Aarhus University Seal

Agricultural side-stream biomass can store CO2 in buildings

Biogenic building materials consisting of grass, sugar cane and eelgrass can reduce the construction industry's climate footprint, and they also have a large CO2 storage potential. New synthesis shows results from interdisciplinary project work that brings climate-heavy industries together to develop circular productions.

Prototypes of biogenic building materials from the project's exhibition house for the Building Green conference in April. Sheet materials of rapeseed (left) and clover grass (right). Photo: Torsten Sack-Nielsen, VIA University College.

The Danish government has adopted a law on climate neutrality in 2045, and therefore it is being discussed at political level and across sectors how Denmark can fix and store more CO2 than the country emits.

About 60 pct. of Denmark's CO2 emissions come collectively from construction, food production and agriculture, and in the project ‘Fra marken til byggeri’ (‘From field to construction’), supported by Realdania and the Rambøll Foundation, these three industries have come together to find solutions to be able to reduce their climate footprint by using side-stream biomass from agriculture as building materials.

The production of building materials is currently very damaging to the climate, but based on using existing biomass, side streams from agriculture, the project attempted to describe more climate-friendly manufacturing methods. In addition, the biomass fixes CO2, and thereby the buildings can act as carbon stores for several years.

This is the basic idea of circular bioeconomy: to use existing and local biomass as a resource in the production of materials that are necessary for people, and to exploit the biomass's full potential with a minimal climate footprint.

The project will be a living laboratory

An interdisciplinary group consisting of architects, craftsmen, and researchers – including professor Uffe Jørgensen and research assistant Emil Dahl Nielsen from the Department of Agroecology – has been working on the project since 2022.

The project consists of three tracks: in track one, 12 crops that can be grown in Denmark were analyzed and quality assessed in relation to e.g. biodiversity and nitrate leaching. In track two, prototypes of biogenic insulation and board materials were produced, where their qualities are still being assessed in relation to current building materials. Based on those results, track three will consist of the construction of a Living Lab in the form of a new restaurant run by Moment's owners located in Tvingstrup between Aarhus and Horsens, which will consist of - and test - biogenic building materials.

In January, a knowledge synthesis was published with the preliminary results from the project and analyzes are still being carried out in track two, and the plan is for the construction of the test center to begin this year.

Crops can be several valuable products

Denmark does not have so much forest growth that enough local wood can be produced for building materials, but there are large agricultural areas for food production, where the carbon-containing side streams can be used for building materials instead of being burned or biologically degraded, and CO2 is released to the atmosphere.

"You can't say that we should only grow building materials instead of food in Denmark, that would create a need to grow food elsewhere, so instead I would argue for using side streams from primary production or trying to make primary production bigger. Colleagues and myself have argued for many years that if we grow grass instead of grain, we can increase the overall productivity per acres. If it is used for food, feed and building material, then you can still deliver the same amount as today," says Uffe Jørgensen.

He and Emil Dahl Nielsen have assessed agricultural crops and potentially new crops in relation to nine planetary boundaries – that is interfaces for how much we humans can influence the earth without causing environmental imbalance; and with this starting point, they have selected 12 annual, perennial, and marine crops that stand out as suitable biogenic biomass for construction.

"The construction industry is interested in planetary boundaries because, as an industry, they are regulated in relation to how much CO2 must be used per square meter of construction, as it is a very resource-intensive industry," says Uffe Jørgensen.

The suitable crops include annual sugar beet, which has a very high biomass production primarily for refining sugar, and the by-product is a carbon-containing fiber pulp. Clover is a perennial crop that can fix CO2 over a long growing season with multiple harvests, and several products such as feed and food protein can be refined to replace the CO2-heavy soy imports. Marine crops include washed-up eelgrass, which does not take up agricultural land, and its high salt content minimizes the risk of fire and decay.

"There is still much that needs to be clarified in relation to the building technical properties of the biomass; especially grass fiber, such as their properties for sound insulation, moisture transport, fungal growth, allergies and as a fire-retardant material," says Uffe Jørgensen, who, together with Emil Dahl Nielsen, will create analyzes and scenarios for how much Danish biomass the construction industry can use in the future, as well as make calculations for how much CO2 storage the biomasses have.

Cheaper storage in buildings than in the underground

Agriculture fractionates large amounts of biomass, and it therefore has a large storage potential if it can be used in construction.

"The reasoning behind biogenic construction is that biomass materials can take CO2 from the atmosphere and store it in buildings; then it can function as what we call "negative emissions". The same will be tried to be achieved by capturing CO2 and pumping it in the underground. Therefore, the government has set aside approximately DKK 28 billion for the next phase of CCS, 'Carbon Capture Storage', but I think it can be made cheaper and more understandable for us citizens by storing it in buildings. It is not certain that we can store enough, but what we can, should be stored there," states Uffe Jørgensen and continues:

"It is an important agenda that the construction sector can probably store CO2 more cheaply than in the underground. But unfortunately, the focus for the time being is only on storage in the underground."

But there are a couple of rules in the building regulations that put the brakes on the development of the biogenic building materials.

"One of the major discussions we have had in the project group concerns a few rules in the EPD, 'Environmental Product Declaration', which is the calculation of a building's climate impact. One of the rules is that biogenic materials must be calculated as burned when the building is removed, which means that CO2 is released into the atmosphere, and the other rule is that a building lasts for 50 years. We do not understand the two rules, as the vast majority of buildings last for many more years. The rules prevent the spread of biogenic building materials, because the calculation of regenerated CO2 gives the biogenic materials relatively high EPD values," says Uffe Jørgensen and states:

"We don't yet know how long we can store CO2, but it is unthinkable that in 50 years we will simply tear down buildings and burn them; instead, the CO2 will probably be captured and recycled and thus not released into the atmosphere. We are just learning to act sustainably by recycling as much as possible, so it would be unwise not to do that.”

About the project

‘Fra marken til byggeri’ (‘From field to construction’) is supported by the Rambøll Foundation and Realdania, and it is led by VIA University College in Horsens.

Professor Uffe Jørgensen and research assistant Emil Dahl Nielsen from Department of Agroecology and Center for Circular Bioeconomy (CBIO) are included as project partners together with VIA University College, Restaurant Moment, Henning Larsen Architects, Borg Rådgivning and TræVærk.

The project period was from 2022-2023, but the work is continued this year with tests and the establishment of a Living Lab: a restaurant for Moment in Tvingstrup, which will consist of - and test - biogenic building materials.

Read about the project and its knowledge synthesis 'Pathways to biogenic construction' here: From the field to construction (realdania.dk) 


Professor Uffe Jørgensen

Department of Agroecology