Wooden Skyscrapers Are on the Rise
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Wooden Skyscrapers Are on the Rise

Architects and builders turn to ‘mass timber’—an engineered wood product similar in strength to concrete and steel—to build multistory buildings.

By ERIC NIILER
Wed, Apr 13, 2022 11:16amGrey Clock 5 min

Guests at a new 20-storey hotel and cultural centre in Skellefteå, a former gold-mining community in northeastern Sweden, don’t have to step outside to feel immersed in the natural world. The floors, ceilings and support beams of the building—which also houses a museum and other facilities—are made almost entirely of spruce and pine harvested from nearby woodlands.

“When you come inside, the smell of the timber is almost like you enter a forest,” Robert Schmitz, a partner at an architectural firm in Stockholm and the building’s lead architect, says of the Sara Cultural Centre and Wood Hotel. “This is a really small city, and timber is something that everyone in this community has a connection to. They understand the material.”

The 30,000-square-metre complex is part of an emerging trend as architects, developers and builders turn to so-called mass timber, wood that is glued and pressed in special ways to make it similar in strength to concrete and steel and thus capable of replacing those building materials even for skyscrapers and other massive edifices.

Advocates of mass-timber construction maintain that it can be more environmentally friendly than conventional construction. The carbon footprint of a building constructed with sustainably harvested mass timber, which is made from trees that are selectively cut rather than clear-cut, can be half that of a similar building made of concrete and steel, according to an assessment of mass timber construction published recently in the journal Sustainability.

“If you look at the carbon impact of harvesting trees and turning them into buildings, it gives you a much better number than you get from concrete or steel,” says Stephen Shaler, a professor of sustainable materials and technology at the University of Maine. “As long as you have sustainably managed forests—and we have that capacity—it is a clear winner on the carbon footprint.”

The number of multistorey mass-timber buildings being built in the U.S. rose 50% between July 2020 and December 2021 to more than 1,300 structures, according to the wood trade group WoodWorks. Among the projects are an eight-storey office building in Charlottesville, Va., a new Google five-stoery office building scheduled to open in August in Sunnyvale, Calif., and a 25-storey residential-retail complex rising in Milwaukee. The International Building Code permits wooden buildings of up to 18 stories, but the developers of the Milwaukee project say they obtained a variance after submitting data to city officials showing it was as safe as a conventional building.

Even more ambitious projects may appear: A Japanese timber company has proposed a 70-story wood building for Tokyo, while a U.K.-based architectural firm has plans for an 80-story skyscraper in London.

To meet the demand for mass timber, 18 manufacturing plants have been built in the U.S. and Canada since 2014, according to the U.S. Forest Service. The global market for mass timber was estimated at $956 million in 2020 and is expected to grow at an annual rate of 13.6% from 2021 to 2028, according to a December 2021 report by Grand View Research.

In addition to potential environmental benefits, construction experts say mass-timber buildings can cost less than concrete-and-steel structures—especially if they’re sited near a manufacturing plant where pieces of the building are cut to order. With mass timber, for example, builders don’t have to pour concrete and wait for it to set. Mr. Schmitz and the team behind the Sara Cultural Centre say they saved a year in construction and labor costs as the wood panels and beams were made at a nearby plant.

Using mass timber cut the timeline for the Milwaukee complex, called Ascent, by about four months, says Tim Gokhman, managing director of the Milwaukee-based New Land Enterprises and the project’s manager. Because wood is lighter, only 100 support piles had to be driven into the site’s soft soil rather than the 200 that would have been needed for a similar concrete-and-steel building. And whereas pouring concrete floors might require 30 to 40 workers, he said, only 10 workers were needed to install the cross-laminated timber, or CLT, panels for each floor.

CLT is made by laying down and gluing together multiple wooden pieces oriented at 90-degree angles to one another and is commonly used for floors and walls. Another key type of mass timber, called glulam for glue-laminated timber, is commonly used for support beams.

“Each piece of wood is measured and has a designated place,” Mr. Gokhman says. “So as the building is built, you’re literally updating its progress in a digital world. Without that technology, you don’t have the same efficiency and schedule gains.”

Some point to limitations of mass timber, saying that buildings made with both conventional and mass-timber construction can have advantages over those made solely of wood or solely of steel and concrete.

“In a tall building, you really do want the base of it to be concrete, and as you go up in the building it gets lighter, and makes more use of wood,” says University of Oregon architecture professor Judith Sheine, who has designed buildings using both mass timber and concrete and steel. And conventional construction might be better in coastal areas, she says, adding, “If you’re in a flood zone, the base should still be concrete because getting wood wet is not that great.”

Some fear the mass-timber trend could spur timber companies to cut down old-growth forests that contain large amounts of carbon rather than selectively harvesting younger forests. They argue that calculations of the carbon footprints of mass timber buildings must include roots, branches and other parts of trees that are often burned as well as the fossil fuels consumed to cut down the trees, fabricate the wood products and transport them to construction sites.

“We’re not going to log our way out of the climate crisis,” says Jason Grant, manager of corporate engagement, forests, for the World Wildlife Foundation in San Francisco. “There are objective limits to how much timber we can produce and consume. We need to bear in mind the constraints that we need to operate in if we want to avoid climate disaster and stem nature loss.”

Seismic testing of a 10-storey tall wooden building scheduled to take place in California this fall could give a boost to the mass-timber trend. “We need to find a way to make these buildings earthquake-resistant, since it’s a new building type, and nobody’s ever done this before,” says Shiling Pei, associate professor of civil and environmental engineering at the Colorado School of Mines and the project leader for the shake test.

To minimize the risk of fire, builders and architects are incorporating precautions into mass timber buildings, says David Barber, a Washington, D.C.-based fire safety engineer with the multinational design, engineering and architectural firm Arup. He points to covering CLT wall and floor panels in taller mass timber buildings with fire-rated drywall rather than leaving them exposed, for example, and checking the fire rating for connection points between the timber panels as well as the glue connecting the panels and laminated timber.

“We want to make sure that the buildings are done in very conservative ways, so they are being designed to a very high level of safety,” says Mr. Barber, who has worked on both the Ascent building in Milwaukee and the eight-storey Apex building in Charlottesville.

Tests of a two-storey mass timber apartment conducted in 2017 at a Bureau of Alcohol, Tobacco and Firearms facility in Beltsville, Md., showed that it took longer to catch fire and retained its structural integrity longer than a similar wood-frame structure.



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I.M. Pei was the confident visionary behind such transformative structures as the Bank of China Tower in Hong Kong and the Louvre Pyramid in Paris, but he was also humble, and for years resisted a retrospective of his work.

Pei, a Chinese-American architect who died in 2019 at 102 , would always protest any suggestion of a major exhibition, saying, “why me,” noting, too, that he was still actively at work, recalls his youngest son, Li Chung “Sandi” Pei. A decade ago, when Pei was in his mid-to-late 90s, he relented, finally telling Aric Chen, a curator at the M+ museum in Hong Kong, “all right, if you want to do it, go ahead,” Sandi says.

A sweeping retrospective, “I.M. Pei: Life Is Architecture,” will open June 29 at M+ in the city’s West Kowloon Cultural District. The exhibition of more than 300 objects, including drawings, architectural models, photographs, films, and other archival documents, will feature Pei’s influential structures, but in dialogue with his “social, cultural, and biographical trajectories, showing architecture and life to be inseparable,” the museum said in a news release.

As a Chinese citizen who moved to the U.S. in 1935 to learn architecture, Pei—whose full first name was Ieoh Ming—brought a unique cultural perspective to his work.

“His life is what’s really interesting and separates him from many other architects,” Sandi says. “He brought with him so many sensibilities, cultural connections to China, and yet he was a man of America, the West.”

Facade of the Bank of China Tower in Hong Kong in a photograph commissioned by M+ in 2021.
© South Ho Siu Nam

Pei’s architectural work was significant particularly because of its emphasis on cultural institutions—from the East Building of the National Gallery of Art in Washington, D.C., to the Museum of Islamic Art in Doha, Qatar—“buildings that have a major impact in their communities,” Sandi says. But he also did several urban redevelopment projects, including Kips Bay Towers in Manhattan and Society Hill in Philadelphia.

“These are all places for people,” Sandi says. “He believed in the importance of architecture as a way to bring and celebrate life. Whether it was a housing development or museum or a tall building or whatever—he really felt a responsibility to try to bring something to wherever he was working that would uplift people.”

A critical juncture in Pei’s career was 1948, when he was recruited from the Harvard Graduate School of Design (where he received a master’s degree in architecture) by New York real estate developer William Zeckendorf.

With Zeckendorf, Pei traveled across the country, meeting politicians and other “movers and shakers” from Denver and Los Angeles, to Philadelphia, Washington D.C., Boston, and New York. “He became very adept at working in that environment, where you had to know how to persuade people,” Sandi says.

During the seven-year period Pei worked with Zeckendorf, the developer fostered the growth of his architecture practice, supporting an office that included urban, industrial, graphic, and interior designers, in addition to architects and other specialists, Sandi says.

When Pei started his own practice in 1955, “he had this wealth of a firm that could do anything almost anywhere,” Sandi says. “It was an incredible springboard for what became his own practice, which had no parallel in the profession.”

According to Sandi, Chinese culture, traditions, and art were inherent to his father’s life as he grew up, and “he brought that sensibility when he came into America and it always influenced his work.” This largely showed up in the way he thought of architecture as a “play of solids and voids,” or buildings and landscape.

“He always felt that they worked together in tandem—you can’t separate one from the other—and both of them are influenced by the play of light,” Sandi says.

View of the National Center for Atmospheric Research, on the mesa, in a photograph commissioned by M+ in 2021.
© Naho Kubota

Pei also often said that “architecture follows art,” and was particularly influenced by cubism, an artistic movement exploring time and space that was practiced in the early 20th century by Pablo Picasso, Georges Braque, and the sculptor Jacques Lipchitz, among others. This influence is apparent in the laboratory at the National Center for Atmospheric Research in Boulder, Colo., and at the Everson Museum of Art in Syracuse, N.Y. “Those two buildings, if you look at them, have a play of solid and void, which are very cubistic,” Sandi says.

Yet Sandi argues that his father didn’t have a specific architectural style. Geometry may have been a consistent feature to his work, but his projects always were designed in response to their intended site. The resulting structure emerged as almost inevitable, he says. “It just was the right solution.”

Pei also intended his buildings “not only to be themselves a magnet for life,” but also to influence the area where they existed. “He never felt that a building stood alone,” Sandi says. “Urban design, urban planning, was a very important part of his approach to architecture, always.”

After he closed his own firm to supposedly “retire” in the early 1990s, Pei worked alongside Sandi and his older brother, Chien Chung (Didi) Pei, who died late last year, at PEI Architects, formerly Pei Partnership Architects. Pei would work on his own projects, with their assistance, and would guide his sons, too. The firm had substantial involvement in the Museum of Islamic Art, among other initiatives, for instance, Sandi says.

Working with his father was fun, he says. In starting a project, Pei was often deliberately vague about his intentions. The structure would coalesce “through a process of dialogue and sketches and sometimes just having lunch over a bottle of wine,” Sandi says. “He was able to draw from each of us who was working on the project our best efforts to help to guide [it] to some kind of form.”

The M+ retrospective, which will run through Jan. 5, is divided into six areas of focus, from Pei’s upbringing and education through to his work in real estate and urban redevelopment, art and civic projects, to how he reinterpreted history through design.

Sandi, who will participate in a free public discussion moderated by exhibition co-curator Shirley Surya on the day it opens, is interested “in the opportunity to look at my father anew and to see his work in a different light now that it’s over, his last buildings are complete. You can take a full assessment of his career.”

And, he says, “I’m excited for other people to become familiar with his life.”