Danish carpenters will learn to build homes with hemp and straw

Straw and seaweed for insulation and hemp blocks instead of aerated concrete. The production of traditional building materials accounts for 10-15 percent of the world's CO₂ emissions. As such, newer, greener ways of building homes are needed to protect our planet's resources and reign in CO₂ emissions.  

Researchers from the University of Copenhagen and Aalborg University are working on a new project that does just that in tandem with Danish vocational school carpentry programmes. Working together, they will shepherd new sustainable building materials and methods into the construction industry within just a few years.

"The construction industry’s green transition needs to be accelerated and carpenters account for the nation's largest group of craftspeople. Their knowledge and professionalism are crucial for the transition to shift up a gear, so it makes perfect sense to begin with them," says Professor Lisbeth Garbrecht Thygesen of the Department of Geosciences and Natural Resource Management, who heads the project.

The researchers will work together with the vocational schools to teach carpentry apprentices how to use so-called biogenic materials like wood, seaweed, reeds, straw and hemp for construction. Besides having less of a carbon footprint than traditional building materials, biogenic materials contain carbon captured from the atmosphere.

"Biogenic materials can convert new buildings into CO₂ storage facilities that can store the same amount of carbon each year as is currently emitted by our annual consumption of concrete alone," says Lisbeth Garbrecht Thygesen.

Sturdy sustainable houses

Among other things, the researchers and carpenters will develop a new type of exterior wall that doesn’t contain concrete or classic insulation material like glass wool or stone wool. Nor will the exterior wall have a plastic vapor barrier for damp proofing. Instead, wood, for example, can be used for external siding, with blocks of pressed hemp, straw or wood fibers being used for insulation.

"We will develop and test several new types of building materials and constructions in close collaboration with vocational school instructors and students to ensure that the solutions are healthy and sturdy, while also making sense in the construction process so that they can be readily adopted by craftspeople," says Lisbeth Garbrecht Thygesen.

The project links research directly with instruction, as the vocational school carpentry apprentices will build their test house using wall elements fitted with measuring devices. In the test house, researchers will be able to collect data and study the effects of different seasons, temperatures and purposes for which the house was built.

Here, moisture in particular will become a focal area. Because there is a big difference between the impact of moisture in a home lived in by a family, for example, versus a warehouse.

"A typical family living in a detached house generates lots of moisture through cooking or showering. This moisture can penetrate the exterior walls and cause mold or rot. We need to avoid this in new exterior wall construction by controlling moisture migration," explains Associate Professor Emil Engelund Thybring of the Department of Geosciences and Natural Resource Management, another project participant.

Science and craftsmanship for faster approval

According to the researchers, one of the major challenges when introducing new home construction methods is that it often takes a considerable amount of time before they are accepted as good building practice and integrated into the Danish construction industry’s “general technical knowledge” (alment teknisk fælleseje), the mark of quality, robust Danish craftsmanship. Achieving this integration is typically an insurance company requirement for them to cover a building.

Therefore, the test house has the important function of being able to far more rapidly demonstrate whether the new materials and construction methods work. Normally, this process can take many years of testing a new method by craftspeople across the country before their experiences are incorporated into new guidelines – or what is professionally known as good building practice and general technical knowledge.

"Instead of the 10 or 20 years that it may take for changes in the way we build houses to take effect, the goal here is to do so in three to four years. During this time, we will develop and test new designs and materials that can be incorporated into the Danish construction industry’s general technical knowledge by combining scientific and craftsmanship approaches," says Emil Engelund Thybring.

The initiative comes at the right time. On the political end, climate requirements for new buildings larger than 1000 square meters are already being introduced in Building Regulations from this year on. These will apply to all new structures from 2025. The requirements will be tightened rapidly after 2025 to get the construction industry to implement a green transition.