Timber Towers: Building with Wood Could Reduce the Carbon Footprint of Cities
Wooden towers could reduce the carbon footprint of cities while offering urban dwellers the textured richness of a natural material.
Japanese architect Shigeru Ban is known for building structures using unconventional materials. Following the devastating 2011 earthquake in Christchurch, New Zealand, he built a Cardboard Cathedral using 98 equally sized cardboard tubes and eight steel shipping containers. The simple A-frame structure is said to be one of the city’s safest, earthquake-proof buildings. “The strength of the structure has nothing to do with the strength of the material”, Ban has said.
For a new project in Vancouver, Canada, the architect is using timber. The upcoming condo tower named Terrace House is slated to rise near the water in the upscale downtown neighborhood of Coal Harbour, and according to developers PortLiving, it will be the tallest hybrid timber structure in the world. “We are extremely excited by Shigeru Ban’s decision to bring his craft to the Pacific Northwest”, says Macario Reyes, founder and CEO of PortLiving, adding that the project marks a “global benchmark for timber design and livability”.
Although further details about the Ban-designed structure have not yet been released, an initial rendering shows a glass-clad tower with a sloped roof. A timber frame locally sourced from BC Wood will form the building’s upper portion and will be supported by a concrete and steel core.
Unlike his foray into paper tubing and milk crates however, Ban is not unique in selecting timber for the project. In recent years architects, engineers and developers the world over have been experimenting with proposals for tall wooden towers. In cities like Vancouver, New York and Hong Kong, which are known for soaring towers of glass and steel, a pre-industrial building material may seem of little use. However, wood proponents say it is an ideal material for an urbanising population, where the challenge is to accommodate ever-denser cities while reducing the carbon footprint of concrete, steel and other conventional building materials.
“Wood is unique because it is a renewable resource that sequesters carbon”, explains Thomas Robinson, a principal at Portland based Lever Architecture. His studio is currently building Framework, a 12-storey mixed-use project that combines engineered wood with a conventionally reinforced concrete mat foundation. “As trees grow, they absorb and store carbon”, he says. “Wood continues to hold this carbon even after being transformed into a building product. New trees planted to replace those harvested continue this cycle of sequestration”.
However, the material being used for tall-wood structures bears little resemblance to the logs in your old country cabin. Architects and builders now work in the realm of “mass timber”, a form of construction that uses large, prefabricated wood elements like nail-laminated timber, glued-laminated timber, or cross-laminated timber.
Cross Laminated Timber (CLT), the most common form of engineered wood, is made from layers of wood (typically three, five, seven, or nine) that are oriented perpendicular to one another and then glued together to form large, dimensionally-stable structural panels that can be prefabricated and assembled on site. (Another perk for city residents: since most mass-timber elements are fabricated before they reach the building site, there’s less dust and noise that usually accompanies the pouring of concrete and bending of rebar).
“The science of wood construction has come a long way in the past several decades”, says Chris Sharples, a principal at SHoP Architects in New York. His studio is developing plans for a new building at 475 W. 18th Street in Manhattan that will be built entirely of wood. With new high-tech products like CLT, Sharples says nearly every element of the building, right down to the elevator core, can be constructed in wood.
There are aesthetic advantages too. While most modern buildings attempt to conceal their structural, load-bearing features, wood is a natural material that people like to touch and proponents of wood buildings say wood surfaces could come to be seen as a mark of authenticity, much like the exposed bricks and irregular floorboards that people show off in renovated loft spaces. At Framework in Portland, wood columns and CLT ceilings will frame the building’s lobby and the apartments’ ceilings, creating a warm, textured look. “Wood gives the interiors great richness”, says Lever Architecture’s Thomas Robinson.
Europe is also actively exploring tall timber designs. In April 2016, plans were revealed for an 80-storey, 985 ft. tall wooden building integrated within London’s Barbican Centre. “If London is going to survive it needs to increasingly densify”, says Dr. Michael Ramage, Director of Cambridge’s Centre for Natural Material Innovation who worked on the scheme with PLP Architecture and engineers Smith and Wallwork. “One way is taller buildings. We believe people have a greater affinity for taller buildings in natural materials rather than steel and concrete towers”.
In Bordeaux, France, architect Jean Paul Viguier is designing a new housing and office complex that proposes a trio of timber-framed towers. The 182,000 sq. ft. scheme includes three blocks of engineered timber structures and an 18-storey tower that could become the world's tallest modern timber-framed building.
Over in Amsterdam, global consulting firm Arup was recently selected to develop HAUT, a 21-storey building in Amsterdam that could also become one of the highest wooden residential buildings when completed later this year. Designed by Team V Architecture, the 239 ft. scheme will include 55 apartments with wooden ceilings and balconies that protrude at the sharp corner facing the River Amstel. More than three million kilos of carbon dioxide will be stored in the cross laminated timber used to build HAUT, the architects say, an important step toward the carbon-neutral city.
Of course, building with wood does present its own set of challenges. Fire concerns are one potential barrier to acceptance, although wood advocates say modern wood products aren’t as hazardous as they might seem. It’s a bit like throwing a large log on the fire, says David Farnsworth, a structural engineer at global consulting firm Arup: The outside will burn first, forming what engineers call a “char layer”, but the inside will survive far longer. “When steel heats up, it softens and sags quite significantly,” says Mr. Farnsworth, “whereas timber actually performs better. It doesn’t lose as much of its stiffness. It’s counterintuitive”.
Height is another obstacle. In Europe and Canada, considered the leaders in the field, tall-wood structures tend to average around 10-storeys. For wood towers to exceed this height, further innovation will be required to strengthen the connection between beams and columns, which are critical for handling wind and seismic activity. To date the tallest wooden building is a 14-storey apartment block in Bergen, Norway. However, with developers in North America and Europe billing their upcoming projects as the tallest timber tower in the world, this record seems set to be broken.
This story appeared in the winter issue of Palace