Environmental Impact of Mass Timber
The environmental impact of materials, products, and buildings is crucially assessed through their entire life cycle. In the construction industry, this assessment considers various phases, including resource extraction, production, construction, use, demolition, and disposal. In this text, we will focus on the environmental impact of mass timber, examining their effects from raw materials to disposal, with a particular emphasis on carbon sequestration and sustainability metrics.
Mass Timber Research
Research has demonstrated that wood has an impressive ability to sequester carbon dioxide (CO2), with one cubic meter of wood sequestering approximately one tonne of CO2. In fact, the amount of CO2 absorbed by wood during its life cycle exceeds the emissions generated during the manufacturing process, making it an exceptionally sustainable option. Additionally, the use of prefabricated mass timber elements reduces embodied CO2 during construction and operation due to reduced transportation requirements. Prefabrication has been shown to decrease CO2 emissions by approximately 20 percent. Furthermore, the utilization of bio-based glues in mass timber products contributes to their non-harmful nature. Mass timber elements also require significantly less water compared to the production of an equivalent volume of concrete, with a water savings ratio of 30:1.
Wood is a renewable resource used worldwide; however, uncontrolled tree cutting practices can cause more harm than benefits. To mitigate this issue, international regulations, such as those established by the Forest Stewardship Council (FSC), are crucial in ensuring responsible sourcing. The FSC ensures that the amount of harvested wood is replenished to maintain the capacity for CO2 sequestration. Controlled forests often replace each cut tree with two to three new saplings, as younger trees are known to sequester CO2 more efficiently than mature ones. While the decay of branches from mature trees releases a certain amount of CO2, the densification of woods may also increase the risk of uncontrolled forest fires, which must be avoided at all costs.
Mass-timber structures, composed of standardized elements like CLT panels, glulam, and LVL, have a reduced environmental impact compared to other materials in various ways:
- Air pollution is minimized due to reduced transportation needs resulting from standardized element sizes, requiring fewer vehicles compared to concrete-based construction.
- Construction waste is almost nonexistent since mass-timber elements don’t require additional finishing or cutting during construction. In the demolition phase, these elements can be simply demounted from their connectors.
Mass-timber buildings have a positive impact during the use phase. Unlike concrete buildings, they sequester large amounts of CO2 and do not release it over time. Additionally, mass-timber buildings exhibit approximately 30 percent lower energy requirements compared to their concrete counterparts, thanks to their superior thermal performance. Furthermore, mass-timber elements, such as CLT panels, offer better fire resistance than concrete or steel structures.
When wood is reused in mass timber elements, the sequestered CO2 remains locked within the structure. However, if wood is incinerated after demolition, the sequestered CO2 is released. Therefore, the preferred approach is to design mass-timber products for reuse at the end of a building’s life cycle. Standardization of the manufacturing process enables each mass timber element to be easily integrated into new structures. Once its structural and load-bearing performance diminishes, the element can still find use as façade covering or other non-structural purposes. Currently, approximately 36 percent of used wood is recycled, while approximately 50 percent ends up in disposal sites. To achieve a transition towards a circular economy, these percentages will need to be significantly improved, reducing waste and pollution while halting global temperature rise.