Spatial Effectiveness in High-Rise Timber Towers: A Global Perspective

Abstract

High-rise timber structures signify a rising trend, thanks to their significant environmental and economic advantages that occur over their complete lifespan. Enhancing spatial effectiveness in these structures is a critical design consideration for project feasibility. Currently, there has been no comprehensive study on the space efficiency of such towers. This article analyzed 79 cases all over the world to deepen the knowledge of design features shaping spatial efficiency. The critical findings are as follows: (1) the most common architectural preferences include residential function, a centrally located service core, and prismatic arrangements; (2) the preferred structural material is composite, while a shear walled frame system is the favored structural system; (3) the average spatial efficiency and percentage of core area to GFA were recorded at 84% and 10%, ranging from the lowest values of 70% and 4% to the highest values of 95% and 21%, respectively; and (4) no significant differences were detected in the effect of core design approaches on spatial effectiveness if appropriately planned, with similar inferences drawn concerning form and the structural material used. This article will assist in developing design directions for different interested parties, including architectural designers taking part in the advancement of high-rise timber towers.

1. Introduction

Space efficiency in high-rise wooden buildings is a complex area of research and development, intersecting architecture, economics, technology, and sustainability [1]. As global urbanization accelerates, the need for novel and sustainable solutions in construction industry grows more urgent [2,3,4]. High-rise timber buildings, using advanced timber construction techniques, present a promising alternative to traditional steel and concrete structures [5,6,7]. This introduction examines key aspects in this emerging field, including architectural, economic, technological, sustainability, social, regulatory, and cultural perspectives.

Designing high-rise wooden buildings requires a deep understanding of timber’s properties and urban dynamics, leveraging its strength, flexibility, and aesthetic appeal to create robust, space-efficient structures [8,9,10,11,12,13,14]. While wood’s strength-to-weight ratio and engineered enhancements support complex buildings, challenges like stability, wind, seismic resistance, and durability must be addressed [15,16,17,18]. Hybrid systems combining wood with steel and concrete improve efficiency and safety [19,20,21]. Economically, initial costs may be higher, but savings can be achieved through reduced construction times and lower foundation costs, with rising demand for sustainable solutions potentially boosting financial viability [22,23,24,25,26,27]. Technological advances, including digital tools and prefabrication, optimize space efficiency, while ongoing research enhances timber’s fire resistance, acoustic insulation, and load-bearing capacity [28,29,30,31,32,33]. Sustainability is a key advantage, as timber has a lower carbon footprint and supports biodiversity, with wooden buildings being adaptable and easier to recycle [34,35,36]. Socially, timber buildings offer a warmer, more natural environment, improving occupant well-being and supporting local economies by creating jobs in sustainable forestry and manufacturing [37,38,39]. Effective implementation depends on evolving regulatory frameworks that adapt building codes to timber’s unique characteristics, with countries like Canada and Sweden leading the way [40]. Shifting cultural perceptions of wood as a viable material for high-rise buildings through education and successful examples is essential to increasing acceptance [41,42,43].

Despite extensive analyses of the technical, ecological, and financial aspects of wooden construction [44,45,46,47], there is a significant gap in research focused on spatial efficiency in wood constructions. Such research would enrich existing knowledge and provide valuable insights for stakeholders aiming to develop more effective and sustainable timber buildings.

In the field of spatial efficiency research in buildings, various studies have explored efficiency across different building types and contexts, highlighting both similarities and differences. Ilgın and Aslantamer [48], Aslantamer and Ilgın [49], and Tuure and Ilgın [50] focused on wooden structures, with efficiencies ranging from 78% to 88% in residential, office, and mid-rise timber buildings. Conversely, Ilgın [51,52,53,54,55], Ilgın and Aslantamer [56], and Aslantamer and Ilgın [57] examined skyscrapers of various uses and regions, finding efficiency ratios from 67% to 76%. Further, Ilgın and Aslantamer [58] and Ilgın [59] reported a 72% efficiency in prismatic and tapered towers, while Okbaz and Sev [60] identified conical architectural configurations as the most efficient in high-rise office buildings. In residential structures, Ibrahimy et al. [61] noted deviations due to poor planning in Kabul, while Hamid et al. [62] found that corner positioning enhances efficiency in Sudanese homes. Hotels also benefited from spatial efficiency, as studied by Suga [63]. In advanced technological contexts, Goessler and Kaluarachchi [64] showed significant efficiency improvements in high-density urban areas. On the other hand, Arslan Kılınç [65] highlighted that service core space increases with tower height. Sev and Özgen [66] focused on load-bearing and core configurations. Kim and Elnimeiri [67] emphasized optimal structural systems in multi-use buildings. Höjer and Mjörnell [68] proposed a model considering digitalization’s impact on internal use of the buildings, while Nam and Shim [69] found corner cuts minimally impacted efficiency in tall towers. Zhang et al. [70] improved solar gains in freeform designs with minimal efficiency loss. Saari et al. [71] linked higher spatial efficiency to achieving comfort goals in tall office structures, and Von Both [72] enhanced urban planning effectiveness through stakeholder assessments.

This literature review indicates a notable gap in works on spatial efficiency in high-rise wooden buildings worldwide. To address the gap, this paper analyzes 79 cases, examining critical architectural and structural parameters to identify key factors affecting space efficiency. It considers functional use, form, core planning, load-bearing systems, and materials. This study aims to provide design guidance for architects and stakeholders in high-rise timber tower projects, focusing exclusively on spatial use, intentionally excluding considerations of sustainable planning, such as energy efficiency, ecological impact, and disaster resilience, due to a lack of comprehensive data on the towers studied.

2. Methods

A case study approach was applied to gather, categorize, and scrutinize data from 79 modern high-rise timber projects around the world (Figure 1). This extensively used research technique enables detailed documentation of both qualitative and quantitative data [73,74,75]. By facilitating an in-depth exploration of architectural and structural attributes of these buildings, this approach permits researchers to thoroughly investigate real-world instances, supplying a solid framework for comprehensive inquiry. This technique provides valuable insights into the distinct design features and structural components, thus improving the comprehension of contemporary architectural implementations. By focusing on particular samples, researchers can identify similarities and variations across global designs, revealing emerging trends in modern architecture [76].

The definition of a ‘tall’ or ‘high-rise’ building is ambiguous, as no universal standard exists for the height or number of stories. The categorization of these terms, especially for wooden projects, remains contentious. According to the Council on Tall Buildings and Urban Habitat (CTBUH), a ‘high-rise timber building’ is defined as having eight or more floors [77]. This study used this definition. It is noteworthy that the CTBUH is a prominent public organization dedicated to promoting universal urban growth dialogue. This organization underscores the development of sustainable urban areas in the face of swift urbanization and the climate crisis. As an authority in this domain, the CTBUH decides the heights of tall structures and bestows prominent titles like “The World’s Tallest Building”. Through programs such as “Buildings of Distinction”, it recognizes outstanding projects that demonstrate exceptional design and novelty.

The inclusion of 79 towers in this article ensures a representative analysis, especially given the relative scarcity of modern high-rise wooden structures. This sample size enables the detection of key trends in spatial utilization and architectural characteristics. The variety of selected examples, encompassing different global locations, heights, and design styles, strengthens the generalizability of the results. This research scrutinizes high-rise wooden cases across a broad range of regions, including Canada, the United States, Sweden, Finland, Norway, Denmark, the Netherlands, the UK, Germany, Austria, France, Switzerland, Italy, Japan, and Australia (please see Figure 2 and Appendix A).

Critical data required for evaluating space efficiency were acquired from official online platforms of relevant project shareholders, encompassing architects, engineers, and contractors. The researchers are engaged in a meticulous process to locate and select floor layouts, encompassing re-drawing those of low-rise and typical stories, to produce more uniform and accurate numbers for examining the spatial efficiency of 79 examples. Additionally, this detailed method of applying comparable floor plans whenever feasible seeks to yield more reliable data on spatial efficiency. Conversely, structures with inadequate information about their structural systems and architectural plans were excluded.

Architectural and structural aspects influencing space efficiency encompass the following (please see Appendix B): (a) designated function of the tower encompasses residential, office, hotel, and mixed-use configurations, integrating various combinations thereof; (b) core planning; (c) form; (d) structural system; and (e) structural material.

Regarding core types, this paper, building on the earlier literature [78,79,80], employs categorization detailed in Figure 3, which offers a more exhaustive and comprehensive approach [49]. Notable cases of skyscrapers around the globe that utilize various core configurations include Burj Khalifa (central) [81], 53 West 53 (peripheral) [82], and ADNOC Headquarters (external) [83].

Concerning the categorization of architectural forms, as opposed to prior studies [84,85], the method by [49] is considered more thorough for classifying tall edifices, encompassing those with free configurations. A typical tall building can be divided into three sections: apex, main tower, and base. This research principally groups forms based on main tower formation, as illustrated in Figure 4. Notable cases of skyscrapers around the globe employing various forms comprise the following: Burj Khalifa (setback) [81], 53 West 53 (tapered) [82], and ADNOC Headquarters (prismatic) [83].

For the lateral bracing of high-rise towers, various structural system classifications are utilized in real-life applications and widely debated in the literature [86,87,88,89,90,91,92,93]. However, the terminology for structural systems can differ across sources, even when describing the same system. This article adopts structural system categorizations by [94] due to its more detailed and comprehensive characteristics, as shown in Figure 5. Notable cases of skyscrapers around the globe using diverse structural systems are Burj Khalifa (buttressed core) [81], 53 West 53 (framed-tube) [82], and ADNOC Headquarters (shear-walled frame) [83].

Structural materials are sorted in two key categories, namely, ‘timber’ or ‘entirely timber’ and ‘composite’ or ‘mixed’ materials, including amalgamations like timber with concrete or with steel, or combinations of timber, concrete, and steel, as illustrated in Figure 6.

Space efficiency refers to efficient use of net floor area (NFA) in relation to GFA, a critical factor in maximizing financial returns. Achieving high spatial efficiency depends on various elements, including structural and architectural design choices, elaborated upon in Appendix C. In this paper, space efficiency was assessed by calculating two percentages: NFA to GFA and core area to GFA [48,49,50,51,52,53,54,55,56,57,58,59]. NFA, derived by subtracting service core area from GFA, represents the functional space devoted to activities, ignoring infrastructure and support services. This ratio computes how successfully floor area is utilized in real-world applications, highlighting the spatial distribution efficiency. Concurrently, the core-to-GFA ratio measures the percentage of GFA occupied by important amenities including elevators, and stairwells, providing insights into infrastructure allocation and its impact on overall space utilization efficiency.

3. Results

In this part, the essential components of architectural design that impact spatial efficiency—location, function, core configuration, and form—were analyzed. Moreover, the primary structural aspects, including systems and materials, were considered. The analysis also examined spatial efficiency and its interplay with different design elements.

3.1. Architectural Design Parameters

As seen in Figure 7a, Europe, acting as a forerunner in mass timber technology, enjoys many benefits that establish it as leading worldwide center for tall timber projects. This prominence results from various issues. First, Europe possesses well-managed forests, guaranteeing a dependable timber supply, which is crucial for mass timber building [95]. Furthermore, the region has a robust framework of strict green policies, highlighting a promise to eco-friendly construction practices [96]. These favorable conditions contribute to Europe commanding a significant 70 percent share of the global market for high-rise timber edifices.

This study predominantly found that 65% serve residential purposes, 29% are in office use, and 6% are characterized as mixed-use and hotel buildings, as illustrated in Figure 7b and detailed in Appendix B. On the other hand, Figure 7c shows that the central core was used most frequently, making up 58% of the cases. This choice is due to its compact design, important role in the structure, ability to allow flexible façade designs, and fire safety. These aspects make it the best option among core designs. Moreover, external and peripheral cores are less common, likely because they have drawbacks like prolonged fire escape paths. Figure 7d underlines the popularity of prismatic configurations. The simplicity of these forms makes construction easier and more efficient, reducing complexity in building processes and cutting costs. They also optimize interior space with their straightforward layouts, making room arrangements more efficient and minimizing wasted areas.

3.2. Structural Design Parameters

As presented in Figure 8a, shear walled frame systems were the most used, at over 60%, followed by shear wall systems at 28%. Shear walled frame systems combine the flexibility of frame structures with the rigidity of shear walls, providing enhanced resistance to horizontal forces [97]. This dual benefit ensures that buildings can withstand significant stress without compromising structural integrity. Additionally, shear walled frames optimize material usage, offering cost efficiency without sacrificing safety or performance. Their integration into high-rise timber construction not only improves durability but also maximizes usable space within the building, making them a practical and effective choice for architects and builders. On the other hand, Figure 8b shows the dominance of the composite approach, making up 54% of the dataset, with timber accounting for 46%. The strategic integration of timber with other materials is vital for achieving several key objectives [98,99,100,101]. These initiatives involve lowering carbon emissions, enhancing construction efficiency, and swiftly delivering critical housing to accommodate the rapidly urbanizing global population.

3.3. Space Efficiency

In this study, average spatial effectiveness and core-to-GFA ratio were 84% and 10%, respectively. These quantities spanned from the lowest values of 70% and 4% to the highest values of 95% and 21%, respectively.

Table 1. Average space efficiency and ratio of core-to-GFA of different towers.

	Findings	Tall Timber Residentials (51 Cases)	Tall Timber Offices (33 Cases)	Non-Timber Mixed-Use Skyscrapers (64 Cases)	Non-Timber Residential Skyscrapers (27 Cases)	Non-Timber Office Skyscrapers (44 Cases)	Non-Timber Hotel Skyscrapers (31 Cases)
Average space efficiency	84% (ranges from 95% to 70%)	83% (ranges from 93% to 70%)	88% (ranges from 95% to 75%)	71% (ranges from 84% to 55%)	76% (ranges from 84% to 56%)	71% (ranges from 82% to 63%)	81% (ranges from 94% to 70%)
Average ratio of core to GFA	10% (ranges from 21% to 4%)	10% (ranges from 21% to 4%)	10% (ranges from 19% to 4%)	26% (ranges from 38% to 16%)	19% (ranges from 36% to 11%)	26% (ranges from 36% to 15%)	16% (ranges from 28% to 4%)

demonstrates results on the space efficiency and core-to-GFA of tall timber towers [48,49] and non-timber skyscrapers [51,52,53,56].

Apex Plaza, T3 Sterling Road Building 5A, 25 King, INTRO Residential Tower, and 77 Wade stand as paragons of contemporary architectural excellence, showcasing significant developments in spatial utilization, with remarkable efficiencies ranging from 93% to 95%. These projects establish a new industry standard by achieving the lowest core-to- GFA rate, as demonstrated in Appendix C. This extraordinary case is driven by thoroughly designed cores that emphasize compactness through optimization of service zones and shaft configurations, thus increasing the usable floor area. The strategic design approach minimizes the footprint of non-leasable spaces, enhancing overall building efficiency and offering flexible, expansive floor plans. Additionally, these towers incorporate shear frame systems that significantly enhance their structural rigidity against both vertical and lateral forces. This system uses compact cross-sections of load-bearing components to effectively resist loads, guaranteeing stability and safety. By integrating these advanced design principles, these buildings not only achieve superior space efficiency but also embody a commitment to sustainable urban development.

3.4. Relation of Space Efficiency and Main Design Considerations

Figure 9, Figure 10, Figure 11, Figure 12 and Figure 13 shows the existing links between architectural and structural elements related to spatial use, taking into account different functions. The bar charts on the right show the total number of structures sorted by their respective categories according to their respective functions. Colored markers show the spatial efficiency of towers relative to specific design elements. Additionally, bars represent the incidence of cases showing the same design elements within the sample.

As illustrated in Figure 9, average spatial efficiencies for the 79 analyzed towers are as follows: 83% for 51 residential units and 87% for 23 office structures. The limited number of hotel and mixed-use instances prevented the calculation of an average for those categories. The efficiency metrics span from 70% to 93% for residential buildings and 75% to 95% for office projects.

As depicted in Figure 10, a central core was the principal choice, represented by 46 buildings in the dataset. These cases exhibited spatial efficiency values between 71% and 95%, with a mean efficiency of 84%. Peripheral configurations, consisting of 31 buildings, showed space efficiency percentages 70–93%, with an average efficiency of 84%. Therefore, no difference is apparent between the two core configurations.

As shown in Figure 11, a prismatic form was dominant tendency, appearing in 64 cases. These types displayed space efficiency rates between 70% and 95%, with an average of 84%. Conversely, the combined total of cases featuring free and tapered forms amounted to 15 instances.

In Figure 12, shear walled frames represent the leading structure, appearing in 48 cases. These systems exhibited spatial efficiency between 75% and 94%, with an average of 85%. Towers with a shear wall system, accounting for 22 instances, showed an average of 80%. Thus, there is a 5% difference between the two core configurations.

As seen in Figure 13, timber and composite materials are primarily employed. Timber and composite demonstrate efficiency values varying between 70% and 94% as well as 75% and 95%, with average values of 83% and 85%, respectively. Therefore, the average spatial efficiency difference between the two predominant structural materials in the dataset is merely 2%.

4. Discussion

This article focuses on assessing the spatial efficiency of high-rise timber towers globally, addressing gaps identified in previous studies. By scrutinizing data from 79 cases, the authors identified crucial aspects that influence spatial efficiency. The primary findings of this investigation are as follows: (a) residential, central core, and prismatic configurations are predominant design considerations; (b) concrete is the most favored structural material, accompanied by shear walled frames as the preferred structural system; (c) the average spatial efficiency and percentage of core area to GFA were recorded at 84% and 10% with a range from the lowest values of 70% and 4% to the highest values of 95% and 21%, respectively.

In contemporary high-rise timber edifices, a central core layout is predominantly used; this a trend is supported by extensive research [50,51,52,53] and reflective of a wider architectural and construction preference. This core design improves structural stability, increases floor area efficiency by centralizing circulation and service facilities, ensures effective vertical transportation, and facilitates architectural flexibility, which is markedly advantageous in mixed-use towers. In this paper, most buildings feature a prismatic configuration, chosen for its simplicity [51,53]. These configurations are compatible with traditional building methods, facilitating project implementation. Their regular floor plans enhance spatial use and operational efficiency, making room outlines straightforward for inhabitants.

A distinct hierarchy has developed within structural systems of wooden buildings, with high-rise timber projects predominantly utilizing shear walled frames due to their enhanced stability against lateral loads. An emerging inclination in high-rise timber construction is the growing acceptance of timber and concrete composite materials, which have become the favored choice due to their adaptability and multiple benefits [102]. This hybrid approach leverages the aesthetic warmth and appeal of timber along with the strength and versatility of concrete [103,104,105].

A recommended benchmark for assessing space efficiency of high-rise edifices is achieving 75% [106]. Research on non-timber skyscrapers discovered varying degrees of space use, typically fluctuating between 71% and 81% [51,52,53,56]. These studies highlight significant variations in the percentage of core area to GFA, varying between 16% and 26%. Furthermore, research involving 55 timber Finnish dwellings demonstrated space utilization rates spanning between 78% and 88%, with an average efficiency of 83%. Additional papers focusing on high-rise timber residential and office structures indicated space efficiencies fluctuating between 70% and 93% as well as 75% and 95%, respectively, with average efficiencies of 83% and 88%. Within this article, the average space use rate was determined to be 82%, while the core area to GFA percentage averaged 11%. Here, the lowest space efficiency was recorded at 70% and the highest at 90%, and the core area to GFA varied between 4% and 21%. These findings highlight the importance of optimizing the core design and spatial layouts to improve high-rise building efficiency. Adhering to these standards can enhance the functionality of both timber and non-timber structures, supporting more sustainable and economically viable urban environments, and advancing modern architectural practices.

The pronounced difference in space efficiency between wooden and non-wooden tall towers stems from intrinsic variances in their material properties and building practices [107,108,109]. Timber edifices exploit the advantages of lightweight frames, allowing for the use of slender structural components. This stands in stark contrast to the thicker and heavier components required in concrete or steel buildings. The integral lightness of timber facilitates the construction of thinner walls, efficiently enhancing the usable floor area within a given building footprint. Furthermore, timber’s exceptional strength-to-weight ratio supports longer spans and reduces the need for numerous internal supports, thereby increasing inner design flexibility and optimizing spatial utilization. Conversely, non-timber systems like concrete necessitate bulkier load-bearing members to achieve comparable structural capacities. This results in the construction of thicker walls and deeper floor sections, which characteristically reduce the efficiency of usable space. In addition, the heavier weight of concrete and steel demands more substantial foundations and support structures, further encroaching on the available interior space. Thus, the fundamental material and structural differences between wooden and non-wooden systems lead to significant variations in spatial efficiency, with timber offering superior optimization of interior layouts and greater overall useable floor area.

Future research on space efficiency can explore several key areas [110,111,112]. Prefabrication and modular construction techniques offer the potential for more efficient assembly and space maximization [113,114,115]. Advances in engineered timber products and nanotechnology could lead to slimmer, stronger structural profiles [116,117,118]. Architectural innovations, such as adaptable layouts and vertical green spaces, can greatly improve space efficiency and quality of life [119,120,121]. Sustainability research, including life cycle assessments and carbon sequestration strategies, is crucial for advancing timber construction’s environmental benefits [122,123,124]. Building performance studies focusing on fire safety, seismic resilience, and smart technologies can enhance safety and efficiency [125,126,127]. Economic analyses and policy advocacy are essential for promoting high-rise timber construction, supported by research on health, well-being, and cultural acceptance [128,129,130].

5. Conclusions

This study enhances the understanding of design features influencing spatial efficiency in high-rise timber structures, an increasingly relevant sector due to its environmental and economic advantages. Through the analysis of 79 global cases, key architectural and structural preferences were identified, including the predominance of residential functions, centrally located service cores, and prismatic building forms, all of which contribute to optimized spatial efficiency. The results highlight the frequent use of composite materials and shear-walled frame systems, with an average spatial efficiency of 84% and a core area percentage of 10% relative to GFA. Notably, this paper found that when appropriately planned, variations in core design, building form, and structural material do not significantly impact spatial efficiency, suggesting a level of flexibility in design choices.

Based on these findings, it is recommended that architects and engineers prioritize the use of centrally located service cores and prismatic building forms in the design of high-rise timber structures to maximize spatial efficiency. Additionally, the adoption of composite materials and shear walled frame systems is advised to further enhance the effective use of space within these buildings. This strategic focus can help optimize both the functional and feasibility of high-rise timber construction.

It is essential to recognize limitations inherent in the research. First, the sample size of 79 cases, although informative, may not fully capture the diversity and variability of high-rise timber structures globally, potentially restricting the generalizability of the results. Second, this research is cross-sectional, relying on existing buildings, which may not reflect emerging trends or future innovations in timber construction. This temporal limitation restricts the ability to assess how design preferences and spatial efficiency might evolve over time. Future research should aim to address these limitations by increasing the dataset to incorporate a wider range of cases and incorporating longitudinal studies to observe the long-term effects of design choices on spatial efficiency in high-rise timber structures.