[INTERVIEW] The case for building cities out of wood

The Hangreen, a 19.1-meter building mostly made of wood, stands in Yeongju, North Gyeongsang Province. The five-story structure symbolizes the new trend of eco-friendly construction in Korea. Korea Times photo by Kim Kang-min

Korea embraces timber as key construction material

By Jung Min-ho

Korea Forest Service Deputy Minister Choi Byeong-am speaks during a recent interview with The Korea Times at his office in Daejeon. Korea Times photo by Kim Kang-min

YEONGJU/DAEJEON ― For more than a century, concrete and steel have replaced wood as primary building materials, especially for tall structures. But thanks to increasing demand for "greener construction" and technological advances, timber is back in style.

The Hangreen, a 19.1-meter wooden building in Yeongju, symbolizes the new trend in Korea. The five-story structure, mainly made of Korean larch, a common tree species here, marks only the beginning of a new era of architecture, according to Choi Byeong-am, deputy minister of the Korea Forest Service (KFS).

"Imagine a wooden skyscraper in the heart of Seoul," Choi said. "You may see it in the near future. Wooden buildings are more eco-friendly, sustainable and aesthetic than concrete ones. Increasingly, people are rediscovering the value of the old material."

The interior of the Hangreen / Korea Times photo by Kim Kang-min

The biggest development in timber construction of the past few decades is "mass timber," which refers to composite-wood systems that combine multiple layers of planks into larger structural elements; cross-laminated timber (CLT), its most common form, makes it possible to build tall buildings by offering high strength.

So, in theory, architects and engineers today can build a modern town ― or an entire city ― mostly out of wood. This is one of the plans Choi has in mind.

"In collaboration with the Ministry of Land, Infrastructure and Transport, we are planning to select a few towns or cities (most likely three) next year and will transform them into sort of like wooden towns or cities as part of the government's urban renewal projects," he said.

"To make it possible, we should ease regulations on wooden structures, including the height limit of 18 meters (the Hangreen was an exception), which the ministry has been considering positively. Besides, we need to improve our technology, which, at the current level, enables us only to construct a 12-story building (about 36 meters)."

The world's tallest timber building is the 18-story Mjostarnet tower in Brumunddal, Norway. Completed last year, it is 85.4 meters high and includes a hotel, offices and private homes. HoHo in Seestadt Aspern, near Vienna, Austria, is the second tallest at 84 meters. But Japan, another country known for its advanced wood construction technology, is planning to build a 350-meter tower in Tokyo ― a project expected to be finished in 2041 ― to challenge them.

According to the KFS, only 17 percent of wood used in Korea is domestic timber. But this is projected to increase to 30 percent by 2035, given that the country started a massive tree planting campaign about 50 years ago.

"Many trees will be mature enough to be used in the coming decade or so," Choi said. "This means Korea will soon enter a new era of opportunity."

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The 85.4-meter Mjostarnet tower in Norway is the world's tallest timber building. Courtesy of Vjus

Mass timber is sturdy as concrete and just as fireproof

One of the most popular misconceptions about wooden buildings is that they are a lot more hazardous than ones made of concrete and steel in the event of a fire.

But mass timber is not like dry sticks. It is difficult to ignite in the first place and, if a fire occurs, it takes quite a long time to burn completely. For instance, the Hangreen has a fire-resistance rating of two hours ― the duration that a material can withstand exposure to fire.

In addition, when the wood burns, it does so in a predictable way, unlike buildings made of concrete, steel, glass and other materials, which can suddenly explode or snap.

It is difficult to ignite mass timber. If a fire occurs, the wood burns slowly and predictably. Korea Times photo by Kim Kang-min

The bottom line is that there is no such thing as a "perfectly fireproof" building. All materials are combustible, albeit to varying degrees, and can pose a hazard to life and property.

"Concerns about wooden buildings' fire safety are overblown," Choi said. "Such worries will disappear as more people get to see and learn about modern wooden buildings."

Designed and built correctly, wooden buildings are also very durable. Across the world, there are many examples that have survived for hundreds of years with proper care.

Mass timber has proved to perform well in earthquakes. If damaged, the material can be repaired relatively easily; concrete buildings with extensive cracks are more difficult to fix.

In addition, wood is lighter and less time is required to build a structure from it.

"It would take twice as much time to build something like the Hangreen with concrete," Choi said. "Wood is more expensive ― about five to 10 percent higher. But lower labor costs for reduced construction time can help offset the material cost."

A dense forest in Yeongju / Korea Times photo by Kim Kang-min

Cutting down trees is not always bad for the environment

Cutting down trees for building material may sound bad for the environment. But this is not always true.

"Young trees can absorb and store far more carbon from the atmosphere than old ones," Choi said. "In a study, a 20-year-old tree absorbs more than twice as much carbon a year as a 60-year-old one does. So, replacing mature trees with new ones would actually be better for fighting climate change.

"Of course, tree-cutting on a large scale could lead to deforestation and hurt biodiversity in the affected region. So the key point is to balance it wisely with careful long-term planning."

Research shows that trees store carbon when growing and give off oxygen. After becoming wood products, such as furniture and buildings, they continue to store that carbon.

Trees are a renewable natural resource, different from other natural resources such as metal ores, coal, petroleum and natural gas, which are non-replaceable. Moreover, lumber byproducts such as sawdust and wood chips can be useful and are environmentally benign.

According to the KFS, a recent survey shows that 82 percent of respondents said they would support logging for the use of wood; although 72 percent said, in doing so, the environment should be considered first.

"We will continue to implement our selective logging policy and make the best use of forest biomass to improve the public understanding of wood construction," Choi said.