Building structures with more biogenic materials

Published: 27.02.24

We need more climate and environmentally friendly solutions in construction. Therefore, DBI is involved in a new project to develop and fire-test prefabricated structures in biogenic materials scaled for multi-storey construction.

Wood has been identified as a CO2-reducing building material, and is gaining more and more ground in construction. But wood is a limited resource, which is why we should also look for more easily accessible materials – such as straw. However, these kinds of materials are quite combustible and therefore require a special focus on material composition and production conditions in order to be fireproof to build with.

On this basis, in collaboration with CINARK at the Royal Danish Academy, DBI – The Danish Institute of Fire and Security Technology has just launched a new project called 'The Biogenic Industrialised Construction - Construction, Fire and Architecture', which aims to develop and fire test prefabricated structures in biogenic materials scaled for multi-storey industrialised construction. The project builds further on the collaboration and results from the previous MUDP project 'Thatched Facades for the Green Transition', which showed that it is possible to use clay as fire impregnation on thatched facades.

Exterior walls with straw

Whereas the first project focused on the outer layer of the exterior wall, the new project concentrates on the entire exterior wall construction – more specifically: exterior walls in straw/wood with thatched facade solutions and clay as a fire retardant. In addition to developing fire-safe constructions made of biogenic materials, it is also important in the project to secure the joints between elements, as they can also have an impact on how a fire develops or can be stopped.

"The straw elements will consist of a light wooden skeleton filled with hard-pressed straw. As we focus on materials and solutions that have the least possible impact throughout, we want to use straw that is processed as little as possible," says Anders Dragsted, engineer and head of DBI’s Advanced Fire Engineering (Buildings) department. He adds:

"We are not looking for signal value, such as when cladding concrete with wood. Instead, we want to avoid CO2-heavy materials as far as possible, which are often required to protect biogenic materials against fire. The vision of radically lower CO2 emissions applies to the entire value chain in connection with production, processing, transport, installation and use. At the same time, we are focusing on the potential for reuse and recycling of the materials - i.e. that they must be easy to disassemble and not be 'contaminated' with various chemicals," says Anders Dragsted.

Prefabricated constructions

Thus, part of the sustainable solutions in the project also consists of the biogenic model constructions being prefabricated and installed after they have been thatched.

"Normally, thatching is done outdoors directly on the building. Instead, the project will involve thatching modular elements, which will then be transported to the building site and installed. It is a way of creating industrialised processes and workflows and thereby making construction more efficient. It is the sum of materials and the way they are put together that makes up the efficiency improvement," says Anders Dragsted, adding:

"At the same time, the thatchers will use the project to develop their craft to match prefabrication.

DBI conducts fire tests

As with the first project, DBI is also responsible for all fire tests in the new project. And the new project will probably start where the old one ended.

"In the first project, a number of mini-SBI (Single Burning Item) tests were conducted to identify the method and kinds of fireproofing that had the greatest potential. It turned out to be moraine clay, on which we then carried out several downscaled facade tests. In the new project, we will probably start with scaled facade tests and possibly end with a full-scale facade test. However, what exactly will happen must be revealed during the course of the project," says Anders Dragsted.

Inspire and push the construction industry

Even though the project should show good results in line with the results of the first project, according to Anders Dragsted it is probably not realistic that the construction industry will immediately start building exterior wall structures consisting of straw and clay as fire retardants.

"Therefore, our ambition is rather to inspire the industry and push the boundaries of what is considered viable in construction. If we show that it is actually possible to build fire-safe and efficiently with biogenic exterior wall constructions like those in the project, there may be some who dare to continue working on the idea," says Anders Dragsted and explains:

"If, at the same time, we have taken the first step and saved the industry the initial money, we can hopefully influence some people to think 'new-old' and continue our work".

Read also: DBI project on covered facades wins awards in both Denmark and abroad