Biogenic materials – things we can harvest in the fields, the forests and at sea – should play a much larger role in the production of building materials, says senior researcher Torben Valdbjørn Rasmussen from BUILD, Department of the Built Environment at Aalborg University. Along with his colleagues he conducts research into how the building sector in Denmark can become more sustainable and contribute to the green transition.

One of the areas that presents the largest potential is by switching to biogenic materials as substitutions for stones, gravel, concrete, and steel in all the parts of construction where biogenic materials can fulfill the same functions.

- For instance, ground up mussel shells can replace sand, gravel, and light clinker in the capillary breaking layers to mitigate rising moisture. This means that it makes perfect sense to use them as screed and capillary breaking layers below the insulation at terrain deck level to prevent moisture from rising into the construction. They do this as well as mineral materials, that are obviously a limited resource, he says.

Buildings as CO2-depots

In relation to the green transition, the building sector in Denmark thus presents a very large, untapped resource. We have a tendency to use concrete and other mineral products in constructions where wood or other organic materials would have been just as useful, says Torben Valdbjørn Rasmussen.

- Concrete is useful in foundations, in the lower floors of tall buildings and in constructions that have to carry a lot of weight. There are many places where concrete makes perfectly good sense, but we could easily be using much more organic material in our buildings. Even the wooden houses that we build in Denmark could use more wood in the construction than they do today, he says.

In this way, we would be doing the environment and the green transition a great favour. Because wood and other organic materials harvest CO2 from the atmosphere, releases the oxygen and uses the carbon to grow, they act as a type of CO2-storage facilities. The more organic materials we can use in our buildings, the more CO2 we can prevent from being released back out into nature – for as long as the buildings stand. In Denmark alone, we would potentially be able to store up towards 100 million tons of CO2 in buildings over the next 50-75 years if we improved our ability to use biogenic building materials.

Climate accounts stall the green development

Nonetheless, Torben Valdbjørn Rasmussen remains hesitant when it comes to promoting the use of more wood in the Danish building sector at the moment. Unless the wood is grown and produced domestically that is. If it is, it can be counted in the Danish national climate account. Imported wood cannot – this means that the political incentive to support the green transition at this point is significantly lowered.

- We have arrived at a situation where it makes more political sense to spend resources on getting Aalborg Portland to emit less CO2 as it produces cement for the rest of the world than it does to support the Danish building sector in using more wood. Aalborg Portland’s CO2-emissions count in our national climate account, but the discount from non-domestic wood products do not, he explains.