous potential for the construction industry. It combines the efficiency of non-standard industrial manufacturing with the design and engineering capabilities of new digital design tools. An important application focus for this approach lies on floor slabs for high-rise office buildings. In a preliminary study, an overall technical concept for a ribbed filigree slab was therefore developed in cooperation with architects and civil engineers. This concept can cover spans of up to 14 meters – while at the same time minimizing material usage. A business case analysis evaluated the marketability and made this concept transparent for potential industrial partners.

The floor slab is prefabricated by NEST partner Stahlton Bauteile AG. 3D-printed formwork elements are used to produce biaxially pre-stressed precast elements with integrated beams. Pretensioning significantly increases both the freedom of design and the erection span extending the possible application field to a wide range. Technical functional components are already integrated at the factory.

At the construction site, the elements provided with shear and connection reinforcement are placed on the columns by a crane and completed with mesh reinforcement for the upper reinforcement layer. The in-situ concrete is then applied – the result is a monolithic reinforced concrete slab with beams and material-efficiently thinned out in intermediate areas. The prefabricated slab elements function as lost formwork with defined surface quality.

To optimize the room acoustics, innovative acoustics boxes are integrated into the slab. These were developed in close cooperation between ROK, Stahlton Bauteile AG, BASF and BASF Forward AM. On the lower side of the box there are holes that form the transition to the slab. This creates a perforation in the ceiling elements through which the sound is absorbed. The interior of the box consists of a mineral absorber foam from BASF, which has better sound absorption in the mid-frequency range than conventional sound absorbers.

NEST partner ROK developed specialized digital parametric design tools for the design of the ribbed filigree slab. These tools provide the architect with a great degree of freedom of design in order to accommodate customer requirements. On the other hand, these tools allow very efficient optimization of technical and economic criteria such as material usage, supporting structure and integrated additional functions. In STEP2, some of such optimization criteria were the deployment of recycled concrete as well as the direct integration of acoustic absorption elements.

During operation, the floor slab serves as a thermal storage mass. NEST partner WaltGalmarini AG dimensioned this thermal mass within the context of a holistic, integrated energy and building physics concept for the entire unit. This concept relies on passive technologies to further reduce the energy consumption.

Partners: BASF, ROK, Stahlton Bauteile AG, WaltGalmarini AG

The building envelope plays a central role in the energy performance and comfort of a building. The façade of the STEP2 unit will therefore serve as a development and testing platform for NEST partners and their innovation topics. Its design allows the replacement of certain façade modules with minimal effort.

The NEST partner Aepli Metallbau AG will carry out the development and production planning, the manufacturing as well as the assembly of the façade. The following innovation topics with the responsible partners are planned for the initial operation:

  • AAC façade modules with controlled air supply and integrated shading system. Partner: Aepli Metallbau AG
  • Automated ventilation flaps as a central component of the unit-specific energy and ventilation concept. Partner: WaltGalmarini AG
  • Glazing systems with 3D-printed shading inserts individually adapted to the path of the sun. Partner: New Digital Craft

A core topic of the façade is the shading system. Using different approaches, the project team will analyze functionality, effectiveness and durability of new shading systems and materials and evaluate their influence on the energy concept.

The modular façade design allows the offsite installation of completely new shading systems into façade modules under controlled factory conditions. These façade modules allow for an easy and straightforward on-site installation.

The shading systems are supplemented by innovative glazing systems that affect the light and energy input into the building. Specially developed materials and 3D printing processes are used in some cases to customize the glazing to the site conditions.

Another focus lies on energy production. The façade plays a significant role in the building's energy balance. This research field foresees a set of PV technologies to be subject to efficiency and profitability investigations. During operation, the unit will also provide valuable data about effective user behavior.

The modular construction of the façade as a test and evaluation platform allows the integration of further partners and topics during the operation of the unit.

Partners: Aepli Metallbau AG, WaltGalmarini AG, New Digital Craft

Building envelopes are the essential construction element when it comes to ensuring a comfortable indoor climate, preventing structural damage and reducing energy, operating and investment costs. The development of facades towards optimal energy efficiency with high comfort requirements is complex and therefore a central element of the STEP2 unit. For this purpose, NEST partner WaltGalmarini AG developed a comprehensive energy and building physics concept for the unit.

The planning project started with comprehensive studies of the location, the environment, the intended use and the local climate. Using thermodynamic simulations, control strategies for an adaptive building envelope were developed, which keep room conditions within the thermal comfort range.

The energy concept uses only passive systems such as natural ventilation and lighting, passive heating and cooling to condition the building interior. Active systems will serve only as a supplement if the passive systems do not sufficiently meet the desired comfort requirements. In the STEP2 unit the following technologies, among others, will be validated:

  • High thermal insulation glazing with high spectral selectivity
  • Controlled, natural ventilation by using automated ventilation flaps
  • Adaptive sun protection systems
  • An exposed concrete ceiling that can be activated as an extra storage system for thermal energy. By means of integrated heating/cooling loops, this can be additionally activated if required.

Partner: WaltGalmarini AG

New innovative materials are the key to sustainability. Customized profiles of properties reduce the consumption of resources and energy in their production and application. This makes them a central component of the growing circular economy, which is a key topic of the STEP2 unit.

BASF is contributing its in-depth expertise in a wide range of materials to the project. This includes structural and functional materials, bio-based and biodegradable products, dispersions, additives, coatings, composites, hybrids and multimaterials. With this expertise, the company develops new material systems, formulations and applications, which are further developed with cooperation partners. BASF is implementing a number of innovations in the STEP2 unit:

The light resistance of materials plays a decisive role, especially in outdoor applications. This is why the new UV absorber Tinuvin® 1600 is used in the transparent balcony railing with integrated light design based on polycarbonate.  

Thermal insulation is crucial for the energy efficiency of a building. New mineral-based insulation materials such as Cavipor® or high-performance insulation materials such as Slentex® are considerably expanding the range of applications, offer advantages in processing and recyclability and are also non-combustible. Slentex® has significantly improved thermal transmittance compared to conventional systems. This allows the construction of very thin thermal insulation systems.

The recycling of raw materials is also at the center of the STEP2 unit's materials. Based on the principles of upcycling, BASF and its partners have developed processes to create high-performance surface coverings from waste materials.

In the kitchen area, coffee grounds are combined with BASF's innovative water-based Acrodur® binder to produce durable, high-quality furniture surfaces. High-performance flooring made from textile waste is used for the hollow floor construction. The floor panels, based on recycled denim fibers, are made using BASF's innovative Acronal® resin binder and high-performance coatings. In addition, for the first time in a wood hybrid application, the non-combustible and very high performance insulating material Cavipor® is used for leveling and thermal and acoustic insulation of the subfloor.

The innovative water-based dispersion acForm® is the foundation of a new manufacturing technology with a high degree of wood utilization for three-dimensionally formed wood fiberboards. Due to their thermoplastic moldability, these wood composites are perfectly suited for molding and embossing technologies. They offer completely new design dimensions for furniture and interior design, for example molded furniture, wall and ceiling panels, doors, room dividers or structured floor coverings.

In the field of digital production technologies, BASF also contributes innovative materials, for example synthetic filaments for 3D printing processes such as the Ultrafuse® product portfolio. This comprises a wide range of materials that offer a variety of beneficial properties such as printability, dimensional stability, durability and flexibility.

Such products and processes are used in material- and energy-efficient engineering applications, such as the production of customized formwork solutions for material- and function-optimized prefabricated concrete elements (e.g. weight-optimized spiral staircases), as well as 3D-printed window inserts for daylight control. From design to production, completely digital processes are used, which make optimal use of the synergies between computational design and additive manufacturing.

Partner: BASF

The unit, which will be equipped with new, sustainable materials, some of which are 3D-molded, shall be appropriately illuminated day and night. The artificial lighting solution will be just as innovative and sustainable as all the other elements. The focus of the artificial lighting solution lies always on people and their visual, emotional and biological demands on light. The architecture follows in second place. Lighting requirements vary depending on the activity, time of day, emotional or biological state. This requires not only a spectral adjustment, but also the light distribution must be taken into account. The goal for the STEP2 unit is therefore the development and implementation of a holistic lighting concept that supports the health, well-being and performance of the users in a targeted and long-term manner. The architecturally incorporated, integrative lighting represents an interplay of daylight and daylight supplementation up to artificial lighting at night and is adapted to the use-specific room applications.

Miniaturized systems save material and design components are dispensed with entirely. To avoid scattered light, only highly transparent or reflective optics are used. The light is directed to where it is needed. This saves energy. With the latest reflector technology RFO from Bartenbach, the optics can be reduced to a diameter of 13mm. With an optical efficiency of more than 80 percent, walls are illuminated homogeneously and completely glare-free. The color mixing of the different LEDs is achieved only via the reflector and without a mixing chamber.

The perforated beam lens (LFO), patented by Bartenbach, with a light emission area of 8mm diameter is also being further developed in this project. For the first time, tunable light from 2200K-5000K with up to 850lm is emitted from a single point. This corresponds to the luminous flux of a 60W light bulb (free-radiating) but requires only 14 percent of its energy.

Partners: Bartenbach GmbH, ROK, Stahlton Bauteile AG, BASF

STEP2 Partners

Project Credits: Bespoke Stair

Stair design: Digital Building Technologies - ETH Zurich, ROK Architects
Fabrication System: Digital Building Technologies - ETH Zurich, SW Umwelttechnik
Formwork Development and 3D Printing: Digital Building Technologies - ETH Zurich, BASF Forward AM, New Digital Craft
Structural Design: WaltGalmarini
Precast Concrete: SW Umwelttechnik
Post-tensioning System: re-fer
Project Management: ROK Architects

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