The feasibility of timber as a structural material for mid-rise residential buildings in the Netherlands

Abstract

The construction sector aims to reduce its environmental footprint to address climate change and material depletion, with an increasing focus on reducing embodied carbon. Simultaneously, there is a growing demand for affordable housing in the Netherlands. A significant part of the new housing stock needs to be mid-rise residential, efficient in both material and land use. Bio-based materials, such as timber, which are renewable and have relatively low carbon emissions, could play a key role in reducing embodied carbon for these types of buildings. Since structural systems often account for the majority of a building’s embodied carbon, using timber here can offer significant advantages. However, its application in practice remains relatively uncommon in the Netherlands.

Although existing research highlights the potential of timber in structural systems, challenges such as limited knowledge, lack of incentive and financial barriers are often cited as key reasons for its limited adoption. This research aims to address these challenges by exploring and quantifying to what extent a shift toward timber-based structural systems can reduce the environmental footprint of mid-rise residential buildings in the Netherlands, while maintaining economic feasibility. By doing so, this research aims to offer practical insights into the use of timber in construction, addressing knowledge gaps and identifying the conditions for its application in practice.

A comprehensive literature review was conducted on environmental regulations, assessment methods, structural systems, and suitable compositions of structural elements using timber. The insights gathered were applied to a case study, where various redesigns were developed and optimised under different boundary conditions. The environmental impact was quantified by a life cycle assessment using the Paris Proof Indicator (PPI, measured in GWP-GHG). Simultaneously, economic feasibility was quantified by an evaluation of construction costs. The scope of the assessments is limited to the life cycle stages from cradle to practical completion, emphasising the importance of direct impact.

As a result of the assessment of the case-study redesigns, several building concepts provided significant reductions in environmental footprint while being economically feasible. Compared to the original design, hybrid redesign concepts with calcium silicate brick walls and CLT-concrete composite floors can achieve PPI reductions up to 42% while being of equal or lower costs. Concepts with CLT walls and hollow core timber floors can even lead to reductions of PPI up to 55%. Within a 10% increase in costs, a wider range of concepts can lead to similar PPI reductions. All concepts with both CLT walls and CLT floors proved to be economically unfeasible within the stated cost thresholds.

The associated PPI values were found within the range of 82 and 114 kg CO2-eq./m², depending on the building concept. Accounting for design variations between mid-rise residential buildings, research uncertainties, and potential design optimisations, the building concepts researched could align with the Paris Agreement targets up to 2035. As the targets for 2050 are roughly twice as strict, it is unlikely that these are achievable within the researched design strategies. Incorporating reused or recycled materials and/or accounting for the benefits of temporary carbon storage in bio-based materials will likely be necessary to achieve these targets.