Constructing with flax, reed, straw, algae, bamboo and elephant grass

written by Willem Böttger
Professor Biobased Building at the Centre of Expertise Biobased E

Centuries ago man lived a sober life, using energy sources such as wood and peat to heat their houses and animal oils to create light. The houses were made of stone, wood or loam and insulated with sod, straw and wool.

With the active extraction of coal and later of oil and gas, living conditions improved considerably. The cheap fossil energy sources also ensured that we developed special materials, such as mineral wool as an insulation material and carbon composites for strong and light structures. The downside is that the economic growth, based on the increasing use of fossil fuels, has become synonymous with global warming, depletion of scarce natural materials and increasing environmental pollution.

To combat climate change, buildings have become insulated, but with insulation materials that require much more energy to produce them, so that the climate is more affected instead of less. And due to insulation, the indoor climate in homes has become worse. And this bad indoor climate affects us more because we live much more indoors than in the old days.

Impact for the construction industry

If we want to design a construction product or an entire house, we are dealing with properties and preconditions from production, material, design and market. If we want to construct a bridge and we have only wood available, we will design a different bridge than if we have stones available. If we have wood but no saw, we will design a different bridge than if we have a saw. Material, production techniques and design influence each other, give each other degrees of freedom and limitations.

By working with biobased materials, the production techniques, design and the market can and must innovate. This means a broad-minded approach from the lectorate and close cooperation with other lectorate groups, universities of applied sciences and research universities.

Historically, an architect would draw a building and the contractor would seek the material to build it. As materials and the circular process are becoming more important, the roles of architects, contractors and producers are changing. They need to learn more from each other’s field of expertise in order to achieve optimum results. The teachers and students of HZ have to adopt to this changing role.

Choice of material

The lectorate focuses on local Zeeland and West Brabant raw materials:

  • Bio-composites are made from natural fibres such as flax and hemp, combined with a (partially) organic resin. Together they form a strong, stiff and light construction material.
  • During the growth of fungi on fibrous and nutritious residual materials from agriculture, a dense network of mycelium is formed. Depending on the type of mycelium, fibre and food and the pressure, the materials can be hard, but also rubbery.
  • With hemp lime (hempcrete), a mixture of lime and the woody parts of the hemp stem (the shives), external walls, other walls and even roofs are insulated. Hemp lime has a moisture-regulating effect, creating a comfortable and healthy indoor climate.
  • Flax, reed, straw, algae, bamboo and elephant grass are local, insulating, moisture-regulating and sustainable products, with their own market dynamics. The lectorate is investigating locally produced bamboo.

Circular biobased economy

To reverse the growth in the use of fossil fuels and scarce natural materials, climate change and environmental pollution (indoors and outdoors), the government has decided to develop a circular biobased economy up to the year 2050.

The Biobased Building lectorate was established in this context. The lectorate is part of the Centre of Expertise Biobased Economy, a collaboration between Avans University of Applied Sciences and HZ.

Added values
The ‘biobased’ property is not in itself a key to success. In addition to claimed environmental benefits, technical and economic benefits are also needed to replace conventional building materials. We will summarize these benefits under the concept of added value. We distinguish six forms of added value.1. Strong, stiff and lightBiobased materials naturally have a low density. This allows you to make light constructions with strong and rigid materials such as bamboo, wood and flax composite. This makes bio-composites an interesting material for lightweight bridges and vehicles.2. Vibration reduction and noise reductionResearch from Ghent University¹ shows that flax composite has seven times stronger vibration absorption than carbon composite. Research by the lectorate shows that biobased materials have better sound absorption than many conventional ones. 3. AntibacterialVarious studies² ³ show that some biobased materials, such as wood and hemp, have an antibacterial function. This can be of added value in minimizing disease transmission through, for example, the handles of doors.4. Thermohygric: heat and moisture absorbingBiobased materials are used in a vapour-open insulation system that regulates the humidity of the indoor climate. This has advantages when it comes to comfort, the prevention of condensation and mould and the service life of the construction.5. Environmental impactBiobased materials have a very low CO2 footprint. Until now, the government focused on saving energy during the usage phase of a building, but by also minimizing the production energy of the materials, a real step can be taken.6. Unique, form-free, natural appearanceWith biobased materials, often different production processes and processing methods apply than with traditional materials. This also creates space for new architectural forms and appearances.

1) Study of the damping and vibration behavior of flax-carbon composite bicycle racing frames, Joachim Vanwalleghem, Werktuigkunde-Elektrotechniek, 2010 Universiteit Gent.
Survival of extended-spectrum β-lactamase-producing Escherichia coli on thirteen different biobased materials, an in vitro experiment, Stefan Rentier, Amphia Hospital Molengracht Breda | Laboratory for Microbiology and Infection Control Augustus 2016, Avans Hogeschool.
3) Antibacterial Properties of Hemp and Other Natural Fibre Plants: A Review. B. A. Khan, P. Warner and H. Wang. 2, Toowoomba : BioResources, 2014,
Vol. 9

Pictures: Orio Architecten, Ulrike Bött