Timber Skyscrapers: A Low-Carbon Typology for the 21st Century
Wood, an age-old building material, has left its mark on the history of architecture. Structures like townhouses and ancient cathedrals have seen usage and innovation with wood as a primary material. As technology evolves and urban landscapes grow skyward, wood has emerged as a strong contender to steel and concrete in the area of skyscraper design. Recent advances in engineering, materials science, and construction techniques have welcomed a new era of experimentation, enabling the construction of timber skyscrapers across the world. Timber skyscrapers signify a departure from traditional construction methods, seamlessly blending aesthetics, functionality, and ecological consciousness. Wood as a material, with its inherent strength and impressive fire resistance, presents hope to an industry in pursuit of a more sustainable future.
In the 21st century, climate change has escalated into a pressing concern. The construction industry consumes about 40% of the world’s energy and is responsible for almost one-third of greenhouse gas emissions. Conventional materials that evolved in the industrial era, like concrete and steel, stand as culprits for the industry’s large demands. The production of cement alone accounts for a large proportion of energy needs in construction. A much needed transformation in the architecture and construction industry has motivated architects and engineers to ideate alternatives that prioritize both environmental responsibility and aesthetics.
Timber, a material with inherent green properties, is being increasingly used in construction projects worldwide. In contrast to concrete, which undergoes manufacturing processes notorious for their carbon emissions, trees function as natural carbon absorbers throughout their lifespan. When these trees are used to create engineered wood, they continue to sequester carbon rather than release it into the atmosphere when they die. Studies show that a single cubic meter of wood can store over a ton of carbon dioxide, positioning timber as a promising material for achieving carbon negativity in construction. The production of engineered wood demands less energy than concrete and steel. Furthermore, it is a renewable resource and can satisfy a resource-intensive construction industry.
As a building material, timber possesses a myriad of qualities that render it an excellent choice for constructing skyscrapers. Its lightweight property not only reduces the load on the foundation but also facilitates efficient transportation and on-site assembly. The material’s flexibility aids its structural resilience, especially in regions prone to seismic activity. Cross-laminated timber, a form of engineered wood, offers impressive strength and rigidity, bolstering a building’s capacity to withstand earthquakes. Buildings made of engineered wood are quicker to construct and structurally stronger, and have been rising in popularity in recent years.
In today’s construction landscape, various forms of engineered wood are available in the market. Engineered wood, also known as “mass timber” or “structural timber,” is crafted by bonding together individual pieces of softwood to create larger, reinforced components, thereby enhancing its structural integrity. Glulam, short for glued laminated timber, and cross-laminated timber are both recent advancements in wood engineering. Engineering wood to augment its strength and versatility is not a recent concept – plywood has been a popular building material since the early twentieth century. The resurgence in engineered wood construction with regards to skyscrapers has led to the coining of the term “plyscrapers”, marking a shift in architectural design and sustainability.
The need to address climate change has sparked a demand for sustainable resources, enabling advancements in wood construction technology. Simultaneously, public perception regarding wood as a material for high-rise structures has been steadily evolving, leading to a growing list of wood skyscrapers constructed in the past decade:
Rising to a height of 280 feet, Mjøstårnet is a remarkable architectural feat encompassing 18 floors of mixed-use programs, located in Brumunddal, Norway. The structure comprises office spaces, residential units, and a 72-room hotel, and has become a sought-after destination for those intrigued by the future of sustainable architecture. In a country where buildings rarely exceed ten stories, Mjøstårnet serves as both an audacious gesture and a proof of concept for wood high-rises. Its strength and stability, however, defy convention, replacing steel and concrete in favor of colossal wooden beams made of glulam. This engineered marvel binds pieces of lumber together with water-resistant adhesives, illustrating the potential of timber in revolutionizing modern architecture.
Austria-based Studio Precht has introduced an innovative timber skyscraper concept called “The Farmhouse,” that marries modular housing with vertical farming. At its core, the design features prefabricated A-frame housing modules constructed from cross-laminated timber (CLT). This conceptual modular system employs a three-layered approach for each module’s walls – the interior layer holds the electrical and plumbing infrastructure along with surface finishes. The outer layer accommodates gardening elements and a water supply while the layer in between provides structural support and insulation. The system exhibits adaptability in terms of tower height, as it can adjust to varying structural thicknesses, allowing it to iterate based on national building regulations across the world. Some countries like Japan, Canada, Scandinavia, Austria, and the UK have embraced CLT for constructing buildings ranging from 18 to 30 stories, with global building codes increasingly adapting to this timber innovation.
HoHo Vienna stands as a towering testament to high-rise timber construction, currently ranking among the world’s tallest buildings with a height of 275 feet. The project is situated on one of Europe’s largest urban development sites and is designed to contain a diverse array of amenities, including a hotel, apartments, restaurant, wellness center, and offices. To support the height of the structure, conventional glulam’s load-bearing capacity would have been surpassed due to the limitations of raw timber width. Instead, “block-glued” components were developed using specialized press technology, meeting the increased structural demands of the building. The project required a substantial 365 m³ of glulam and 1,600 m³ of cross-laminated timber (CLT), all of which were produced, prefabricated, and efficiently delivered to the site. The majority of building components were prefabricated, streamlining the construction process, reducing on-site procedures, and saving time. Each prefabricated element received a protective moisture barrier to withstand on-site weathering. The HoHo Vienna system, designed for simplicity, stacks four prefabricated building elements – supports, joists, ceiling panels, and façade elements. With the lower structure completed, the installation of the initial prefabricated wooden elements is underway.
Building towering wood structures for global cities promises a sustainable and innovative future, however it also presents a set of challenges. Engineered wood is still in its infancy and can often be more expensive in comparison to conventional construction materials. The construction of Mjøstårnet cost approximately $113 million, about 11% higher than the cost of a similar development in concrete and steel. The availability of timber resources also influences preference towards the material. Regions like Germany, Austria, and Canada have abundant, harvestable forests, while others lack a readily accessible wood supply for engineered timber. Consequently, countries without a tradition of using wood in construction may not readily engage in architectural innovation with this material. Timber’s structural elements also tend to be larger than their steel or concrete counterparts, intensifying resource consumption and reducing rentable space — a concern for real estate stakeholders. Fire safety remains an issue for tall timber structures, prompting ongoing research into fire-resistant coatings and techniques to enhance the materials performance.
Around the world, numerous proposals are emerging to revolutionize urban architecture through the construction of wood skyscrapers. In Tokyo, Japan, the ambitious W350 Project is setting its sights on a towering height of 1,150 feet, with aspirations for completion by 2041. What makes this project particularly groundbreaking is its commitment to sustainability, intending to utilize a mere 10% steel and predominantly engineered wood in its construction. Meanwhile, London is embarking on its own timber journey with the Oakwood Tower, projected to reach a height of 980 feet, while Chicago explores the concept of the River Beech Tower, reaching a height of 748 feet. These endeavors underline the promising potential of wooden skyscrapers, driven by continuous technological advancements and global prototyping efforts. As these proposals evolve into reality, it is truly awe-inspiring to witness the boundless innovation and experimentation shaping the future of sustainable urban architecture.
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