Newly-developed building material based on traditional cob

‘Reetwellerlehm’ (Reed Cob) 2023-2025

From 2022-2025, the Zentrum für Peripherie developed the building material Reetwellerlehm (Reed Cob) under the direction and based on an idea by Ute Reeh with experts, research institutions and companies. The federal government’s Autobahn GmbH is enabling the construction of two wall segments to investigate their durability in salt spray and the acoustic effect. The aim is a subsequent systematic research project and the implementation of the Brandenburg Alhambra research and pilot project.

Development of a process for reed utilisation from rewetted soils and large-scale cob production

Cob construction is an ancient, traditional solid loam construction technique. The building material cob consists of roughly equal proportions of regenerative raw materials and loam. Straw, heather or other plant fibres take on the function of reinforcement, while the loam acts as a binding filler. The requirements for loam are relatively low, so that local or regional excavated soil can be used in many parts of the world.

Reed was a material traditionally used to cover roofs in northern Germany. Moors, marshes and lake shores produce reeds every year, which can be mowed and utilised. Reeds harvested in Germany are currently hardly utilised at all. Reed utilisation makes it possible to combine economic efficiency and nature conservation. In cob, reed accounts for up to 10 % of the dry weight and up to 90 % of the volume.

Reed cob is a modernised version of cob. With mechanisation and automation, reed cob is suitable as an affordable building material for contemporary architecture and construction technology that meets the requirements of climate change and is more adequate than concrete for certain purposes.

The intention and goal is to transfer the traditional cob construction method using loamy excavated soil and straw into a modern construction technique. This is done on the basis of the newly developed “Reetwellerlehm” and by development of an efflcient arge-scale production process.

The key is the moorland-friendly management of re-wetted soil by means of reed harvesting and the utilisation of the reed for the production of prefabricated Reetwellerlehm (Reed Cob) elements. This creates the conditions for the development of new value chains. Reed serves as a reinforcement for the loam and binds carbon during the useful life of the building material. Regionally or locally produced Reed Cob is ‘upturned’ nature conservation in the broadest sense; it binds carbon (CO2 sink); offers habitat potential for wild bees and other protected species; is sound-insulating, heat-insulating, sound-absorbing (rooms without reverberation), moisture-regulating, fully recyclable and microclimatically balancing.

The reed cut, which is relevant for the CO2 sequestration of rewetted soils, opens up new economic prospects for agriculture. Reed Cob as a building material makes it possible to combine economic efficiency, climate resilience and nature conservation.

Public pilot buildings will enable visitors to form their own impression through their own observation and experience.

Reetwellerlehm is

  • a contribution to climate protection and a revolutbon in building technique
  • a sound-absorbing, heat-insulating, indoor climate-regulating, fully recyclable, CO2-binding building material for noise barriers, load-bearing walls, façades; acoustic walls in interiors
  • vertical nature conservation surfaces
  • a habitat for wild bees
  • a sustainable economic development
  • a sales market for reed

Research method

  • Utilisation of the conflict between infrastructure / building construction and nature conservation / preservation of biodiversity as a starting point for innovation
  • Transdisciplinary, appreciative teamwork as a prerequisite for high quality
  • Practice and theory going hand in hand
  • Iterative process management
  • Parallel development of the results and the structure and dynamics of the research process itself

Research goals

  • Creation of a guideline for the maintenance of re-wetted soils including the logistics for harvesting, processing and marketing of reed
  • Analysing the ecosystem function of thatched loam
  • Determination and evaluation of biodiversity on sample walls
  • Classification as a compensatory measure
  • Systematic analysis of the structural properties of Reetwellerlehm
  • Integration into regulations and standards
  • Design and construction of a plant for the large-scale production of thatched loam as an affordable building material

Network and research partners for Reetwellerlehm

  • Federal Institute for Materials Research and Testing BAM (structural investigations and analyses)
  • Federal Highway Research Institute BASt (acoustic measurements, reuse of removed soils)
  • Elbe-Brandenburg River Landscape Biosphere Reserve (consulting and monitoring)
  • Bosch & Partner GmbH (investigation and evaluation as an ecological compensation measure)
  • Lehmbaustoffe Schleusner & Söhne GmbH, Schönhausen Elbe (large-scale production)
  • SNW Ingenieure Berlin (structural engineering, statics and foundations)
  • Uwe Prochnow and Seegemeinde Boberow (harvesting technology and logistics, perspective of agriculture and landowners)
  • Zentrum für Peripherie (idea generation, material development and process control)

Reetweller test specimen for measuring sound absorption in the impedance tube by the Federal Highway Research Institute (BASt)