Universal and flexible use

In city centers, buildings must meet certain requirements. For example, they should allow mixed use: retail and food service on the ground floor and offices and apartments on the floors above. They should also be easy to adapt for reuse over the long term. Such technical flexibility can be achieved only with point-supported ceilings. Point-supported means that columns support the entire load of the building. Load-bearing intermediate walls are no longer required. This results in a high degree of design freedom in the building design. For example, the walls can be arranged differently on each floor. This is essential for mixed use because retail, food service, offices, and residential areas each require distinct spatial layouts.

Multi-story buildings are constructed primarily using point-supported reinforced concrete ceilings. Hans Jakob Wagner, a scientist at the Institute for Computational Design and Construction (ICD) at the University of Stuttgart, wants to change this. As part of the “Universal Timber Slab” research project, he and a multidisciplinary team are developing a new type of point-supported wooden ceiling slab that eliminates certain design disadvantages. Until now, point-supported wooden ceiling slabs have been made from wood products with fibers that are always in line with each other. “However, the flow of force in a point-supported ceiling slabs curves from all directions toward the column,” explains Wagner. This mismatch greatly weakens current point-supported ceiling slabs.

In order to achieve the required stability, point-supported wooden ceiling slabs have traditionally required large construction heights. This often leads to high costs and considerable amount of material use. Conventional point-supported wooden ceiling slabs are cost-effective only when components are regular rectangles because this minimizes material waste. This simple form is the only economically viable one. However, city centers often require complex geometries such as irregular polygonal floor plans that optimize the use of limited and irregularly shaped plots. Reinforced concrete slabs are preferred in these cases because they can be cast into any shape at a lower cost.  

In order to overcome these technical and economic obstacles, Wagner has designed a new computational planning and digital production process, which uses horizontal glue-laminated timber. During stacking, the wooden boards are bent so that the wood fibers no longer remain straight. They now closely follow the flows of force in the point-supported ceiling. “This makes the entire supporting structure particularly efficient,” says Wagner. “This allows us to build ceiling slabs 30% thinner than conventional laminated timber ceiling slabs and thus save a lot of material.” The method allows the production of irregular polygons tailored to any building plot and thus minimizes material waste. This means that despite complex geometry, their new point-supported wooden ceilings could be more cost-effective than alternative wooden ceiling slabs in the long term.

“Point-supported wooden ceiling slabs can thus also be economically competitive in urban buildings with mixed uses,” says Wagner. “This opens entirely new possibilities for timber construction, which is both more sustainable and better for indoor climate than reinforced concrete.  The method developed in the framework of the “Universal Timber Slab” project also makes buildings more compact. Compared with conventional point-supported timber ceiling slabs, the slimmer design saves 30–70 cm in construction height. As a result, the building’s facade area is reduced by up to 20% while maintaining the same room height.

“Universal Timber Slab” is funded as part of the EIC Pathfinder project (funding period: October 2024 to October 2027). Alongside the project coordinators at ICD (Prof. Achim Menges, Prof.Thomas Wortmann), the collaboration includes the Institute of Building Structures and Structural Design (ITKE) (Prof. Jan Knippers), the Institute for Acoustics and Building Physics (IABP) (Prof. Philip Leistner), and the Institute of Construction Materials IWB (Jun.-Prof. Philippe Grönquist) as well as the Materials Testing Institute (MPA) (Dr. Gerhard Dill-Langer) at the University of Stuttgart. “Universal Timber Slab” is part of the Cluster of Excellence Integrative Computational Design and Construction for Architecture (IntCDC). The research team has applied for a patent for the technology and plans to launch a start-up before the end of the project to bring the method to market maturity.  To this end, Wagner is seeking collaboration with the construction industry.

The EIC Pathfinder is one of the main funding lines from Pillar 3 (Innovative Europe) of the Horizon Europe program launched in 2021. This funding line does not support traditional basic research but rather visionary projects in the early stages of development and thus targets new technologies with the potential to open up new markets.