# End-of-Life Scenarios for Mass Timber: Assumptions, Limitations and Potentials--A Literature Review
## 3 Results
### Inconsistencies in the EoL Scenarios of EPDs  
Environmental Product Declarations (EPDs) for mass timber are increasingly used to assess the environmental impacts of wood products in construction, with the aim of supporting better decision-making in selecting sustainable building materials for practitioners from the industry. Within the literature review, 18 studies mentioned EPD in their investigations, 12 have pointed out that the current state of EPDs includes a significant number of assumptions and limitations, making it difficult to achieve the goal of implementing material circularity in reality. The main inconsistencies and discrepancies stem from the biogenic CO2 values resulting from sequestration of carbon in mass timber, varying system boundaries across different EPDs, variations among generic and specific databases, and the end-of-life scenarios (C stage) in EPDs.  
Although carbon content and the EoL possibilities were seen as the major advantages of wood products [64], they introduce the biggest degree of uncertainties and variations in EPDs due to the density of wood used and EoL choices based on assumptions [65]. As mentioned in Section 3.2, the sequestered biogenic carbon content is closely linked to the chosen EoL scenario, as the negative biogenic CO2e value reflected in EPDs must be counterbalanced after the product reaches its EoL. In [PERSON]'s studies [65], several EPDs reported a negative total GWP after stage C, due to the EoL definitions applied for the products in the EPD. Eighteen out of 71 EPDs included only the production stage A1-A3, without consideration of the release stage C. The total GWP could be misleading as the omitted C stages could make the product seem like a more 'climate friendly material' but in fact it is the result of inconsistent reporting. Other negative total GWP values may also result from the EoL option of landfill, as landfill scenarios are sometimes assumed to provide permanent storage capacity for biogenic CO2e [65].  
According to [PERSON] et al. [66], generic life cycle inventory databases can yield significantly different carbon footprint values for the same product compared to industry EPDs. These discrepancies arise from variations in the fuels used by local manufacturers, production processes, and the selection of raw wood materials. [PERSON] et al. [67] also pointed out that generic data from broad LCA databases might not reflect the specific production processes or regional variations as they are mainly provided by academics and consultancy firms. They emphasized that mixing data for LCA calculations should be avoided. It is therefore critical to improve the requirements of generic LCA databases depending on the use in practice.  
In addition, [PERSON] et al. [68] and [PERSON] et al. [69] both noted that varying assessment methods can result in inconsistent allocations of environmental impact results, making comparisons between different wood-based products difficult. In addition, different verification processes of EPDs have been found among EPD operators and individual verifiers due to the discrepancies among Product Category Rules (PCRs) [69; 70]. Therefore the harmonization of methodologies, system boundaries and data verifications is critical in providing reliable and comparable EPDs for accurate and valid environmental impact assessment.