Section 1 Wood Construction

#### **Chapter 1**

## Massive Wood Construction in Finland: Past, Present, and Future

*Hüseyin Emre Ilgın and Markku Karjalainen*

#### **Abstract**

Finland has a long history of massive wood construction such that the log construction technique has been used as a traditional method of Finnish residential construction for thousands of years, and the entire history of Finnish architecture is based on this technique. Today, almost all leisure buildings, for example, cottages in Finland are made of wood and mostly log construction. Also, today 90% of Finland's detached houses have timber frames, and a quarter of them are made from industrial glue logs. Apartment buildings began to be made of wood, especially cross-laminated timber (CLT) and laminated veneer lumber (LVL). The most common way of constructing wooden apartments is to use volumetric elements as compared to load-bearing large elements and post-beam systems. The increase in environmental awareness in Finland, as in many European countries today, strengthens the popularity of wood construction, and this brings the search for innovative and environmentally friendly engineered wood product solutions (e.g., dovetail massive wood board elements) as a future vision. The chapter aims to identify, combine, and consolidate information about massive wood construction in Finland from past, present, and future perspectives. This study will assist and guide Finnish key professionals in the design and implementation of timber buildings.

**Keywords:** timber/wood, construction, log construction, engineered wood products, sustainability, dovetail massive wooden board elements, Finland

#### **1. Introduction**

Finland has a long history of using massive wood in construction, starting with thousands of years of log building techniques [1]. Log, which was traditionally carved by hand from single trees, has been the main material of all types of buildings, for example, residences and religious buildings. In the early phases of industrialization, the log was used merely for the construction of sauna huts and summer cottages (**Figure 1**) [2–4]. Today's logs are produced industrially in factories, using sophisticated woodworking machines from glued laminated wood (**Figure 2**) [5]. Moreover, in the last 10 years, log construction doubled the share of all new prefabricated detached houses sold in Finland [6]. Overall, there is a swift development going on right now, where the use of log construction is growing, and neither the usage context of the logs nor the log itself is the same as in the past [7].

**Figure 1.** *Log cottage example from Finland (photo courtesy of Lotta Häkkänen).*

**Figure 2.** *A modern log cottage example from Finland (photo courtesy of Lotta Häkkänen).*

#### *Massive Wood Construction in Finland: Past, Present, and Future DOI: http://dx.doi.org/10.5772/intechopen.104979*

Finland has been experimenting with wood-frame multi-story construction since the mid-1990s due to industrialized prefabrication of engineered wood products (EWPs) such as CLT, and LVL [8], which allowed the use of wood in large-scale construction, for example, multi-story apartment buildings [9]. Furthermore, as timber construction research has increased in Finland in recent years, the use of EWPs in the construction sector has become gradually more prevalent (e.g., [10–12]). The most popular way of constructing wooden apartments is to use volumetric elements as compared to load-bearing large elements and post-beam systems [13]. Here, wooden multi-story refers to buildings more than 2-story with a wooden structural frame and, in some cases, with timber facade cladding [14, 15]. Moreover, the Finnish fire code was revised so that residential and office buildings with timber structures and facades could rise to 4-story and then 8-story in 1997 and 2011, respectively [16]. With the revision in 2018, it has become possible to design and construct housing and office buildings with timber structures and facades up to 8-story and, due to functional fire planning, wooden buildings higher than 8-story (e.g., apartments, dormitories, hotels, and offices) are also possible [17]. Currently, there are two wooden tall residential buildings (≥9-story), 14-story Lighthouse Joensuu (2019) with LVL (**Figure 3**), and 13-story HOAS Tuuliniitty (2021) with CLT (**Figure 4**).

In line with "Finnish National Energy and Climate Strategy" [18] and "Guidelines on State Aid for Climate, Environmental Protection and Energy 2022" [19], as a reflection of environmentally friendly approaches to reduce greenhouse gas emissions and carbon footprint on the construction industry, the use of wood has become more prevalent, especially by being encouraged by many government-supported

**Figure 3.** *Lighthouse Joensuu (photo courtesy of Arcadia).*

institutions, organizations, and regulations in Finland [20–28]. As a result, the search and trend towards innovative and "green" wood products such as adhesive- and metal fastener-free dovetail wood board elements (**Figure 5**) seem to shape the future of the Finnish construction industry [29, 30].

Overall, this chapter examines massive wood construction in Finland from past, present, and future perspectives. It is thought that this study will assist and guide key professionals in the design and implementation of timber buildings in Finland.

#### **Figure 5.**

*Test specimen of adhesive- and metal fastener-free dovetail wood board element (photo by Hüseyin Emre Ilgın).*

The chapter is structured as follows. The next section presents Finnish massive wood construction by detailing the history of log-based wood construction, the current state of the art, and finally the future of the Finnish wood construction industry. The last section provides our concluding remarks.

#### **2. Massive wood construction in Finland**

#### **2.1 Past**

The entire Finnish wooden building tradition is based on the use of logs (**Figure 6a**). The art of building logs has been developing in the northern coniferous region for more than a thousand years. The log structure is a traditional wooden construction method in which load-bearing walls are made of logs. In Finland, logs are usually arranged horizontally and joined by special corner joints (**Figure 6**) [31]. The horizontal log technique, which resulted in simple rectangular building volumes with scale uniformity relative to the length of the log, has been used in Finland for over a thousand years. Due to the always availability of trees, logs have become a natural building material in Finland.

In the first decades of the twentieth century, a new American-style lightweight timber-frame construction system began to be used in Finland [32] and log construction was the most used practice for residential buildings until the 1930s before the dominance of the American light frame in Finnish wooden construction industry [33].

In the 1930s, the Finnish forest, used for the paper and timber market, contributed to the industrialization of the country. In this period, when the international

#### **Figure 6.**

*Log construction (a) earlier corner detail (photo courtesy of Lotta Häkkänen) and (b) modern corner detail (photo by Hüseyin Emre Ilgın).*

style influenced Finnish architects, the Finnish wooden building tradition was heavily applied [34]. Rising labor costs spurred single-home builders to seek alternatives for industrial-scale housing solutions. The American-style urbanization and industrialization at the time gave architects like Alvar Aalto, designing numerous multi-dwelling accommodation facilities, enough inclination to explore possibilities including prefabricated solutions [35]. The focus of the construction was solely derived from natural resources, for example, the abundance of Finnish forests. Single houses were built utilizing massive wood logs harvested directly on the site [36].

In the 1940s, World War II led to a shortage of building materials and a demand for community and residential construction in a timely and cost-effective way. It's worth noting here that Alvar Aalto's approach relied on the use of prefabricated elements specifically to maximize Finland's use of forest resources, as a continuation of the framing system experiment Finland modeled on its previous American predecessor [34]. Nevertheless, despite heavy investments and the overall positive impact of the practice on Finland's architectural development, adverse weather conditions, and high labor costs resulted in low participation in this practice.

The arrival of wooden facades coincided with the end of World War II. The peculiarities of prefabrication during the war, especially due to the fast pace of construction, cemented the position of this private residential solution in Finnish construction history. Prefabrication provided an effective solution to the population boom, rapid urbanization, and migration from more rural areas to urban centers in Finland. Finnish log construction took on new vitality in the early 1950s, with the industrial production of log houses (**Figure 6b**). Due to their nail-free structure and good availability of timber, logs were again a beneficial building material, which was mostly used in single-family houses. On the other hand, with the emerging modernist movement internationally, concrete flourished on the construction scene in the late 1960s and became a generally common material for medium to large-scale building designs.

In the early 1990s, Finland started a piloting effort to explore the potential to return to wood construction, which was a background indicator of the relevance of Finnish buildings to traditional Finnish cultural values and the return to deindustrialization. However, although this effort was reflected in several pioneering projects that promoted the validity of wood as the next major building material, it later lost power due to the general economic fluctuation at the national level. Even though the economic boom of the late 1990s greatly boosted development in the construction industry, the American platform framing technique had a chance to enter the timber construction market as the forestry industry did not have a vision of collaborating particularly with architectural and structural designers to compete with concrete practices in Finland.

While the resulting pilot projects were successful, regulatory, and labor issues and logistical challenges combined with the disconnect between engineers and product manufacturers, the forestry industry's inability to provide the necessary technical assistance towards wood construction standards, and the lack of funding for further research and development, reduced the chance of wood to compete with the mature concrete industry [35].

The second wave of timber booms began in 2011 when an amendment to the Finnish fire code allowed wooden structures and facades to be used in projects, increasing the maximum allowable height of the building for wooden structures to 8-story.

*Massive Wood Construction in Finland: Past, Present, and Future DOI: http://dx.doi.org/10.5772/intechopen.104979*

#### **2.2 Present**

Regarding the log construction mentioned in the previous section, as is known, traditionally logs have been handcrafted from a single tree trunk, while modern logs are precise industrial products manufactured in plants by bonding together multiple parallels or cross lamellas of timber. As part of the global development of massive wooden construction, the use of industrial log construction has become more and more popular in Finland over the past decade (see **Figure 7**) [37] such that from just over 10% a decade ago, now about 30% of all new single-family homes have log structure [38].

Recent buildings using industrial logs show that this reputation also applies to larger construction, for example, school campuses (**Figure 8**). Additionally, in the early 2000s, due to the poor architectural quality of industrially produced log buildings, there were attitudes among designers and construction officials towards the use of logs in urban or suburban contexts, however, particularly in the last decade, the perception that log structures have an untapped potential for architectural expression has positively changed the perspective of professionals [39].

Wooden multi-story construction has been on the Finnish national policy agenda since the 1990s and there are high expectations for its potential market growth [40]. Additionally, in particular, due to the revision made in the Finnish fire code in 2018, it has been possible to design and construct residences, dormitories, hotels, nursing homes, offices with wooden structural systems up to 8-story, and buildings with more than 8-story, functional fire design analysis is applied in Finland.

Finland has the second-highest proportion of multi-story buildings in Europe after Spain, and about 47% of Finnish housing units are located in multi-story buildings [41]. However, the market share of timber multi-story apartments constructed was only 1% in 2010, and the share increased to 10% by 2015 [42]. By March of 2022, 130 two-story timber apartment buildings have been built in Finland, a total of 4150 apartments [43, 44].

**Figure 7.** *A four-story log apartment, Finland (photo by Hüseyin Emre Ilgın).*

**Figure 8.** *Pudasjärvi log school campus, Finland (photo by Hüseyin Emre Ilgın).*

The American platform-frame system, based on floor-by-floor stud frame construction, was mostly used for the construction of Finland's earliest residential buildings. Nowadays, in Finland, timber apartments are executed with three different structural solutions: a volumetric modular system, a load-bearing large element system, and a post-beam system, and among them, the most popular way of building wooden apartments is to use of volumetric modular element designs based on CLT [45]. On the other hand, these elements can also be applied as a rigid structure. Furthermore, timber-concrete composite board structures are primarily utilized on the intermediate floors due to their advantage in sound insulation.

Besides wooden construction in Finland, interest in high-rise construction has also risen over the past decade, which is mostly related to the urbanization trend in Finnish major cities as in other metropolises of the world [46–50]. In this sense, multi-story timber construction has been endorsed in Finland since the 1990s [51], and multi-story and tall buildings are considered the biggest opportunity for growth in wooden construction [52] with national policy support [53], as in the 14-story Lighthouse Joensuu (**Figure 3**) and 13-story HOAS Tuuliniitty (**Figure 4**), and the 8-story high Puukuokka 1.

On the other hand, due to the separation of the market by construction systems, difficulties arose when potential industry partners tried to enter the market, as the solution for each construction system was often different from the others. This challenge hindered the progress of the industry by discouraging potential competitors. Various strategies have been documented and introduced concerning the current market situation, both from a national programming perspective and as an internal review of possible policies.

Running various programs across the country to focus on the use of natural resources, from micro to macro scale, the Finnish government has been a supporter of the timber industry in general, putting wooden apartments on the national programming agenda. Alongside efforts to standardize construction systems, supporting activities in the industry have been undertaken by individual and government agencies.

Moreover, according to studies such as policy gap analysis of programs promoting the use of timber in construction in the Finnish context [54], the following are considered among the main obstacles and challenges: (i) demand for stricter fire safety measures compared to traditional building materials; (ii) lack of support from municipalities on tenures for new buildings; (iii) different practices and additional fee demands of insurance companies for timber structures; (iv) lack of knowledge about carbon footprint calculation methods, evaluation of operating and maintenance costs; (v) lack of suitable tools for implementing wood construction projects in BIM; (vi) training offer gap causing a shortage of available experts in the field; and (vii) skepticism about the durability of the material.

Overall, in the rapidly and constantly changing building construction industry, sustainable approaches often use specific materials and technologies to support architectural design. These strategies are also significantly influenced by the characteristics of the available market margin. Every major component in the market value chain must be scrutinized to give a healthy impetus to practical and profitable solutions in the industry. While Finland leads the way in joining the world race in environmentally-friendly applications, certain conditions in the Finnish construction sector tend to aggressively hinder progress. More specifically, the targeted level of using wood as the main building material in medium and large-scale projects has not been reached yet [35].

#### **2.3 Future**

As noted earlier, there is strong governmental support for timber construction in Finland, which is also defined in various national strategies and programs such as the Government Programme, the National Energy and Climate Strategy, the National Forest Programme, and the Finnish Bioeconomy Strategy, which aimed at increasing the share of long-term carbon storage products and applications. For example, The Wood Building Programme, which sets one of its goals as rising the market share of timber structures in public buildings to 30% in 2022 and 45% in 2025, has five focus areas: increasing the use of timber in urban development, endorsing the use of timber in public buildings, increasing the construction of large timber structures, reinforcing local skill bases, and encouraging exports [55].

In line with the government policy mentioned above, by focusing on the impact of business activities, for example, building construction industry, on climate and natural sources, ecological awareness has increased significantly in the last two decades and environmental degradation has been defined as a global problem (e.g., [56–58]). This important global rising awareness has led to the development of new and more environmentally friendly timber-based solutions, especially in the Finnish wood construction industry as the future vision. In this context, many research projects (e.g., the DoMWoB project/Dovetailed Massive Wood Board Elements for Multi-Story Buildings—see Acknowledgments and Funding) (**Figure 9**) [42, 59] are being carried out as in other EU countries (e.g., [60]).

In addition, as in other Scandinavian countries, the rise of wooden multi-story construction in Finland has become the most prominent new construction-related business opportunity in the emerging bio-economy. Similarly, the construction of tall timber buildings (≥9-story) seems to be gaining momentum, driven by decarbonization, forest management and timber life cycle, urbanization and densification, productivity in the construction industry, and benefits of using timber indoors [61, 62]. Moreover, in Finland, as part of the rise of the environmentally friendly building

#### **Figure 9.**

*Manufacture of dovetail massive wood board element at Vocational College Lapland (Ammattiopisto Lappia), Kemi, Finland (photo by Hüseyin Emre Ilgın).*

concept, the future of wooden construction can be shown as hybrid buildings, where other materials are used together and benefit most, either structural members (such as wood and steel or concrete combinations) or cross-section-based level (such as wood and plastic) [63]. As in the cases of the 25-story and 87 m high Ascent (Milwaukee, under construction), the 24-story and 84 m high HoHo (Vienna, 2020), and the 18-story and 58 m high Brock Commons Tallwood House (Vancouver, 2017), hybridization using a reinforced concrete core target better structural safety and performance, which becomes more and more important with increasing building height.

#### **3. Conclusions**

This study identifies, combines, and consolidates information about massive wood construction in Finland from past, present, and future perspectives. Finland has a long history of using massive wood in construction, starting with thousands of years of log building techniques. Wood-based solutions have traditionally held a strong position in Finland's construction industry and account for approx. 40% of all building materials. Today almost 90% of Finland's detached houses are timberframed, and a quarter of them are made from industrial glue logs. Wood is also used on construction sites in structures, windows, doors, and finished surfaces, as well as in formwork construction, among other uses. Apartment buildings began to be made of wood, especially CLT and LVL mostly with volumetric elements. In addition, the possibilities of using wood have been expanded to include renovations and extensions of suburban concrete apartments. There are significant activities, initiatives, and legalization in support of wooden structures concerning current European regulations emphasizing the use of wood as a sustainable architectural building material for the future in Finland.

#### **Figure 10.**

*Preparation of dovetail specimens for fire resistance test at Tampere University Fire Laboratory, Tampere, Finland. (a) Drilling and (b) thermocouple insertion (photos by Hüseyin Emre Ilgın).*

Overall, the global economy engine naturally shifted the focus of Finnish construction technology to viable solutions, which means that concrete's low return on value hinders the use of one of the defining features of Finland's global image—the vast forest resources are not fully utilized internally as they should be. In this sense, because of environmental considerations, there is a rising interest in the use of timber and the advancement of wooden structural elements. This has led to a wide variety of EWPs used in advanced ways to replace conventional construction materials, for example, steel and reinforced concrete, and enhance the appeal of wood construction, thus leading to the quest for groundbreaking and environmentally friendly EWP solutions (e.g., dovetail massive wood board elements) (**Figure 10**) for the future of timber in Finland. Currently, although the uptake of for example dovetail massive wood board elements for industrial applications is very limited, with new projects to be developed, it can be used more in the construction of multi-story and even tall buildings. In order to contribute to environmentally friendly construction and low embodied energy and carbon buildings, more research is needed to develop innovative and sustainable EWPs that are nontoxic, low-cost, recyclable with well-designed structural features and life cycle assessments.

This study will assist and guide Finnish key professionals in the design and implementation of timber buildings, highlighting the status and future directions of massive timber construction.

#### **Acknowledgements**

This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No [101024593].

### **Funding**

This project has also received funding (60,000 EUR) from the Marjatta and Eino Kolli Foundation for funding the technical performance tests including fire safety, structural, moisture transfer resistance and air-tightness, and sound insulation.

### **Author details**

Hüseyin Emre Ilgın\* and Markku Karjalainen Tampere University, Tampere, Finland

\*Address all correspondence to: emre.ilgin@tuni.fi

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Massive Wood Construction in Finland: Past, Present, and Future DOI: http://dx.doi.org/10.5772/intechopen.104979*

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[54] Maniak-Huesser M, Tellnes LGF, Zea Escamilla E. Mind the gap: A policy gap analysis of programmes promoting timber construction in nordic countries. Sustainability. 2021;**13**(21):11876

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[56] Sotayo A, Bradley D, Bather M, Sareh P, Oudjene M, El-Houjeyri I, et al. Review of state of the art of dowel laminated timber members and densified wood materials as sustainable engineered wood products for construction and building applications. Developments in the Built Environment. 2020;**1**:1-11

[57] Salvadori V. Multi-storey timberbased buildings: An international survey of case-studies with five or more storeys over the last twenty years [PhD dissertation]. Vienna, Austria: Technische Universität Wien; 2021

*Massive Wood Construction in Finland: Past, Present, and Future DOI: http://dx.doi.org/10.5772/intechopen.104979*

[58] Svatoš-Ražnjević H, Orozco L, Menges A. Advanced timber construction industry: A review of 350 multi-storey timber projects from 2000- 2021. Buildings. 2022;**12**(4):404

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[60] Rinne R, Ilgın HE, Karjalainen M. Comparative study on life-cycle assessment and carbon footprint of hybrid, concrete and timber apartment buildings in Finland. International Journal of Environmental Research and Public Health. 2022;**19**:774

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[62] Ilgın HE, Karjalainen M. Preliminary design proposals for dovetail wood board elements in multi-story building construction. Architecture. 2021;**1**:56-68

[63] Ilgın HE, Karjalainen M, Koponen O. Various Geometric Configuration Proposals for Dovetail Wooden Horizontal Structural Members in Multistory Building Construction. London, UK: IntechOpen; 2022

#### **Chapter 2**

## Tallest Timber Buildings: Main Architectural and Structural Design Considerations

*Hüseyin Emre Ilgın and Markku Karjalainen*

#### **Abstract**

Since the end of the twentieth century, the question of how to deal with the increasing scarcity of resources has been at the center and the need for renewable materials has come to the fore, especially in the construction sector. A possible solution to these environmental challenges is represented by the development of engineered timber products, which allowed the realization of tall timber structures. Their main drivers are decarbonization, forest management, and timber life cycle, urbanization, and densification, productivity in the construction industry, and the benefits of using timber indoors. In this context, this chapter will analyze data from the 10 tallest timber building cases to enhance the understanding of contemporary trends. Data are collected through literature surveys and case studies to analyze the main architectural and structural design concerns to contribute to the knowledge about the growing tall timber structures around the world. By revealing up-to-date features of the tallest timber towers, it is thought that this chapter will contribute to aiding and directing key construction professionals such as architects, structural engineers, and contractors, in the design and construction of future tall timber building developments.

**Keywords:** timber/wood, engineered timber/wood products, tall building, timber construction, architectural design considerations, structural design considerations, dovetail massive wooden board elements

#### **1. Introduction**

The utilization of timber in the construction sector has been revived since the mid-1990s [1, 2], and particularly in the last 10 years [3, 4], due to environmental concerns, urbanization challenges, and productivity in the construction industry [5–7]. Since the end of the twentieth century, the question of how to deal with the increasing scarcity of resources has been at the center and the need for renewable (building) materials has come to the fore, especially in the building construction industry [8]. A potential solution to these challenges is the development of engineered timber products (ETPs) that enable the erection of tall timber buildings [9] as in the case of the 18-story and 85 m high Mjøstårnet (Brumunddal, 2019).

CO2 has been a game-changer since 1970, sparking a revolution in the way buildings are built. With the successful implementation of issues such as efficiency and passive standards in just a few years, there has been an increased emphasis on sustainability during and after the construction site [10]. Furthermore, today, the construction industry accounts for approximately 40% of annual greenhouse gas emissions, 40% of global resource consumption, 40% of energy use, and 50% of global waste, timber is a valuable alternative material [11, 12].

In this sense, the use of timber can enable the construction industry to avoid significant greenhouse gas emissions associated with unsustainable material use, as it is a natural carbon sink [13]. In other words, the fact that it is a renewable building material that can store CO2 compared with steel and concrete, which are traditional building materials, has brought timber to an important point as a construction material [14, 15].

On the other hand, simultaneously, the world population doubled in less than a century, and for the first time in history, more people lived in cities than in the countryside [16]. The overall effect of this high density of people in cities forced buildings to rise. However, combined with the chronically low productivity of the construction sector since the 1990s and the high demand for new buildings in the future [17], there may be other challenges to reducing greenhouse gas emissions. The assessment of a skilled and aging workforce and slow construction time, among other factors, are significant challenges for both established and future companies [18]. Prefabrication is recommended as the best way to improve productivity, and timber is perfectly suited for this as it is light and easy to work with [19, 20].

Latest technical developments in ETPs (e.g., [21]) and systems, as well as regulatory procedures in fire codes, other building codes, and various government regulations initiatives, have allowed timber construction to reach new heights [22]. Multistory construction is a new and promising business with high potential to support the bioeconomy [23] as in the case of the 25-story and 87 m high Ascent (Milwaukee, under construction) (**Figure 1**). Besides the potential for substantial

**Figure 1.** *Ascent (image courtesy of Jason Korb/Korb + Associates Architects).* *Tallest Timber Buildings: Main Architectural and Structural Design Considerations DOI: http://dx.doi.org/10.5772/intechopen.105072*

environmental and economic life cycle advantages can contribute to social sustainability in the processing of materials, as in both primary production and timber-based value chains [24].

In the literature, numerous surveys present the technical features of ETPs, their use in building construction, and diverse technical solutions (e.g., [25–28]). Several surveys focus on timber as a construction material from the viewpoints of key specialists (e.g., [29–32]) and users or inhabitants (e.g., [33, 34]); whereas there is a very limited number of comprehensive comparative design studies on architectural and structural parameters of multistory and tall timber buildings (e.g., [35–37]).

This chapter aims to identify, organize, and combine the data about the tallest timber buildings from the primary architectural and structural aspects to enhance understanding of the design and construction of these towers. To accomplish this goal, data were collected from the 10 tallest timber buildings under construction and completed.

The scope of the chapter is limited to the information available and uses key points to provide a representative understanding of contemporary trends in tallest timber buildings: general information (building name, location, height, number of stories, completion, gross floor area, amount of timber used), architectural and structural design parameters (building form, core type, structural system, and material). It is thought that this study will contribute to aiding and directing architects in the design and construction of future tallest timber towers.

#### **2. Materials and methods**

The chapter was mainly conducted through a literature review including peerreviewed research, official documents and reports, fact sheets, architectural and structural magazines, and other Internet sources. Additionally, case studies were used to identify, gather, and combine the data about the tallest timber buildings to examine the architectural and structural perspectives. The study sample included 10 tallest timber buildings under construction and completed, in a variety of countries (two from Norway, two from Finland, two from Canada, one from Austria, one from the Netherlands, one



*Note on abbreviation: 'UC' indicates under construction; 'NA' indicates not available; 'CLT' indicates cross-laminated timber; 'GL' indicates glue-laminated timber; 'PSL' indicates parallel strand lumber.\* Different levels and kinds of data for "the amount of timber" e.g. structural timber, entire construction, or only CLT were given by various references.*

#### **Table 1.**

*10 tallest timber buildings.*

from the United Kingdom, and one from the United States) as seen in **Table 1**. In the study, a "tall building" was defined as a building with over eight story [22].

In terms of functionality, tall buildings can be classified as single-use or mixeduse. In this study, hotel, residence, and office were considered as primary functions, whereas their combinations were considered mixed-use. Taking into account existing literature (e.g., [36–43]), the classifications based on their structural behavior under lateral loads by Ilgın [44–46] and Ilgın et al. [47] were used in this paper due to its more comprehensive and clearer structures (see **Table 2**).


#### **Table 2.**

*Core, building form, structural system, and structural material classifications.*

*Tallest Timber Buildings: Main Architectural and Structural Design Considerations DOI: http://dx.doi.org/10.5772/intechopen.105072*

#### **3. Findings: main architectural and structural design considerations**

As can be seen in **Table 3**, the case study buildings were designed mostly for residential purposes, and the two mixed-use cases also included residential use. Additionally, central core arrangement was the dominant core typology (only one case with peripheral core). The benefits of a central core are factors, e.g., structural contribution, compactness, making the exterior facade open to light and scenery, and facilitating fire escape, which can aid in the dominant formation of this typology.

Prismatic forms were the most common and occurred in eight case studies including HoHo (**Figure 2**). The reason why prismatic forms are common may be due to ease of workmanship, practicability, and efficient use of interior space (especially in rectangular floor plans) compared with complicated forms.

The advantages of shear wall systems in buildings up to approximately 35 stories such as construction speed, suitability for prefabrication, and sufficient rigidity to withstand lateral loads may be the reasons behind this occurrence [48] as in the case of the 22-story and 73 m high HAUT (Amsterdam, 2022) (**Figure 3**) with a concrete


#### **Table 3.**

*Tallest timber buildings by function, core type, form, structural system, and structural material.*

#### **Figure 2.**

*HoHo (photo courtesy of DERFRITZ).*

core and CLT shear walls. Additionally, Mjøstårnet (**Figure 4**) and Treet took the advantage of trussed-tube system, in which exterior multistory GL trusses handle the horizontal and gravity loads to ensure the required rigidity of the structure and the CLT core has a nonstructural function [49, 50].

On the other hand, the interstory drift between adjacent floors of upper stories in shear wall systems and the interstory drift between adjacent floors of lower stories in rigid frame systems are problematic issues, but shear frame systems (namely shear trussed frame and shear-walled frame systems) offer a solution where both systems compensate for each other's disadvantages as in the case of the 18-story and 58 m high Brock Commons Tallwood House (Vancouver, 2017) (**Figure 5**).

In terms of structural material, CLT was the structural material commonly used in 10 selected cases (**Table 3**). In the buildings where composite/hybrid systems were employed, concrete was utilized in all four cases. Additionally, in all case studies, the ground floor or podium was made of concrete and had a reinforced concrete core. Moreover, among them, in Ascent, mass timber residential floors were built over 5-story-concrete parking. Concrete podium construction has many advantages, including ground-level housing facilities and services, offering high clearances in public areas and large openings, and creating fireproof zones for primary mechanical *Tallest Timber Buildings: Main Architectural and Structural Design Considerations DOI: http://dx.doi.org/10.5772/intechopen.105072*

**Figure 3.** *HAUT (photo courtesy of Jannes Linders).*

#### **Figure 4.**

*Mjøstårnet (photo courtesy of Voll Arkitekter AS + Ricardo Foto).*

and electrical components [51]. Furthermore, the reason for employing concrete core: (i) to provide the lateral rigidity and strength of the structure to a great extent; (ii) to take advantage of the natural resistance of concrete against fire; (iii) to benefit from

**Figure 5.** *Brock Commons Tallwood House (photo by Michael Elkan and courtesy of Acton Ostry Architects).*

its advantage in damping wind-induced building sway, which is one of the commonly confronted issues in high-rise buildings [52].

#### **4. Concluding remarks**

Driven predominantly by decarbonization, forest management, and timber life cycle, urbanization and intensification, and productivity in the construction industry, tall timber buildings have been at the forefront of construction practices in the global urban context for over one decade with an ever-increasing trend of height. It is thought that the analysis of the key architectural and structural design concerns of the 10 tallest buildings (one is under construction) will contribute to the planning of future timber buildings that will push the height limits.

The tallest timber buildings were mostly designed as residential. Central core arrangement was the dominant core typology. Prismatic forms were most widely used. Shear wall systems were preferred in five cases. In terms of structural material, six cases used pure wood, mostly CLT, while others opted for composite, usually concrete.

#### *Tallest Timber Buildings: Main Architectural and Structural Design Considerations DOI: http://dx.doi.org/10.5772/intechopen.105072*

Rules, expectations, requirements, and typologies for tall wooden buildings, whose design dynamics are associated with technological developments and new construction techniques, have not yet been clarified. The diversity in the design and construction methods of these structures is still evolving to meet various building codes, market demands, contexts, and environments. This chapter has given the most up-to-date information on this pioneer building typology.

This report also has its limitations, since the empirical data presented in this chapter were limited to 10 buildings, it seems difficult to generalize about timber tall buildings of the future. On the other hand, given the increase in the number of tall timber buildings erected, further research can be conducted with larger sample groups to obtain broader generalizations and new information.

Additionally, the increase in global environmental awareness strengthens the attractiveness of timber construction, which leads the search for innovative and environmentally friendly engineered timber product solutions such as the DoMWoB

**Figure 6.**

*(a) Dovetail massive wood board prototype manufactured at Vocational College Lapland (Ammattiopisto Lappia), Kemi, Finland; (b) Fire test specimens mounted to supporting construction made of aerated concrete blocks at Tampere University Fire Laboratory, Tampere, Finland (photos by Hüseyin Emre Ilgın).*

project (Dovetailed Massive Wood Board Elements for Multi-Story Buildings); see Acknowledgments and Funding (**Figure 6**) [53] in the future. Although for example, the uptake of dovetail massive timber elements for industrial applications is very limited at the moment, with new research projects to be developed, these elements can be used more in multistory and even tall building construction.

#### **Acknowledgements**

This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No [101024593].

#### **Funding**

This project has also received funding (60,000 EUR) from the Marjatta and Eino Kolli Foundation for funding the technical performance tests including fire safety, structural, moisture transfer resistance and air-tightness, and sound insulation.

### **Author details**

Hüseyin Emre Ilgın\* and Markku Karjalainen Tampere University, Tampere, Finland

\*Address all correspondence to: emre.ilgin@tuni.fi

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Tallest Timber Buildings: Main Architectural and Structural Design Considerations DOI: http://dx.doi.org/10.5772/intechopen.105072*

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#### **Chapter 3**

## Sustainable Wooden Skyscrapers for the Future Cities

*Amjad Almusaed and Asaad Almssad*

#### **Abstract**

At the time of writing, energy-saving and eco-friendly building materials have gained acceptance, recognition, and a strong foothold in the construction sector. There is an appreciable degree of congruence in the development of green buildings and bio-based building materials, making it imperative to promote and sustain the application of such materials. Wood is endowed with a host of favorable properties sought after in a building material—its organic warmth, softness, ability to control indoor moisture levels and act as a good insulator, malleability, and workability, to name a few. Wooden buildings blend perfectly into the surrounding landscapes much better than their counterparts. It facilitates design for lightweight and strength, is a renewable resource, and accords stability and seismic resistance to structures. The focus of this chapter is on wooden skyscrapers which promise to be a greener and ecofriendlier option vis-à-vis the conventional concrete high-rises.

**Keywords:** bio-based materials, eco-friendly building materials, sustainable buildings, wooden skyscrapers

#### **1. Introduction**

Modern architecture is changing the face of megacities, creating a more comfortable and prosperous environment for life. Leading architects are increasingly choosing those forms and materials that increase the energy efficiency of future buildings. Futuristic buildings coexist with the legacy of the past and harmoniously fit into the style of the area. And the plasticity of their facades reflects the dynamism of modern cities. These projects differ from traditional buildings not only in their architectural appearance but also in their rich infrastructure. In addition, they often embody the most daring and progressive ideas of their time. We are constantly in contact with building materials. Metal handles, wooden walls, and glass windows would create a completely different atmosphere if the handles were, say, glass, the walls were metal, and the windows were wooden.

And yet, before embarking on a detailed design of the future building, it makes sense to determine its style at least approximately. If it will be a fusion-style building (some experts consider the term "eclectic" already obsolete), then such a decision should not be spontaneous, but meaningful and justified. It is worth understanding what elements of which styles the country house will combine, whether one

**Figure 1.** *The modern architecture between form and functions.*

component will dominate the others, how harmony can be achieved in the resulting exterior, and so on. Separately, you need to think about the materials and technologies that will be used in the construction process: how to emphasize the creative idea with their help and facilitate its implementation, what new and unexpected esthetic solutions the material or technology itself can offer the architect (**Figure 1**). The material is as important to the building as its form, function, and location.

In the circular bio-economies which will gradually entrench themselves in many parts of the world, wood, as a renewable material of construction, will reign again as a dominant material in anthroposphere structures, supplanting the now-prevalent nonrenewable materials. Wood wastes generated in the forestry sector will lend themselves to being reworked and recycled back into the anthroposphere [1, 2]. It is not just the fact that it is renewable and abundant which makes wood a favorite in the architecture, building, and construction (ABC) sector of a circular bioeconomy. It is strong and light, has good thermal insulation properties [3], has the ability to resist shock loads without getting damaged, and dampens vibrations (thus resisting seismic shocks). It is highly malleable and workable and lends itself well to gluing, being joined by fasteners, etc. In Europe, wood found used in the past as the main building material for temples, towers owned by appanage princes, and peasants' farmsteads and is more common within Europe, in Scandinavia. Many Finnish, Norwegian, and Swedish citizens expressed different views on the acceptability of the use of wood than their fellow-Europeans in Austria, Denmark, Germany, and the United Kingdom [4].

Expanding the scope of use of wood and finding creative and innovative ways of incorporating wood waste back into the anthroposphere supports the paradigms of circular bio-economies [5]. If the processing turns out to be complex, the wood itself can be modified and conferred with improved properties. Modified wood is a new material in which its anatomical structure is preserved, while its physical and mechanical properties are significantly improved. Various types of modified wood are used not only as substitutes but also as full-fledged, promising composite materials. The static flexural strength of Wood-Based Laminate Constructions comes in handy

as they frequently experience static flexural and compressive deformation during service [6].

The mechanical properties of wood depend on a host of factors, the most important of which are the nature of the load, the direction in which it acts on the fibers, the speed and the duration of the load, as well as the structural defects in the wood, effects of humidity, etc. The mechanical and deformation characteristics are determined in the laboratory on small specimens made of defect-free wood, thus obtaining the standard strengths of the ideal wood under short loads. The modulus of rupture (MOR) and modulus of elasticity (MOE) are determined using nondestructive (NDT), semi-destructive (SDT), and destructive (DT) test methods [7]. The moisture content is also determined, as it must be remembered that variations in moisture content cause local swelling or shrinkage, thereby changing the distribution of stresses and impacting the strength and bearing capacity adversely [8]. Variation in the quality of wood is common, both within the same species and across different species; and the sources of such variations are diverse. It is found that most of the mechanical properties of the glued wood elements are superior to those of the wood in the component elements. This may be reasoned out as follows:


### **2. ABC<sup>1</sup> and wood**

Wood, it goes without saying, is one of the oldest building materials. Houses, towers, and bridges of yore were built with wood. Special wooden structures circles—were used in the construction of ancient arches [10]. Centuries of experience and scientific research have shown that during normal operation of wooden structures, their service life is measured in centuries. An example of this is the oldest wooden bridge in Europe—the Chapel Bridge in Lucerne, dating back to 1330. The use of wood and its derivatives in construction and especially for insulation and finishing depends to a large extent on its favorable thermal properties. By virtue of its low coefficient of thermal conductivity vis-à-vis other materials of construction, even a light/thin wood frame wall may provide a structure with adequate mechanical properties and an acceptable level of thermal insulation [11]. The interest in "zero-energy" or "low-energy," or "climate-positive" constructions with a reduced demand for externally supplied heat energy has entrenched itself in academic, research, and ABC circles and is sure to be fueled into the future [12]. Talking of thermal conductivity,

<sup>1</sup> ABC stands for Architecture, Building and Construction … . used here as a pun to make the sub-heading attractive.

the coefficient λ of dry wood (at a moisture content below 20%), ranges between 0.14 and 0.21 W/m.K. It is noteworthy that thermal conductivity in a direction perpendicular to the fibers is lower than in a direction parallel to them (which is quite intuitive). It is dependent on the density and the moisture content of the wood. For densities in the range of 300–800 kg / m<sup>3</sup> , and moisture content lower than 40%, when heat flows perpendicular to the fibers, the thermal conductivity coefficient can be calculated as shown in Eq. (1):

$$
\lambda\_0 = [237 + 0.02\rho\_0(1 + 2\rho)]10^{-4} \tag{1}
$$

where


Experimental tests have shown that in the temperature range from 20–100°C, the thermal conductivity coefficient can be determined by the relation shown in Eq. (2):

$$\lambda = \lambda\_0 \left[ \mathbf{1} + (\mathbf{1}.\mathbf{1} - \mathbf{1}0^{-4} \rho)(\Theta\_w - \mathbf{20})/\mathbf{100} \right] \tag{2}$$

where


Among other things, sustainable construction is a strategy adopted these days to move steadily, surely, and slowly toward the goal of net-zero greenhouse gas emissions. Focusing merely on the use-phase and urging consumers to reduce their energy usage is necessary but not sufficient. It is here that a material like wood, adopted in the design stage itself, complements the efforts which the inhabitants of buildings would also make [13].

Like all materials in general, wood expands and contracts in response to temperature variations. This variation, which is expressed in terms of the coefficient of thermal expansion αT is not essentially the same along the three axes—longitudinal, tangential, and radial. Its value in the longitudinal direction (parallel to the fibers) lies between 3E6 and 6E6, while it is much higher in the tangential and radial directions perpendicular to the fibers—between 10E6 and 15E6. If one compares the coefficient of longitudinal thermal expansion of wood with those of steel and concrete (materials which wood can replace in structures), then wood is much lower. This implies that thermal expansion joints are not required for wooden constructions. This is also bolstered by the fact that temperature changes lead to variations in moisture content (water evaporating when it gets warmer, for instance), leading to contractions (or swelling) in directions opposite to the thermally induced deformations [2]. The

specific heat (c) for wood (moisture content below 20%) is about 5.07 W/kg.K. It must be noted that the specific heat is quite sensitive to the moisture content of the wood:

$$c = \mathbf{1}.\mathbf{16}(0.324 + \boldsymbol{\mu})/(\mathbf{1} + \boldsymbol{\mu})[\boldsymbol{w}/\log \boldsymbol{\star}\boldsymbol{K}]\tag{3}$$

Part 1.2 of the EUROCOD 5 standard proposes the calculation of specific heats, for a humidity ω and a wet bulb potential temperature, Θ*w*with the relation [14]:

$$\mathcal{L} = \left(\mathfrak{c}\_{\theta} + o\_{cap}\right) / \left((1+o)for\Theta\_w \le 1000\,\mathrm{^\circ C}\right.\tag{4}$$

$$
\sigma = \sigma\_{\theta} \text{ for } \Theta\_w > 1000^\circ \text{C} \tag{5}
$$

where.

c<sup>Ɵ</sup> = 1110 + 4.2 Θ <sup>w</sup> (specific heat as a function of temperature). cwater = 4200 J / kg K (specific heat of water).

#### **2.1 Quality of wood**

The market imposes several quality requirements on products made of wood. Every sector which finds use for wood has its own range of specifications when it comes to wood species and quality [15]. Wood demanded by the construction sector, thereby, is categorized into different quality classes, and the prices are proportional to the quality [16]. In the current international calculation standards for building structural elements, quality classes are associated with predefined values of mechanical strength at different stresses, or physical characteristics:


The behavior of wooden structures over time needs to be monitored. Wooden structures are used in building coverings, agricultural construction, and rooms where there is a likelihood of exposure to aggressive chemicals [20]. Wooden structures are also widely used by landscape architects in the construction of pavilions, gazebos, bridges in parks, gardens, and other natural ensembles. In construction, coniferous wood is most often used [21, 22]. Elements of wooden structures are connected to each other by means of glue (glued structures) or with the help of nails, dowels, and other fasteners. The most widespread are glued structures—this technology allows you to create strong and durable elements of almost any shape and size.

### **3. SWOT2 for skyscrapers in modern cities**

Skyscrapers, being tall, inevitably become an important part of the cityscape. The world's most iconic skyscrapers have silhouettes which people instantly recognize, like the peak of a popular mountain or the familiar face of a friend. It is unlike a sculpture or painting; in that it cannot be the work of a single artist. It is a product of teamwork, resulting from numerous collaborative exercises among architects and CEOs, steelworkers and engineers, bankers, and billionaires [23]. Architects mull over what a freestanding skyscraper would look like and how it would look alongside, behind, or in front of the surrounding buildings. All buildings together constitute the skyline of a city. Quite like the different buildings that make them up, the skylines of different cities are also different from each other, in general. Skyscrapers can be considered as reflections of the culture and values of the inhabitants of the city they belong to, and on account of their massiveness and by the tower over all other structures in their vicinity, they end up attracting attention invariably, and defining the city or becoming almost synonymous with it [24, 25]. The Makkah Royal Clock Tower in Mecca (Saudi Arabia), for instance, has a large clock which shows time—an important factor for Muslims—and is easily visible to the people of the city. Taipei 101, in Taipei (Taiwan), was designed in eight sections because "8"is a lucky number in China—the Chinese word for this number is homophonic with the word for prosperity. High-rise buildings must not only be viewed from an urban planning and architectural perspective, as the sociological perspective provides useful insights into the history of urban development. Towers, skyscrapers, and high-rises have been added to the cityscapes of the world over the last 100 years, to facilitate efficient land use and in response to the rising rate of urbanization worldwide. The earlier design approaches of high-rises were sheathed in the traditional fake clothing of postmodernity. However, the development of modern architecture was more inclined to modular repetitions and broad abstractions integrated into the international style [26]. The typical American highrise construction developed from the 1880s onward, beginning in Chicago and New York. Chicago was, at that time, an important industrial and commercial city, next only to New York. Sustainable skyscrapers, while making economical use of available land, facilitate energy-saving and provide comfortable habitation for the urban denizens.

Veritably, they are the icons of modern cities. They inspire man to aspire for greater goals and keep aiming higher (readers may wish to read Ayn Rand's The Fountainhead to understand the "spirit of the skyscraper," so to say) [27]. The timid out-of-towner can suitably palpitate on entering the bright lobby, while Superman or Superwoman can aspire to the executive floor or even higher! [28]. Although people have mixed reviews of skyscrapers, it is undeniable that skyscrapers have played an important role in strengthening the vertical development of cities, preventing excessive horizontal expansion, multiplying the capacity of a city's population, and shortening the distances people travel. It can be reiterated here that they have dominated the cityscapes ever since they came into being, visible to one and all, from both near and far [29]. However, if the race of skyscrapers were even a thousand times a vanity fair, their construction would not cease to be the most difficult engineering problem. There are parallel directions of development in the world. It starts with the development of large territories, including industrial zones, dilapidated

<sup>2</sup> Strengths, weaknesses, opportunities, and threats.

housing stock, and places that are now turned off from the city's work. In such cases, the urban planning task becomes primary—creating the right balance of the territory, an effective street-and-road network, transport accessibility, social infrastructure, and parks. Here, of course, there is really no desire for high-density development. The main goal is to include the place in the city's "work" and activate it by creating jobs and infrastructure [30].

#### **3.1 New code in an UN-sustainable building standard**

The rapid urbanization of the planet and the imminent challenges of climate change compel us to reconsider the purpose and form of development of cities. Last year, the participants of the Third International Conference on Housing and Sustainable Development, organized by the UN-Habitat Center, adopted a new urbanization plan. Sustainable urban development means that we must make them comfortable not only for ourselves but also for future generations—including protecting them from the adverse impacts of climate change [31]. Yet, at the same time, cities themselves "contribute" to global warming by being the fount of greenhouse gas emissions.

In order to control the contribution of cities to global warming, energy efficiency is the watchword. New building construction should occur by new norms and standards that ensure energy efficiency, while ensuring comfort for residents, with a salubrious indoor climate [32]. City administrations must prioritize investments in public transportation, while residents themselves must take initiatives to drive less and walk or use their bicycles more. Greening the city is of paramount importance, with the setting-up of parks, planting trees adjacent to sidewalks, and preserving any sylvan surroundings which may exist near the cities as these are carbon-sinks—veritably, the lungs of the city. Development must be harmonious, without anything "good" being overly compromised to augment another. The focus must be on the resident, not on accommodating more and more people in the city come what may, and not certainly on increasing the profit margins of the builders.

#### **3.2 Examples of sustainable wooden skyscrapers**

Wooden structures remind one, at first thought of small, idyllic cottages in the "middle of nowhere" (in the "woods," so to say), but wood will soon become the material of choice, as mentioned earlier for more and more structures in urban settings too. As referred to earlier in the chapter, wooden buildings in cities have been around in Scandinavia for quite some time, with Norway boasting of perhaps the tallest wooden building on date [33]. The penchant for including more and more wood in the housing stock of cities has now spread to other countries in Europe, Asia, and the USA. Of course, when one talks of skyscrapers built with wood, it must be remembered that it is always along with other materials like concrete. This ensures that some necessary properties like fire resistance and vibration damping are not unduly compromised. Concrete though is not environmentally friendly and is associated with high greenhouse gas emissions, with carbon dioxide being emitted not just owing to combustion of fossil fuels upstream but also released from the calcium carbonate which is the principal raw material for cement [34]. Researchers have been seeking solutions to tide over this issue, and there should be some on the horizon soon.

A solid wooden beam is covered with a thick, solid, white layer on top. Dry wood is not damaged by exposure to corrosive gases and chemicals, and in that regard, scores over metals and concrete. One however has to reckon with hygroscopicity, structure

heterogeneity, and inflammability. The last-named property has been responsible for the destruction of several wooden structures constructed in the past.

#### *3.2.1 Skellefteå cultural center: Sweden: 2019*

The Swedish city of Skelleftea inaugurated a 20-story "skyscraper" built entirely of wood and other sustainable materials in September this year, the publication said. Construction has an important role to play: to provide environmentally sustainable alternatives. Skelleftea is a community of 30,000 people, just 200 kilometers south of the Arctic Circle. As the forestry sector is very well developed in this part of the world, the authorities resorted to wood. It is, in a way, as far as Scandinavia is concerned, as mentioned earlier, a kind of a déjà vu, a return to the past [35].

The 75-meter-high building is a cultural center that houses 6 theaters, several art exhibitions, a library, and a hotel with over 200 rooms (**Figure 2**). Above all, however, the role of the building is to abate pollution in the area. "The original idea was not a simple 20-story house in Skelleftea, but a strategy that meant that Skelleftea not only survived, but also developed." The building is built with the help of over 12,000 cubic meters of timber, extracted from the immediate vicinity of the town, thus reducing transportation costs and, implicitly, pollution [36]. The cultural center is based on laminated wood pillars, thus completely avoiding the use of cement. The cement industry is responsible for about 7 percent of global carbon emissions, according to the International Energy Agency (as also mentioned earlier, carbon dioxide is emitted from calcium carbonate, in addition to from the fossil fuels which may be used as heat energy sources). The building is equipped with solar panels, storage batteries, and solar-powered heating systems. Even the building's fire sprinkler system, which usually runs on fossil fuel elsewhere, is powered by renewable

**Figure 2.** *The design of the Skellefteå cultural center.*

*Sustainable Wooden Skyscrapers for the Future Cities DOI: http://dx.doi.org/10.5772/intechopen.105809*

energy. The remaining energy, stored in the batteries, is then supplied to other usage points in the city, making the skyscraper a so-called prosumer.

#### *3.2.2 Trätoppen "tree top" Stockholm: Sweden: Proposed*

This is a 40-story, 133-meter-tall, 35-meter wide, and 18-meter-deep wooden skyscraper with 850-square-meter apartments per floor, which could well become the tallest building in the Swedish capital city. The facades' original "digital" decor is inspired by the numbers in the old car park, showing which floor the driver is on Treetop, which translates as "top of the tree." This 40-story building will stand out surely as one of the many icons in Stockholm and will surely attract tourists who come to the city (**Figure 3**). It will be 25% lighter in mass than a similar skyscraper built with reinforced concrete and will necessitate a smaller and "shallower" foundation [37]. There, however, are challenges related to lack of durability which have to be overcome [38]. In recent years, significant advances have been made in wood-based composite materials, such as cross-laminated wood (CLT panel), consisting of crosslocated sawn softwood and hardwood with fibers glued at a certain angle. And just as carbon fiber composites are used to make race cars, planes, and golf clubs stronger, CLT adds durability to wood structures.

#### *3.2.3 Mjøsa tower: Norway: 2019*

The 18-story Mjøsa Tower or Mjøstårnet (the tower of Lake Mjøsa) in Brumunddal, Norway, which is 85.4 meters tall. The base cross section of the building is a 37.5 x 17 meters rectangle and approximately 11,300 m<sup>2</sup> . Adjacent to it is a 4700 m<sup>2</sup> swimming pool, also with a wooden structure (**Figure 4**). The supporting structure is made entirely of glulam beams and pillars, while the balconies, stairwell, and elevator are made of X-Lam structural wood panels. To maximize the project's environmental sustainability, the wood used was obtained from local forests and two new

**Figure 3.** *The "Trätoppen" tower in Stockholm—Sweden (proposed project).*

trees were planted for each one cut down, reflecting the high Scandinavian standards of management in the forestry sector. Fire safety is taken care of, in this skyscraper [39]. Untreated solid wood creates its own fire-resistant surface as the outer layer chars in a fire, making the wood immune to further fire-induced damage. Fire safety regulations state that a building must withstand a full fire for at least 2 hours without collapsing. The floors of the first 11 floors are made of wood, while the floors of the last 7 floors of the tower are reinforced with concrete. Now, higher one is in a building, be the building made of concrete or wood, it sways. In the case of the Mjøsa Tower, the weight of the concrete on the upper floors dampens the tendency to sway, restricting it in the topmost floor to about 14 centimeters.

The facility includes home offices, a hotel, and apartments. The construction project is a testament to how more massive and less environmentally friendly concrete can be replaced with wood. This high-rise Mjøsa Tower was built from glued laminated timber, cross-laminated timber, and Kerto LVL [40]. To achieve the required load-bearing capacity, cross-glued Kerto-Q laminated veneer lumber panels are also used as the material for the floors. The plates are characterized by their robustness and resilience. The construction time thereby has decreased by 35–40% vis-à-vis working with cast-in-place concrete, thanks to the lightness of wood [41].

#### *3.2.4 Multi-story wooden building "Treet" (Bergen, Norway): 2015*

The building was recently built in the Norwegian city of Bergen**—**a 14-story, 52.8 meter-tall, 62-apartment high-rise residential building called *Treet* (which translates as "Tree"). The previous tallest wooden building was the 32-meter-tall Forte building in Melbourne, Australia. The load-bearing structures of the building are mainly made of glued laminated timber, a building material made by longitudinally gluing wooden boards (lamellas) with waterproof glue. Concrete was only used for the three main floors, which served as platforms for four tiers of stacked modular sections [42].

*Treet*, located near the Paddleford Bridge, is constructed as a wooden building with glulam beams as the outer and inner skeletons and has 14 floors above the plinth in

*Sustainable Wooden Skyscrapers for the Future Cities DOI: http://dx.doi.org/10.5772/intechopen.105809*

**Figure 5.** *The conceptual and execution phases of a "Treet" building.*

concrete which includes parking spaces and the main technical installations. The 5th and the 10th floors of the building are more securely attached to the glulam beam skeletal structure, to dampen swaying when it is windy (**Figure 5**). The other floors consist of prefabricated modules. The main difficulty was to find a place for all the engineering systems. About 180 mm of space was allocated under the ceiling, in which it was necessary to fit the sprinklers and ventilation and lighting systems [42]. Therefore, when prefabricating the modules, the margin for error was very small. A special glued beam capable of withstanding fire for 90 minutes was used, without compromising the structural integrity in any way. Refractory paint was used for finishing work. In addition, the building was designed in accordance with stringent standards governing energy consumption in passive houses, which necessitated extra attention to be given to heat recovery in HVAC systems and associated piping. Separate sprinkler placement drawings were required, as they had to be installed in the balconies.

#### *3.2.5 HoHo tower: Vienna: 2018*

The new 84-meter high 24-story HoHo tower in Vienna, Austria, which will be the tallest wooden building in the world, has been underway for over a year. Approximately 76% of the structure will be wooden [43].

Vienna is a city with numerous baroque buildings and architecture from the era of Grinders.

The HoHo skyscraper will house apartments and offices, spa and wellness centers, restaurants, and one hotel (**Figure 6**). Constructing such a tall structure in wood requires meticulous planning, a team of creative designers, architects and engineers,

**Figure 6.** *The HoHo tower in Vienna.*

and appropriate building infrastructure This tower in Vienna is an exemplar of ecofriendliness and economy [43].

In HoHo, massive cross-laminated wood elements and prefabricated concrete panels are combined. A deliberately "simple" system uses the laying of four prefabricated serial building elements: supports, ceilings, and facade elements. The novel woodconcrete composite ceiling elements reduce the proportion of steel fasteners in the construction. Prefabrication of wooden structures takes place under controlled conditions. The supports, in turn, form a single mounting element with similar prefabricated solid wood exterior wall modules. This modular design approach [44] decreases the working time on the construction site. It facilitates the avoidance of problems associated with adverse weather conditions and long drying periods. However, one needs to bear in mind that the visible wooden surfaces need to be handled carefully, as they would form the inner envelope for the houses and are meant to contribute to a feeling of coziness and not detract therefrom. The way space is engineered within the building is flexible and can be changed any time, without incurring high costs and extra effort. This contributes directly to the durability of the building.

#### *3.2.6 W350 project: Japan: proposed*

This project is a proposed wooden skyscraper in downtown Tokyo (Japan), which was announced in 2018. The Timber Interface consists of wood with a small cross section; thus, it can be used for renewing installations with a short lifespan, daily cleaning of windows, and general maintenance of buildings (**Figure 7**). About 70% of Japan's land is forested, and 40% of the forested area, i.e., approximately 30% of the land, is artificially forested. The well-managed practice of tree planting, logging, building production, and replanting has favored the national environment of Japan's lands, climate, cities, and forests, maintaining forestry and the surrounding area [45].

The "W350 Plan" is an R&D concept that aims to further advance this technology and realize an "environmental wooded city with the goal of reducing the total greenhouse gas emissions of "embodied carbon" during the construction phase of the life cycle, to curb climate change [46]. Many companies work to develop refractory materials and genome selection breeding to realize a highly durable and comfortable building space using wood. The skyscraper will be 90% wood, the rest being steel which will serve the purpose of providing the skyscraper with wind and seismic

*Sustainable Wooden Skyscrapers for the Future Cities DOI: http://dx.doi.org/10.5772/intechopen.105809*

#### **Figure 7.** *The futurist tower "W350 project" in Japan.*

resistance. Wood too, for that matter, is known to be resistant to seismic shocks. The project requires 185,000 cubic meters of timber and plans to revitalize forestry and timber demand in Japan [47]. In addition to esthetics, the choice of wood is intended to "turn the city into a forest." Wooden structures are also easier—when compared to concrete structures**—**to repair or replace if they collapse. It is estimated that the costs for fashioning wooden structures and incorporating them in buildings will continue to decrease due to technological advancement.

Eight years ago, a law was passed in Japan that requires construction companies to use wood in public institutions smaller than three stories [48]. There are other such constructions globally, although not as tall as the one proposed for construction in Japan. There is an 18-story wooden office building in Minneapolis and a 16-meter-tall student apartment building in Vancouver. Sumitomo Forestry, which develops businesses that utilize wood such as housing and building materials, has said that it looks forward to utilizing a lot of wood in the building and construction sector over time, in Japan.

#### *3.2.7 The Chicago River beech tower—A vision of new building*

It is a collaborative research effort aimed at identifying challenges and opportunities for the design of increasingly high-mass timber structures. The Chicago River Beech Tower is an 80-story, 300-duplex-unit residential building, which just about stays within the upper range established for residential towers in the city [49] (**Figure 8**). While the River Beech Tower structure is well balanced, an increase in material volume was expected as the design progressed.

The River Beech Tower aims to provide the understanding necessary to design and build large buildings using next-gen engineered wood structures.

#### **4. Results and conclusions**

Climate change has been a key driver in the resurgence of wooden structures in building and construction in urban settings. Wood is a solid material made up of

**Figure 8.** *The Chicago River beech tower.*

organic substances (cellulose, lignin, etc.) with carbon, hydrogen, and oxygen as the main constituent elements. From a microstructural point of view, it is made up of supporting and guiding tissues. The structure of the wood can be comprehensively studied by observing its cross section, the radial longitudinal section, and the tangential longitudinal section.

Wood has rarely been used in the construction of high-rises, but that is about to change, as the examples described in the chapter illustrate. Though it is inflammable and many old wooden buildings have been gutted down by fire, wood is essentially a carbon-sink (which stores up the carbon in it during its use phase as a building material for a long time), is hard and light, is easily workable, has very good acoustic and thermal properties, reduces the size and the cost of the foundations of a building, and provides occupants with a more comfortable and healthier indoor environment.

The wooden skyscrapers described, and those which may likely spring up in the years to come, in other cities of the world include many architectural functions such as offices, hotels, shops and residential units, garden roofs, terraces covered with greenery, water features, and huge interior spaces filled with natural light. The revolutionary construction is made of a durable material called glulam, which is made up of wooden planks that are glued together to form beams.

The use of wood essentially comes as a response to the need to rethink our approach to buildings in cities and pursuing the paradigm of zero-emission and energy-neutral buildings, toward the achievement of Sustainable Development Goal # 11—sustainable cities and communities. Indeed, they are not panaceas to all the challenges which humankind dwelling in cities faces on date, but surely, one step forward in the mitigation of and adaptation to the adverse effects of climate change.

Even if ultrahigh buildings are erected today for a different purpose—to display wealth, power, grandeur, and ambition, it would be wise to do that in a sustainable manner—and earn bonus points in the process!.

*Sustainable Wooden Skyscrapers for the Future Cities DOI: http://dx.doi.org/10.5772/intechopen.105809*

#### **Author details**

Amjad Almusaed<sup>1</sup> \* and Asaad Almssad<sup>2</sup>

1 Department of Construction Engineering and Lighting Science, Jonkoping University, Sweden

2 Faculty of Health, Science and Technology, Karlstad University, Sweden

\*Address all correspondence to: amjad.al-musaed@ju.se

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## Section 2
