In large timber construction projects, builders often concrete staircases when not much is visible on the construction site except the basement. Carpenters then assemble the prefabricated wooden components.

Timbatec has reversed this sequence: The timber construction is erected, then the liquid concrete is poured in - or we do without concrete altogether and design the staircases from wood. The reversal of the work steps is the logical consequence of today's working methods, because timber constructors calculate with smaller tolerances than concrete constructors. The wooden elements are prefabricated with millimeter precision. This accuracy is not possible when concreting on the construction site. That is why we plan the concreting of the lift shaft as the last piece of the puzzle.

2-D and 3-D representation of the subsequently concreted staircase core: The number of necessary connectors and the thickness of the concrete wall can be reduced thanks to this method.

Less steel and concrete needed

The advantages of the new approach are obvious: significantly fewer steel profiles and screws are needed, the connection from the timber structure to the concrete core is simpler, and the construction time is shorter. The erection and dismantling of the scaffolding and formwork for the concrete core is no longer necessary and the quantity of concrete used can be reduced. This is achieved with the same performance: the subsequently poured concrete is positively and non-positively connected to the wooden structure. The stairway cores serve as static bracing for the buildings and ensure escape routes in the event of fire.

Timbatec developed the efficient and resource-saving method with the subsequently concreted staircase cores in 2019 for Haus Krokodil in Winterthur, a timber building with 248 apartments. Since then, it has been applied to a large number of multi-storey timber buildings.

Staircases stairwells and elevator shafts can also be constructed without concrete. This also applies to safety stairwells, for example in hospitals or high-rise buildings.

Buildings with a total height of more than 30 meters are considered high-rise buildings in Switzerland. By law, such buildings must be built with safety stairwells. This means that all vertical escape routes must be specially protected against the ingress of smoke and fire. If access for the fire department is impossible in the event of a fire, buildings under 30 meters high must also be planned with a safety stairwell. The same applies to hospitals.

Until now, such stairwells and escape routes were always built in concrete. The fact that safety stairwells are now possible in timber construction is demonstrated by the apartment building on Albulastrasse in Zurich: Here, the stairwell was constructed with cross-laminated timber and enclosed with 18-millimeter-thick gypsum fiberboard - encapsulated, as experts call it.

Two minutes' walk from Zurich Altstetten station is an apartment building with over 30 apartments on seven floors. Since the tight space conditions do not allow access for the fire department everywhere, Timbatec's engineers planned a safety stairwell - made of wood.