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Decarbonising infrastructures – CO2 reduction potential in timber construction

Simplified life cycle assessments were conducted on six pairs of representative objects to estimate the potential for decarbonisation resulting from replacing concrete with wood in the construction phase.

Factsheet

Situation

Under the Paris Climate Agreement, Switzerland has committed to halving its greenhouse gas emissions by 2030, compared to 1990 levels. Furthermore, Switzerland’s Climate and Innovation Act has set the target of achieving climate neutrality by 2050. One of the fields of action for reducing greenhouse gas emissions is infrastructure construction. On 30 November 2021, the Swiss Parliament referred motion 21.3293 by Councillor of States Jakob Stark on research and innovation of wood as a material for use in infrastructure construction as a contribution to decarbonisation to the Federal Council. BFH was commissioned to investigate the possibilities for decarbonising infrastructures and, in particular, to estimate the decarbonisation potential resulting from replacing concrete with wood in the construction phase (subproject 3). On 6 December 2024, the Federal Council adopted the decarbonisation strategy for infrastructure construction with a focus on wood. It thus fulfilled motion 21.3293 by Jakob Stark, Councillor of States.

Course of action

The overall project comprises three subprojects that were conducted at BFH: a) Subproject 1 – Decision-making processes for materialisation, b) Subproject 2 – Technical expertise, c) Subproject 3 – Carbon reduction. potential and end-of-life scenarios for timber construction. In subproject 3, comparative life cycle assessments of concrete and timber designs were conducted on six representative infrastructures (wildlife overpass, noise barrier, cross-axis bridge, tunnel false ceiling, noise control gallery and cut-and-cover tunnel). The calculations were conducted in accordance with the KBOB rules, which are the reference for life cycle assessments in the construction sector in Switzerland, particularly for public procurement. Consideration was given to production, transportation to the construction site, disposal and material replacement during the exploitation phase. Greenhouse gas emissions, as well as primary energy and environmental impact scores, were determined for these phases. The hypotheses for the objects were made together with the Federal Roads Office (FEDRO) and the engineering company Timbatec Holzbauingenieure Schweiz AG. Furthermore, a sensitivity analysis was conducted for each design variant to illustrate the framework within which the results were achieved. Finally, recycling options for the wood components at the end of life and the carbon storage potential in wood and concrete were described and discussed. The report was verified by a third party, Empa.

Result

Using wood rather than concrete reduce greenhouse gas emissions by between 2 and 70%. However, there are significant differences between the objects under consideration. The most significant reduction in carbon emissions (70%) was achieved for the noise barriers, while the smallest reduction (2%) was recorded for the wildlife overpasses. The quantity of biogenic carbon stored in timber infrastructures is considerable. It can reach several times the carbon emissions emitted during the life cycle phases under consideration. Given the assumed lifetimes of infrastructures, carbon storage is considered to be long-term, though not permanent in the climate-relevant sense. The quantity of carbon stored by concrete carbonation over the lifespan of the infrastructures, in relation to the greenhouse gas emissions from the production, transport and disposal of all the materials used, is relatively low due to the large component thicknesses of the objects under consideration. The values for these objects are generally between 0,4 and 2,5%, and just under 13% for noise reduction barriers due to the more frequent replacement of the relatively thin sound-absorbing elements. On 6 December 2024, the Federal Council adopted the decarbonisation strategy for infrastructure construction with a focus on wood. It thus fulfilled motion 21.3293 by Jakob Stark, Councillor of States.

Looking ahead

With the aim of decarbonising infrastructures, the authors propose the following measures: 1) More detailed life cycle analyses, taking into account the phases of construction (A5), use (B) and, where applicable, effects outside the system boundaries (D) are necessary in order to validate the results of the study and derive effective measures for reducing emissions. 2) An almost emission-free construction method is not possible with today’s technologies, even in timber construction. In order to achieve the climate targets, concepts must be developed that significantly reduce greenhouse gas emissions in the manufacture of timber construction elements. In addition, further advancements are required in technologies that reduce carbon emissions in the production of cement clinker and concrete. 3) To avoid the development of moisture pockets and the need for chemical wood protection, constructive wood protection measures must be applied consistently. And when planning and implementing wood infrastructures, it is essential to ensure the separability of components. 4) A reduction pathway for permissible greenhouse gas emissions in infrastructure construction must be developed. 5) It would also seem reasonable to adopt an approach that allows timber buildings to be counted as temporary carbon reservoirs, combined with a legally binding obligation for subsequent permanent storage or for recalculation of the calculated storage capacity.

Contact

Prof. Dr. Aude Chabrelie

  • Dozentin
  • +41 31 848 63 43

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