A material of the future?
Conventional construction methods contribute significantly to global CO₂ emissions. One possible sustainable alternative is hempcrete, which is made from the woody core of the hemp plant. A research project at the Technical University of Cologne is focussing on this special building material.
For years, the construction industry has been searching for sustainable building materials. Conventional construction methods, often reliant on concrete and steel, contribute significantly to global CO₂ emissions. In an earlier article on this blog we already wrote about one possible sustainable alternative - Hempcrete.
Luisa Pfau
Hempcrete is made from the woody core of the hemp plant and mixed with a lime-based binder. It offers many positive properties such as excellent insulation, moisture regulation and fire resistance. However, its mechanical properties, such as its low compressive strength, have so far prevented it from being used in load-bearing constructions, which is why it is currently often used for non-load-bearing applications such as wall insulation and infill in timber frame constructions.
A research project at the Technical University of Cologne (TH Köln) entitled "Einfach Mauern mit Hanfkalk" ("Simple masonry with hempcrete") aims to change this by developing and producing hempcrete blocks that can be used in single-layer masonry and are capable of supporting multi-storey buildings, reducing the need for additional materials or structural elements such as concrete or steel.
The TH Köln research team, supported by funding from the German Federal Ministry for Education and Research (BMBF), is investigating how selective densification could improve the material’s structural integrity.
Luisa Pfau
The initiative brings together researchers from multiple disciplines, including architecture, civil engineering, and mechanical engineering. Research associate Jonathan Lunkenheimer works together with Prof. Dr. Arne Künstler from the Faculty of Architecture, alongside Prof. Dr. Björn Siebert (civil engineering) and Prof. Dr. Peter Erdmann (mechanical engineering), the project involves students developing both the blocks and the machinery required for their production.
Advantages of hempcrete blocks
If the project succeeds, the construction sector could gain access to a material that combines sustainability with functionality. The advantages of hempcrete blocks include:
- Carbon sequestration: Hemp absorbs more CO₂ during its growth than is emitted during production, resulting in a carbon-negative material.
- Thermal regulation: With a low thermal conductivity, hempcrete walls of 30 cm thickness require no additional insulation.
- Moisture control: The material is breathable, reducing the risk of damp and mould.
- Fire resistance: Unlike timber, hempcrete does not burn easily, adding to building safety.
- End-of-life sustainability: When demolished, hempcrete can be crushed and returned to the soil as a natural fertiliser.
- Practical handling: Due to the nature of the outer layers of the blocks, cable or pipe penetrations can easily be cut in and sealed with the same residual materials after the respective elements have been laid.
The research teams at TH Köln are trying to determine the optimum mixture of hemp, lime and other biomass and mineral binders, as well as developing a press prototype to test the feasibility of mass producing the compacted blocks. The working process includes targeted densification in certain zones of the blocks to improve load-bearing capacity while maintaining the breathability and insulation benefits of traditional hempcrete.
This involves cooperation with the University of Bonn, which is supporting the project with so-called miscanthus grass, as this is said to have potentially better properties than hemp for these particularly dense load-bearing zones.
Initial trials have already yielded promising results, with wall modules planned for real-world testing. These will assess not only load-bearing capacity but also compatibility with existing construction techniques. If successful, hempcrete could become a viable alternative to aerated concrete or lightweight hollow bricks, offering a sustainable solution for new housing projects.
Outlook
Despite its many benefits, a key challenge is that the supply chain for hemp-based building materials is still underdeveloped in many countries. The research project hopes to overcome these limitations by improving production efficiency and demonstrating the economic viability of hempcrete blocks.
Luisa Pfau
With growing political and environmental pressure to reduce emissions in the construction sector, materials like hempcrete are gaining attention. If the TH Köln project delivers on its promise, the future of sustainable building may be closer than previously thought—one hemp block at a time.