# End-of-Life Scenarios for Mass Timber: Assumptions, Limitations and Potentials--A Literature Review
## 3 Results
### Current Assumptions and Limitations on LCA for Mass Timber  
Out of the 56 papers reviewed, the majority--45 papers--referenced the Life Cycle Assessment framework, since mass timber's EoL is an integral part of the LCA process. When discussing the EoL stage C and the benefits beyond the life cycle D it is important to understand the system boundaries these entail. Typically, LCA studies consider three primary approaches related to the analysed system boundaries: cradle-to-gate (stages A1-A3), cradle-to-grave (stages A1-C4), and cradle-to-cradle (which includes all stages with the addition of stage D) [3; 26]. However, these differences in system boundaries can lead to varied results and interpretations, making it particularly challenging to compare studies, especially when assessing mass timber. The discrepancies within the current LCA framework for mass timber were acknowledged by all 31 papers from the primary literature search result on the EoL of mass timber. It is argued that the EoL stage plays a crucial role in accurately accounting wood products' carbon pool size over time [27]. However, uncertainties in system boundaries, time horizons, and scenario assumptions in the LCA framework have led to the lack of compatibility  
Figure 3: Number of Articles Found on Scopus searching terms related to “Mass Timber” (**left**) and “End of Life of Mass Timber” (**right**). and even distorted climate impact assessments [28; 29]. For example, [PERSON] et al. [30] have highlighted the importance of time when considering the LCA of wood, as the \"idea of time\" could be highly scale-dependent when considering the growth of trees. In addition, being able to compare LCA results with mass timber projects across international boundaries is another unresolved gap among the international LCA community, due to varying local regulations, methods and measurements [18]. It is important to adopt a consistent, circular and time-comparable system boundary for long-lasting wood products like mass timber in order to ensure that global studies are relatable. A full circular system spans from raw material extraction to disposal and also considers the potential for materials to be repurposed at the end of their useful life. However, other scholars argued that while including stages beyond the production one (A1-A3) provides a more comprehensive view of the life cycle, it also introduces greater uncertainty due to assumptions about future events beyond stage A [31]. Consequently, it is urgently needed to have accurate and standardised characterisation of the service-life and end-of-life stages of mass timber. An additional key issue of the discipline is the timing of emissions. One of the approaches towards LCA, the \"dynamic approach\" has been developed to evaluate the impact of emissions at each time step. Initially introduced by [PERSON] et al. [32], this method considers the timing of emissions in LCA by utilising a dynamic inventory, which tracks emissions over time, along with dynamic characterisation factors. While static LCA assumes that all emissions occur simultaneously throughout a product's life cycle, dynamic LCA evaluates environmental impacts over different time spans, considering both the timing of emissions and the kinetics of their effects within the cosphere [33; 34]. Additionally, to better capture the impact of time, it incorporates time-dependent characterisation factors, such as forest rotation periods and tree typologies, which are often overlooked in static models [35]. As a result, this approach considers different growth rates: faster-growing species, in fact, absorb carbon more quickly than slower-growing ones. Longer rotation periods result in CO\({}_{2}\) remaining in the atmosphere for extended durations, thereby contributing to a higher Global Warming Potential (GWP) score. [PERSON] et al. [29] also utilised dynamic LCA to examine the influence of system boundaries and baseline factors in the LCA of products made from forest biomass.