# Space Efficiency in European High-Rise Timber Buildings
## 2 Methods  
The utilization of the case study technique was employed for the purpose of classifying and consolidating information concerning 56 modern high-rise timber projects in the European context (Figure 1). This approach is often used in academic research to structure and unite information about current timber-based office projects. It integrates both qualitative and quantitative data, in addition to a comprehensive review of the existingliterature [57,58], allowing for a systematic investigation of their architectural and structural aspects. This method facilitates a comprehensive assessment of particular instances in practical environments, fostering a deep comprehension of the distinct attributes and trends in contemporary office designs that utilize timber as a primary material. The selection of 56 cases in this study ensures robust and representative results, particularly given the inherent scarcity of accessible contemporary European high-rise timber buildings. This sample size allows for the identification of significant trends and patterns in spatial utilization and architectural features. The diversity among the selected cases, spanning various geographical locations in Europe, building heights, and design typologies, enhances the generalizability of the findings. Notably, the study examines timber towers across Europe from a wide array of countries including eleven in Norway and Sweden, nine in France, seven in the United Kingdom, five in Finland, four in Germany, three in the Netherlands, two in Switzerland, and one in Denmark, Austria, Italy, and Spain (as depicted in Figure 2 and detailed in Appendices A and B). By encompassing such diversity, the research offers a comprehensive view of current practices in high-rise timber construction. Methodologically, a sample size of approximately 30 cases is adequate for deriving meaningful conclusions in the existing literature, balancing depth and breadth of analysis as evidenced by prior research [23,39,42]. Thus, the examination of 56 cases forms a robust foundation for understanding spatial utilization in European high-rise timber buildings, ensuring the study's insights are both reliable and widely applicable, facilitating the identification of recurring themes such as function, core typology, form, structural system, and different construction materials. In an extensive undertaking, this paper thoroughly assessed the floor plans of a variety of timber edifices, including typical stories. This thorough method promised the gathering of accurate and dependable information, establishing a robust foundation for assessing spatial effectiveness in the sample cases. In general, when classifying high-rise structures according to their anticipated use, they are divided into those designed for a single function or for multiple functions. This article bases its evaluation of utility on the following categories: residential, office, hotel, and mixed-use. Moreover, following the established academic literature [59, 60, 61], we utilized the thorough classification system [36,37] for the key components in architectural and structural planning. This choice was motivated by the specific features of these classes, as illustrated in Figure 3.  
Figure 1: Research method (created by the authors). Figure 3: _Cont._  
Figure 2: High-rise timber buildings located throughout Europe (created by the authors). In this study's methodology, space efficiency was evaluated by determining the ratio of NFA to GFA, thereby providing a quantitative metric for the effective utilization of the available space. The service core to GFA ratio was calculated, offering insights into the allocation of space dedicated to the main structural and service components within the building. Assessment of space efficiency includes two critical ratios: NFA to GFA and service core to GFA. The NFA is derived by subtracting the service core area from the GFA, isolating functional areas where activities occur and excluding spaces allocated to infrastructure and supplementary facilities.