Holz-Lehm-Hybrid

The Holz-Lehm-Hybrid [HLH] project (in English “Timber-Earth-Hybrid”) investigates novel nature-based building components and techniques in the context of a demonstration building project in Berlin.

In recent years, theoretical ideas for the transformation of the building sector towards regenerative practices have increasingly been translated into real-world construction projects. In particular, construction with timber has emerged as a crucial pillar of this transformation. The forestry and timber industries have taken initial steps towards models of sustainable and regional processing, and planners are acquiring relevant competencies to design and execute timber construction at scales ranging from demonstration projects to high-rise buildings. HLH focuses on simplified construction techniques, possibilities for further minimizing the environmental costs of construction, and the performance of regenerative building components beyond wood.

As part of the redevelopment and expansion of an office building in Berlin-Weißensee, the project is designed as a living lab that prototypes and monitors regenerative building components at the building scale. This includes: recycled concrete slab foundations, timber floor slabs, timber fire walls, load-bearing earth block masonry, timber-earth-hybrid ceilings. All components follow the common goals of: the highest possible regionality of resources, a minimum use of primary energy and materials, and optimized dismantling and reuse possibilities. For more details on each of these components, scroll down to "Expected outputs".

The project is a collaboration of Bauhaus Earth (research lead), B&O Bau (developers), Sauerbruch Hutton (architects), the Industrieverband Lehmbaustoffe e.V (IV-Lehm), and the Landesbeirat Holz Berlin-Brandenburg (LB Holz BB). It is funded by the Deutsche Bundesstiftung Umwelt (DBU).

Next to testing and monitoring, the HLH project aims for a comprehensive documentation and communication of the research findings. These will be made available through online publications and a permanent exhibition. Training opportunities, showcases, and conferences will take place throughout the project. Stay in the loop by following us on LinkedIn.

The following components will be prototyped, realized, and monitored:

I. Reused Concrete Slab Foundation

The foundations of buildings often incur the highest CO₂ footprint, primarily due to the utilization of energy-intensive materials such as concrete and steel. These materials are needed to meet the high requirements for moisture sensitivity and load-bearing capacity. The HLH project aims to repurpose the existing building's foundation slab for the new construction. The foundation slab will be cut on site and reused as a stacked point and strip foundation for the new building. This approach minimizes the use of concrete and the amount of waste generated by the partial demolition. One of the main analyses of this in-situ reuse is the detailed consideration of the costs and their comparison with the costs of the conventional construction sequence of demolition and new construction.

II. Timber Floor Slabs

To demonstate the use of renewable resources, the floor slab will be constructed from timber. To avoid a conventional reinforced concrete floor slab, this requires innovative changes in design and manufacturing of the component. Special attention will be placed on the use of regional pine wood. The floor slab will be executed as an insulated timber beam construction, similar to a typical timber frame exterior wall, over a crawl space. Monitoring will involve measuring moisture levels in the crawlspace, floor slab, and rooms above to determine if the airflow is adequate to prevent moisture damage.

III. Timber Fire Walls

Despite strict fire protection regulations in construction, it is possible to construct fire walls from timber. The project aims to create a fire wall adjacent to the neighbouring buildings from regional pine wood. The assembly includes visible wood, avoiding additional mineral materials such as plasterboard, thereby increasing the potential for dismantling, recycling, and carbon storage. Pine wood is currently less used in construction in Germany due to higher emissions of volatile organic compounds (VOCs). The project will monitor VOCs to assess the indoor air quality achieved in rooms with solid pine wood elements.

IV. Load-Bearing Earth Block Masonry

The project will be one of the first in Germany to pioneer load-bearing earth block construction. Two-storey earth block walls will be executed as load-bearing components at two locations in the building. By considering earth as a load-bearing material, the project demonstrates that, in addition to wood, other local building materials are up to this challenge. Earth complements wood with its high thermal mass and breathability, addressing weaknesses in timber construction, which can be deficient in sound insulation and fire resistance. Relative indoor humidity will be continuously monitored at various stations to assess the added value of rooms with adjacent visible earth brickwork compared to earth-free spaces.

V. Wood Earth Hybrid Ceilings

The ceiling construction will utilize a timber-earth hybrid ceiling, a component not yet widely applied in Germany. This entails efficiently and appropriately combining both building materials to address the high spans of timber construction with the high mass of earth. In timber construction, the lack of mass in floor slabs often poses a problem for sound insulation. By combining the two materials within a ceiling structure, sound insulation and high indoor air quality can be improved. The project will monitor and evaluate the ceiling's contribution to indoor air and acoustics and track its structural stability.

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