Small-scale fire tests with broad perspectives for the construction industry’s climate footprint

Published: 18.08.23

DBI has successfully conducted 39 indicative small-scale fire tests on 14 different bio-based structures. This forms part of the ‘Fireproof Bio-Based Structures’ project.

Experts point out that the building industry’s climate footprint must be reduced to 2.5 kg CO2e/m2/year by 2030. This is why we need to build with bio-based materials that absorb CO2 during growth and are renewable.

But bio-based materials are combustible, and structures that remain within 2.5 kg CO2e in climate terms on paper can prove difficult to build in reality. The instructions in the building regulations often entail requirements for the use of non-combustible insulation, or that the bio-based insulation materials are protected by CO2-heavy materials.

“But fire doesn’t have to put a stop to bio-based structures. It just has to be borne in mind early in the design phase that the critically combustible materials are adequately protected,” says Asmus Haastrup, Research Consultant at DBI.

Fireproof Bio-Based Structures

Together with seven partners, DBI has just completed the Fireproof Bio-Based Structures project, in which 39 indicative small-scale fire tests of 14 different bio-based structural compositions have been conducted. An indicative test is a fire test that provides indications of how a structure will perform during a full-scale fire test.

Tests were conducted for 60 minutes on fire cell walls (EI 60), 10 minutes on bio-based cladding (K1 10) and 60 minutes on bio-based fire protection systems (K2 60). Of the 14 structures, only two fail to meet the test requirements in the indicative tests.

“The aim of the project is to show how to build with as close to 100% bio-based materials as possible and still end up with structures that can pass the fire test and thereby comply with the pre-accepted solutions in the building regulations. The project fits in with the current mindset in the construction industry at present, where bio-based and hygroscopic structures are in demand – i.e. where moisture through the structure itself can even out over time,” explains Asmus Haastrup, Project Manager for the project, adding:

“We have therefore worked with clay, lime and hemp concrete, for example, as substitutes for cladding materials such as plaster, and combined these materials with various bio-based panel materials and insulation types, including grass and straw.”

Three key challenges

But the project is much more than a research project. It aims to help reduce the risk for developers, architects, designers and craftsmen by building bio-based structures and helping to really kick-start bio-based construction in Denmark.

“Basically, we face three challenges in terms of accelerating the use of bio-based materials here in Denmark. The first is that in our pre-accepted solutions for fire, we have different requirements for the fire properties and documentation of materials and structures than those of other European countries’ building regulations. It’s often required, for example, that the fire-retardant cladding is K₁ 10, which means that it’s been tested on the specific substrate on which it is to be used. In other countries, you can get away with testing on a generic substrate and then being able to use all kinds of underlying materials – for example, if you have a K₂ 10 classification. In practical terms, this means that documentation from foreign suppliers is often not valid in Denmark,” says Asmus Haastrup, continuing:

“The other challenge is that today there is unbelievably little freedom of design in relation to bio-based materials and fire. This is linked to the fact that very few tests have been conducted – and those that have been are perceived as a competitive advantage by the manufacturers and are therefore rarely shared with the public. If we continue at our current pace, it will easily take 50 years before we have the same design options that we have right now with conventional materials.

“The third challenge is that even if we get to grips with the documentation, neither designers nor contractors in the construction industry are geared up to building with bio-based materials. Basically, it’s about creating a new way of building, taking the materials into account. Moisture is important, because we’re dealing with materials that are more exposed to rot and mildew, but fire is an equally important consideration – both when planning and out on site,” says Asmus Haastrup.

Education and partnerships

In the project, design students and the participating manufacturers have designed structures that meet requirements and regulations for properties other than fire, such as U-value and acoustics.

“As things stand right now, designers do not have the necessary knowledge of fire and peace of mind to choose bio-based materials. This project is crucial for us to push a new generation of designers into the construction industry who are properly equipped and prepared to plan bio-based projects,” says Jess Grotum Nielsen, Assistant Professor at VIA University College.

According to Asmus Haastrup, however, education is only half the answer if we are to see rapid changes in the construction industry. The other half is the need for money for documentation, and this is where he believes that partnerships are needed:

“It’s clear to me that it’s possible to both build bio-based and meet the applicable requirements for fire testing and the requirements of the pre-accepted solutions. I hope that many people will find inspiration in the tests we’ve conducted, and that they will take the next step. If we’re to have a rapid development of bio-based construction and greater freedom of design, classification fire tests must be conducted on a full scale – and lots of them! This is a financial burden that manufacturers cannot bear alone. And that’s why we’re encouraging a dialogue between actors in the construction industry,” says Asmus Haastrup.