Purpose: The production of new building materials is behind 11% of the global CO2
emission, pressuring the construction sector to seek new alternative materials to assist the
sector to reduce its Global Warming Potential (GWP). Bio-based material absorbs CO2
during their lifetime which reduces CO2 emission to the atmosphere. Wood is the most
common bio-based element used nowadays, however, new materials are getting attention
from the construction sector, for instance, seaweed. To assist the Danish construction
sector to reduce its environmental impact a comparison between a load-bearing structure
using wood and seaweed will be made against the conventional concrete load-bearing
structure.

Methods: To assess the environmental impact of both load-bearing structures a Life Cycle
Assessment (LCA) is conducted for 1m² of load-bearing structure made of wood and
seaweed(WSW), and made of concrete and rock wool(CRW). A dynamic LCA (DLCA)
approach was chosen to analyse the impact of biogenic carbon since the WSW has biobased
elements in the composition.

Results and discussion: The LCA analysis showed the WSW element emitting 27,78% less
GWP when compare to CRW, however, it also presented an increase of 66,67% of land
use impact. Significant changes in the results were presented in different LCA approaches,
showing that the results are extremely sensitive to the chosen approach. This variation in
the results can mislead the benefits of bio-based materials.

Conclusion: For the Indirect Land Use Change(iLUC) approach, WSW showed less impact
in 6 out of 7 mid-point categories analysed, only showing a higher impact in land use
categories, showing that the use of more wood in the construction sector will require more
land to produce more wood. On the other hand, seaweed showed a lower impact in most of
the categories, however, the uncertainties about its end-of-life (EoL) demonstrated a higher
impact on marine eutrophication when having protein-rich fish feed as a by-product.