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Comparative study provides insight into lower environmental costs of biobased building materials
Wood, flax, elephant grass or biocomposites made from plant-based raw materials are attracting a lot of attention in the construction industry. And not without reason. These so-called biobased building materials can help in the fight against climate change. But what is their actual environmental impact? And how do they compare with conventional building materials such as concrete or 'fossil' plastics?
Wageningen University & Research (WUR) investigated this, using three reference houses, as part of the project Biobased building products in the Dutch Environmental Database. In this database, architects and property developers can find information for calculating the environmental performance of a building (MPG).
The MPG is increasingly being used as a granting criterion in construction projects: the lower the environmental impact, the more favourably the client evaluates a tender. This should make it easy to choose biobased building materials, provided they are in the database. This is often where the shoe pinches. Project leader Martien van den Oever (researcher at Wageningen Food & Biobased Research): “That was exactly what prompted this project: the relative invisibility of bio-based construction materials. Many of these materials are relatively new. They have often been developed by smaller companies and marketed in small quantities. They have been less concerned with making their environmental impact visible. That was a fundamental element in this project.”
One component of the project was the creation of a clear calculation methodology to map biogenic carbon storage, also known as 'CO2 sequestration' (see the box below). Another was to produce life cycle assessments (LCAs) of 13 biobased products not yet included in the NMD database. And the sub-study, which has now been completed and reported, compared the environmental impact of biobased and conventional versions of three reference houses: a terraced house, a semi-detached house and an apartment. It looked at biobased alternatives to conventional building materials, such as timber frame construction and cross-laminated timber (CLT) as an alternative to concrete and sand-lime brick.
Biogenic carbon in building materials
As a plant grows, it absorbs CO2 from the atmosphere. When the same plant is incorporated into a bio-based building product, this carbon storage helps to reduce current CO2 emissions. Sounds good, but it is a temporary solution, because one day the stored carbon will be released again. Nevertheless, biogenic carbon storage in building materials is attractive right now because it gives society extra time to work on sustainable solutions, up to 75 years or even longer. “We can use this time to develop methods to permanently reduce CO2 emissions or to find other solutions to climate change,” says Van den Oever. “After all, we are still a long way from net-zero CO2 emissions.”
For this research, WUR joined forces with several partners, engineering and architecture firm IA Bouwkunde, LCA expert Agrodome, Centrum Hout and the National Environmental Database (NMD Foundation).
Major differences
The main conclusion is that with biobased building materials, the environmental impact of a house is on average 18 to 33% lower than with conventional materials. Not only because of the direct environmental impact of the materials themselves, but also indirectly: “With biobased construction, for example, the foundation can be made lighter because the materials used are less heavy than concrete. This results in a significantly lower environmental impact,” Van den Oever explains.
The relative difference between biobased and conventional materials is even greater than might appear at first glance. This is because a number of activities and materials are the same for both types of materialisation. For example, 25-50% of the total MPG is determined by components like (electrical) installations and site layout, which are similar for both biobased and conventional construction projects. The lower the overall environmental impact, the higher the proportion of such 'standard' elements: it ranges from 23% for a semi-detached house based on concrete (high MPG) to 54% for an apartment building based on CLT (low MPG).
The impact categories that determine the MPG the most include global warming potential (potential impact on global warming), human toxicity and acidification. Together, these categories account for 85-88% of the total environmental impact. This applies to all building types and materialisations.
Conflicting regulations
Although research shows clear benefits of bio-based construction, these are not yet recognised in regulations. There are differences in how the environmental impact of building materials is dealt with at national and European level.
The basic methodology for calculating environmental costs includes 19 impact categories. Due to uncertainties in the calculation methods, the European Union has provisionally excluded six categories. The Netherlands, however, takes a different approach: it wants to include these six categories, while at the same time - like the EU - it does not recognise a crucial factor such as biogenic carbon storage (CO2 recently removed from the atmosphere) in the environmental impact calculations (see the box below).
Valuation formula
The storage of biogenic carbon in bio-based building materials is valuable, but is currently not included in the environmental assessment of buildings. Therefore, the Netherlands Environmental Database Foundation (NMD) asked WUR to propose a valuation formula that can be easily applied to all building materials, whether bio-based or fossil. The chosen time horizon is 100 years. This period is already used in LCA calculations to determine global warming potential (the impact on global warming). “This time period is long enough to avoid burdening future generations with our greenhouse gas emissions, while short enough to stimulate action,” says Van den Oever.
This leads to contradictory results. “It is extraordinary that the Netherlands includes certain less reliable impact categories, while ignoring an easily measurable factor such as carbon storage,” argues Van den Oever. A reliable method for determining environmental costs would not only provide clarity for the construction industry, but also contribute to a faster acceptance of biobased materials in the construction sector.
The project Biobased building products in the Dutch Environmental Database was co-funded by TKI Agri-Food under project code LWV 20.289.