1 – Tall buildings
Chicago and New York invented the skyscraper not only because they had clever minds and technology, but also because of their extremely competitive commercial context. Skyscrapers started to rely on load bearing structures in masonry. Later, towers as the Empire State Building, with a steel structure enclosed with masonry elements, became the standard. After the Second World War, lighter steel structures, with a central core and an exterior glass curtain wall, dominated the scene. At this stage the archetype of the skyscraper was the Mies van der Rohe steel and glass tower.
After decades of repetitions and variations of the international modernist skyscraper, some architects and engineers are now busy designing weird forms, while others are trying to break the record of the taller tower.
Recently and against the stream we heard about new directions: architects, engineers, builders and owners are talking about “tall wood” buildings.
2 - Wood towers technology
Some 10 years ago mentioning wooden skyscrapers would be regarded as a sign of insanity. Now it is considered as a mark of innovation, entrepreneurship, and environmental awareness.
Besides some nice historic examples such as the Japanese temples, or the “fachwerk” buildings of central Europe, contemporary tall wood buildings can be linked to the tradition of XIX century timber frame building of North American cities. They were designed with a very interesting and logical type of construction: an interior heavy timber post and beam structure protected by fire resistant external walls in brick. Usually these were intended to be warehouses or commercial buildings, with up to nine storeys. A beautiful example of these is the 9-storey Butler Square building in Minneapolis. As it is mentioned in Detail magazine 1/2.2018, the innovation of this building technology was stopped by fire codes in Canada and in the USA restricting the number of storeys, to seven first and to four later.
The advances in wood construction technology, especially with Glulam and Cross Laminated Timber, combined with the sustainability trend put wood again in the main stage. The introduction of sprinklers and the use of protective claddings, intumescent paintings, or the over-dimensioning of wood components drove codes to a change, allowing buildings with those wooden structures to reach higher heights.
Wood started also to be understood as a friendly material. Building with wood structures instead of steel and concrete can optimize carbon sequestration. The argument is that the absorption of CO2 by trees varies with age. Young trees grow rapidly, so they absorb more CO2 than mature trees with a decelerating rate of growth. As mentioned by Michael Green and Jim Taggart in “Tall Wood Buildings”, when trees start the decaying process they emit more CO2 and forests without regeneration can become CO2 emitters. This means that “By optimizing the volume of wood harvested from our forests (…), we can also optimize carbon sequestration”. The magic number of carbon storage is roughly 1 ton per cubic meter of wood.
The other factor in favour of wood is the embodied energy… but when presenting this argument, some people say that countries without local sources of qualified wood, like Portugal, would require a lot of energy in transportation to get the necessary wooden structural components. Nevertheless, calculations made for the United Kingdom concluded that cross laminated timber panels from Germany and Austria, transported by road, have a lower carbon footprint than local produced concrete.
3 – Tall wood authors
Perkins and Wills, Michael Green, Acton Ostry Architects, Shigeru Ban, and Waugh Thistleton are some of the authors involved in new tall wood buildings. Michael Green has been one of the most active architects on the promotion of this new type of construction. He was responsible for a research report called “Tall wood” (2012) focusing on the feasibility of buildings up to 20 storeys made by Glulam and CLT panels. Following that he proposed a 30 storey building for Vancouver and the Baobab (hotel/ residential) for Paris, with 35 storeys.
Maybe one of the pioneers of tall wood was the Murray Grove Stadthaus building, finished in 2008. With nine storeys (8 in wood plus 1 in concrete), it was designed by architects Waugh Thistleton and engineers Techniker. Hackney borough in London, where it is located become a centre of wood innovation, presenting now, at least, 23 buildings with Cross Laminated Timber.
After that, a significant amount of buildings, as the Forte in Melbourne Australia, by Lend Lease, reached the 10 storeys plateau. In 2015 the 14 storey Treet Building, by Artec Architecture, was completed in Bergen, and in 2017 the hybrid Brock Commons Student Residence, by Acton Ostry Architects, was finished in Vancouver, with 18 storeys. The HoHo by Rudiger Leiner Architekten in Viena, Austria, with 24 storeys, to be completed in 2018, could be the next record.
Many other proposals are being designed. Here are some of them: White Arkitekter with a competition proposal for Sida Vid Sida, a Hotel and cultural centre for Skelleftetea with 19 storeys, Tham & Vidergard planned four 20 storey apartment buildings for Stockholm, Team V Architectuur with Lingotto, Nicole Maarsen and ARUP are designing the Haut in Amsterdam with 21 storeys, RPL Rudiger Laine + Partner are working on a 24 storey building for Vienna, C.F. Møller's proposed a design for the HSB Stockholm's architectural competition 2023 with 34-storey. Finally Sumitomo Forestry, a Japanese timber company is working on the world's tallest wooden building to be built in Tokyo. It is expected to be a 350-metre, 70-storey hybrid timber skyscraper, built to mark the company's 350th anniversary in 2041. The designers are Sumitomo's Tsukuba Research Laboratory in collaboration with Tokyo office Nikken Sekkei.
The Barbican Oak project for the city of London is an ongoing research exploring a design of up to 80 storey timber. The designers are PLP Architecture with the Centre for natural Material Innovation at Cambridge University and engineers Smith and Wallwork. This team is exploring the potential benefits of timber structures other than the ecology of the material: lower costs, reduced construction times, fire resistance and light weight. The Barbican Oak Project stated that while a building in concrete has 300Kg/m3 and a steel buildings has 160Kg/m3, a building such as the Timber Tower would have only 70Kg/m3. This implies some challenges like the ones related with uplift, wind and seismic forces, but it implies also important material and foundation savings.
4 – Tall wood Design
Basically we have three types of tall wood structures: the panels, the post and beam and the mixed. Panels are usually associated with residential projects where load bearing walls are coincident with demising and partition walls. Post and beam structures with slab and ceiling panels offer more spatial flexibility, being the reasonable choice for offices and commercial functions. Due to the normal complexity of architectural programs, the choice for mixed solutions is frequent. The use of panelised cores with stairs, elevators and washrooms is balanced with open spaces organized within a spatial grid of Glulam columns.
Sometimes wooden buildings appear as hybrid structures, meaning that they use wood and other structural materials like concrete or steel. The choice for a hybrid structure may be due to different reasons: code requirements, economy, or just because of architectural or structural design choices (like unusual overhangs or the need for stiffness). Because these buildings are a sum of components made of different materials, the interface between them, can be challenging due to the difference in their tolerances.
SOM launched in 2014 a research project “Timber tower research project” where “the goal (..) was to develop a structural system for tall buildings that uses mass timber as the main structural material and minimizes the embodied carbon footprint of the building.”. Their line of investigation points to the use timber combined with concrete and/or steel.
From the point of view of architectural design tall wood buildings tend to have the same formal limitations of steel or concrete structures. What perceptually differentiates them is the singular potential to express the wooden structure outside or inside, or either ways.
We can distinguish three main architectural design approaches to structure. First, we have the pragmatic line, the one that doesn’t care at all about the expressive value of wood, so for the sake of safety and durability, wooden structural elements are cladded and protected. A second attitude understands that a structural design should be expressed, at least in the interior of the building, if not for an ethical architectural principle, because of the aesthetical, the psychological and the health benefits. In a third group we can find the purists, maybe the inheritors of modernism, defending that a wooden structure should be expressed outside and inside. Some times this approach can led to a compromise as we can see in the 14 storey tall wood University of Toronto academic tower. The wooden structure is shown, but is also protected by a transparent skin.
The use of wood in external cladding is also a way to express the wooden technology and it can be used as a secondary level of design approach that can be included in each one of the main categories described previously. The more durable and safe solution would be obviously to opt for a non combustible skin. A smart choice was the one Waugh Thistleton used for the 2008 Stadthaus with the use of 5000 units of Eternit panels manufactured from 70% waste timber.
Most part of the first generation of wooden tall buildings tend to have a rational formal approach. Maybe wood alone doesn’t work as a driving force to a specific formal style (at least in the big scale). So, the formal quality of a wooden building, as well as in any other kind of building, will depend on the design skills of the authors.
Examples of interesting formal solutions are the 12 Storey Arbour project for George Brown College in Toronto designed by Moriyama & Teshima and Acton Ostry Architects, with structural engineers Fast + Epp, the 18 storey Port Living Building in Vancouver by Shigeru Ban, the 34 story C.F. Møller's tower for Stockholm, and the 12 storey Framework in Portland by Lever Architecture.
5 – Some tall wood facts
Based on the information gathered from a Summary report “Survey of International Tall Wood Buildings” (2014), for the owners and developers of ten international projects the most important reasons for pursuing a wood project are: the low carbon footprint, the building energy performance, the speed of construction and innovation and the market leadership. This last factor is not usually mentioned but it means that betting in a new technology and in new building expressions helps creating a leading position in the market.
We already mentioned the ecological advantages: wood elements in the building store carbon, they are made of a renewable material and they require low energy to be manufactured. According to Paul Fast the costs of wood buildings depend on the location, but usually tall wood construction costs are slightly higher (with 10% on the high side). However wood buildings can be built faster (estimated 25% faster) because they are prefabricated and because wood panels can be lifted directly from trucks (requiring smaller cranes due to the light weight), and sooner completion means sooner revenues. According to Andrew Waugh they require lesser building site traffic (up to less 80%), the construction works generate low noise and low waste, and there is no cure time as in concrete.
Bernhard Gafner, former structural engineer in Fast+Epp, says that, "A mass timber project is approximately 25 percent faster to construct than a similar project in concrete. Noting the advantages for urban infill sites in particular, he says it also offers 90 percent less construction traffic (trucks delivering materials) and requires 75 percent fewer workers on the active deck, making for a much quieter job site." The T3 Office building in Minneapolis, with 16700m2, was erected in 10 weeks, much faster than concrete and even faster than steel construction (according to Geral Epp).
Murray grove’s 8 CLT storeys were build in 27 days (more or less half the time of precast concrete). Its wood volume of 950m3 corresponded to a carbon sequestration of 760 metric tons, avoiding 320 metric tons of CO2. The Carbon savings were equivalent to take off the road 1615 passenger vehicles, or enough energy to operate a home for 803 years.
The lightweight of wood proved to be a great advantage in some cases. Wood’s choice for Forte, Victoria Harbor in Melbourne Australia by Lend Lease (completed in 2012) with 10 storeys was especially adequate because poor local soils required a lighter structure. The Bridport House in London, designed by Karakusevic Carson Architects had to deal with the complex requirements of having twice the number of units of the building that was on site before, but should had no more than 10% the weight because of the existence of a huge storm sewer below the site. Wood was obviously the logical choice.
Comparing to concrete and steel, dealing with wood on site is very convenient. Jay Zapata, TSM’s architect/job captain on the Wren Multifamily project in Los Angeles, says “Wood is a forgiving material, especially during the construction phase, since it allowed us to quickly resolve unexpected issues in the field without compromising our original design.”
Sources and more information:
“The development of a tall wood building” by Vittorio Salvadori https://issuu.com/salvadori.vittorio/docs/thesis_vittorio_salvadori_9719eae06a9d03
“A wooden tower: the seeds of an idea” by Ron Bakker https://www.trada.co.uk/publications/magazine-articles/a-wooden-tower-the-seeds-of-an-idea/
“Summary Report: Survey of international tall wood buildings” by Forestry Innovation Invesment and the Binational Softwood Lumber Council and Perkins+Will https://www.naturallywood.com/resources/summary-report-survey-international-tall-wood-buildings
“Timber construction returns to the city” by Jakob Schoof in Detail 1/2.2018 https://www.detail-online.com/
“The vertical timber city” by Peter Wilson https://www.trada.co.uk/publications/magazine-articles/the-vertical-timber-city/
“Tall wood buildings” by Michael Green https://www.amazon.com/Tall-Wood-Buildings-Construction-Performance/dp/3035604754
“Tall Wood” by Michael Green http://cwc.ca/wp-content/uploads/publications-Tall-Wood.pdf
“The Modern timber house in the UK” by Peter Wilson https://woodforgood.com/training-and-development/publications/the-modern-timber-house