School projects in Berlin with prefabricated wooden modules

School projects in Berlin with prefabricated wooden modules

As a part of Berlin’s school construction offensive, 32 wooden schools were commissioned to be built. The reduction of the construction time to less than half has convinced the Berlin Senate Administration of the use of innovative and sustainable timber modular construction methods. The module structures were built with 8-metre long GLVL beams (made of Kerto® LVL S-beam).

The modular school projects in Berlin were built by the Austrian prefabrication constructor Kaufmann Bausysteme (KBS). To keep construction time short, the three-storey school buildings were constructed from prefabricated volumetric modules. The assembly of the modules took place in Berlin. Due to the short distance to the construction site, the transport was efficient and avoided unnecessary costs. Every classroom is composed of 2–3 modules. The modules were built using CLT load-bearing walls. Two Kerto GLVL beams carry the loads to the walls of modules, allowing a column-free floor plan to be used. The span of these 8-m long beams could not be realised with glulam.

Strong Kerto GLVL beams

Sebastian Hagspiel, Project Manager from Kaufmann Bausysteme, describes the material selection of the GLVL beams as follows: "We are wood builders, not steel builders. Therefore, steel beams were out of the question for us and a stronger alternative to glulam had to be found. These requirements could only be solved by using a material that does not have any weak points such as knots in the cross-sections. In the end, only laminated veneer lumber (LVL) could meet this requirement. There were two materials that came into question: hardwood LVL made of beech and softwood LVL made of coniferous wood."

Long-span beams

For structural requirements, the project partners set out to find a wood-based material with high compression and flexural strength. In addition, the material had to be easy to machine. Bullinger Holzwerke in Germany proposed GLVL (Glued-LVL) as a solution. This product is made from Kerto LVL lamellas glued together to form a GLVL beam. The GLVL manufacturing process was developed by Bullinger in cooperation with Metsä Wood.

Production manager Ingo Faller describes the process as efficient: "We have updated our standard glulam process so that we can use also LVL lamellas. The GLVL beams have high bending strength. It is roughly similar to GL 50. Standard glulam generally reaches a strength of up to GL 30/32." Interestingly, both glulam and LVL are stronger in strength-to-weight ratio than steel. In addition to the technical implementation in terms of gluing, Bullinger paid particular attention to the visual appearance of the beams. Due to the stacked Kerto LVL lamellas, there are no disturbing knots. Thus, the beams have a natural, yet at the same time technical appearance while retaining a very calm and homogeneous appearance.

Easy processing – no special machines required

Both Bullinger and Kaufmann Bausysteme describe the processing of the GLVL beams as very simple. "There is hardly any difference in processing GLVL and standard glulam beams. We were able to use the same tools and fasteners for joinery and assembling the modules that we use for glulam beams", says Sebastian Hagspiel, the project manager for the modular schools from Kaufmann Bausysteme. Unlike hardwood-based GLVL made from beech, for example, the processing of softwood GLVL is very simple and easy.

The main difference between hardwood LVL from beech and softwood GLVL is related to density. The stress on the tools during processing GLVL is similar to glulam. Especially in modular construction, this shortens the assembly time significantly.

Smooth cooperation of the project partners

All project partners agreed to use Kerto GLVL. The architects, structural engineers, owners, and general contractors were all convinced by the material's appearance and performance. "We had to solve some technical challenges in the production of the GLVL in this project. Together with our supplier Metsä Wood, we ultimately succeeded very well. We are ready to deliver products for the upcoming projects with GLVL," says Ingo Faller from Holzwerke Bullinger.

Fire resistance of  Kerto GLVL comparable to glulam

The fire behaviour of the GLVL beams is similar to glulam. The decision to use GLVL was ultimately based on the load-bearing requirements of the modular construction, the 8-m span, and the feasibility of gluing by Holzwerke Bullinger. "The three-storey school building falls into building class 3," explains Sebastian Hagspiel from Kaufmann Bausysteme. Due to GLVL's excellent fire behaviour, the project partners found it very easy to switch from glulam to Kerto GLVL. No additional fire protection requirements had to be met.

Offsite construction shortens the construction time 

The GLVL beams were delivered to Kaufmann Bausysteme for the project with a very high degree of prefabrication. Both the CNC cutting of the beams and the installation of the steel connectors and bearing support reinforcements were already added at Bullinger's factory. The assembly of the GLVL with the CLT walls and finalising the modules took place close to the construction site at Kaufmann Bausysteme in Berlin. The prefabricated modules were assembled in a very short time. Kaufmann Bausysteme's experience with the GLVL beams has been very good. Sebastian Hagspiel from Kaufmann is convinced of the economic benefits and easy processing of GLVL, and plans to use this high-performance wood material in future projects."