Sustainable timber structures

Abstract

To meet the climate goals set by the government, the building sector needs to reduce its contribution to the environmental burden on society. However, the current situation in the Netherlands presents a major challenge to build more to reduce the housing shortage, while at the same time reducing its environmental footprint. Therefore, alternative solutions to the status quo should be considered, which can reduce the environmental impact of buildings. The goal of this thesis is to determine the environmental impact of multi-storey timber residential buildings and to make a comparison with a concrete building. Furthermore, the effect of cascading strategies on the environmental impact is analysed and the carbon sequestration potential by timber residential buildings estimated. Firstly, reference projects are studied to determine the trends in the timber construction sector. Based on these results, the main timber typologies and available design choices are mapped as well as the available (engineered) timber products available on the market. Secondly, the sustainability of timber structures is assessed by performing a literature study on three different scales: the macro-, meso- and micro-scale. The macro-scale represents the global forestry level in which the carbon cycle, carbon sequestration (i.e. capture and storage) and forest certification are discussed; the meso-scale represents the building level in which the durability and cascading strategies (i.e. strategies to elongate the lifespan) are discussed; the micro-scale represent the environmental impact of the material itself. Thirdly, the environmental impact is quantified using the fast-track life cycle assessment methodology. Two data sources are evaluated by performing a data analysis. The first being the ‘Nationale Milieu Database’ which is prescribed by the Dutch ‘Milieuprestatie Gebouw’, the second being Environmental Product Declarations according to the European EN15804 standard. For the two main timber typologies (mass timber and post&beam) a variant study is set-up using a parametric environment. The variant study analyses the environmental impact of main load bearing structures, the relative contribution of structural components and the effect of cascading strategies. The research is concluded by a case study in which the environmental impact of a timber alternative is compared with an equivalent concrete benchmark. Based on these results the global warming reduction potential of timber residential buildings is determined. From this research, it was shown that the environmental impact of timber buildings is lower than a concrete equivalent. However, it was found that the production capacity of engineered timber proved to be currently insufficient to reach the market potential, resulting in upscaling challenges for the engineered timber manufacturers when the demand will increase. From the data analysis, it was found that the selection of timber environmental data sources is highly sensitive. Furthermore, it was found that the choice for structural typology does not lead to significant differences for a default design lifespan. Though, the choice for a certain floor system does result in large differences. Overall, it can be concluded that a difference can be made to the environmental impact of the built environment by cascading scenarios, regardless of the choice of construction material. In case of timber structures, additional benefits occur due to the lower relative environmental impact and carbon sequestration.