Building a sustainable future: a comparative life cycle assessment of a cross-laminated timber and a lightweight steel frame building

Abstract

The Netherlands has faced rapidly increasing housing prices over the previous years. As a counter measure, the government is aiming to increase the construction of new houses from around 70 thousand annually to 100 thousand annually, to achieve 900 thousand new houses by 2030. At the same time the world is facing a climate crisis and the Netherlands has pledged to decrease its emissions by at least 50% in 2030 in respect to 1990. The country must therefore reduce the impact of new built houses to be able to build more while reducing the total emissions.
Currently most houses are built with reinforced concrete which is generally not seen as a sustainable construction method due to the carbon emissions related to cement production. Building houses with cross-laminated timber panels or lightweight steel frames are proposed alternatives with a lower expected carbon footprint. This study was set up to perform a life cycle assessment of a steel and a timber building to compare their impact and find out under which circumstances building with steel or timber is a more sustainable option. A case study was found of a timber building and a hypothetical alternative was designed with steel frames which were both studied under three scenarios. The scenarios represent the choices that could be made regarding material production and waste treatment, ordered from worst-case, to expected, to best-case scenario.
When including the climate impact of construction, the treatment of waste, end-of-life benefits and carbon storage, the timber building performed better than the steel building in every scenario regarding global warming. However, waste treatment, end-of-life benefits and carbon storage are all dependent on future processes and emissions happening after 2030. When only the construction is included, the steel building outperformed the timber variant in the expected and best-case scenario. For this reason, building more houses with lightweight steelframes produced with at least 50% recycled steel would be the most beneficial for the Netherlands to reach its 2030 climate goals. When taking a longer timespan into consideration, timber buildings are the preferred choice due to the carbon storage effect, as long as the forests are replanted sustainably.
Either alternative was found to be a better alternative than the current houses built with reinforced concrete. If all houses built before 2030 were made with the alternative production methods this could save at least 20 Megaton of CO2 emissions. Because the alternatives researched made efficient use of materials, no significant issues were found for the demand of wood or steel in the Netherlands. In fact, steel demand is likely to decrease due to the reduced need for reinforcement steel. Further improvement on both alternatives is possible by increasing the potential lifespan of the buildings and reducing the emissions related to energy use in the production of materials.
The outcomes of this study may influence decision making depending on the weight the Dutch government gives to its climate goals of 2030 versus its total impact on climate change. Constructing steelframe houses may reduce construction emissions by 4% compared to timber by 2030 but would result in 64% more emission in 2100 due to the missed-out carbon storage. In general, the construction industry can improve a lot by increased use of low-carbon alternatives such as lightweight recycled steel and biobased materials.