Wooden buildings become fashionable in the trend towards decarbonization

Turning heads in a commercial district in downtown Yokohama, the Port Plus building is constructed solely of neat wooden columns and beams instead of the standard steel and concrete.

The 44-meter, 11-story Port Plus, located near the Kanagawa Prefectural Government Office, is the tallest fire-retardant architecture made entirely of wood in Japan. It was completed in March of last year.

By comparison, the famous five-tiered pagoda at Horyuji Temple in Nara Prefecture, the country’s oldest extant wooden structure, stands 32.5 meters tall.

Upon entering Port Plus, a training facility for Obayashi Corp. employees, visitors will smell the fresh scent of the trees. All sections there, including the seminar room, lounge, and sleeping space, are characterized by the solid, warm feel of wood.

The wood used totaled 1,990 cubic meters and between 60 and 70 percent of the material was produced in Japan.

DISADVANTAGES TO OVERCOME

Pure wood buildings like Port Plus, whose pillars, beams and other components are made of wood, are increasingly finding a market in Japan.

Major general contractors and home builders are getting on board, putting up wooden buildings that can withstand fires and earthquakes.

As the demand for buildings derived from wood grows in the context of the growing awareness of the need for decarbonisation, a pending challenge involves their high prices.

However, an estimate by Obayashi shows that carbon dioxide emissions related to the introduction of the facility are a quarter of those of its reinforced concrete counterparts and half of those of steel-framed buildings.

To improve the seismic resistance of the building, the pillars and beams are made up of interconnected cross-shaped units. Special wood with enhanced strength was used for the unit to boast a three-layer structure, with seismic isolation technology adopted as well.

Port Plus meets fire retardant standards at the same time. Now that Obayashi has developed Japan’s first wooden column that can survive fire for three hours, pure wood buildings of up to 15 stories or higher can be erected under the Building Standards Law.

“We successfully presented how far we can go with pure wood construction, revealing its potential,” said an Obayashi representative.

Mass production of this type of structure, however, is not currently under consideration, given the wealth of techniques and expense that must be invested in it.

Structural elements alone cost 30 to 40 percent more than steel-framed buildings, because the expense of meeting fire and other process criteria is particularly costly.

AQ Group, a homebuilder formerly known as Aqurahome Corp., strives to reduce construction costs by offering consumers first all-wood five-story buildings.

In November last year, AQ Group built a “general use” housing model in Kawasaki.

AQ Group, which prides itself on the supply chain formed through its involvement in custom log home construction, is looking to reduce the installation cost of its five-story log building to two-thirds of that of frame installations. steel and reinforced concrete.

Toshiya Miyazawa, president of AQ Group, who previously worked as a carpenter, said that developing a technical manual still represents a challenge for the large-scale commercialization of the company’s brainchild.

“Only a limited number of trained engineers can build” such a building from now on, Miyazawa said.

AFFORDABLE HYBRIDS

Recently, an increasing number of buildings have been constructed using wood and other materials.

According to the Ministry of Lands, 36 applications, 15 more than the previous year, were submitted for the construction of wooden buildings with four or more stories above ground in 2022. This compares with a paltry two 10 years ago.

Particularly on the rise are hybrid timber structures using timber, steel and reinforced concrete frames. Data from the Forestry Agency shows that at least 22 of these buildings with six or more stories will be completed by fiscal year 2028.

Mitsui Fudosan Co. and Takenaka Corp. plan to build a 17-story office building in Tokyo’s Nihonbashi district that will be 70 meters tall by 2025.

Sumitomo Forestry Co. is moving forward with a project to install a 350-meter skyscraper in which 90 percent of the structure will be made of wood by 2041 at the earliest.

An increasing number of contractors are building more affordable wood-based hybrids than their pure-wood counterparts, hoping to attract tenants who value the environmental sustainability of their offices.

Wood is most often applied to interior fittings and exterior walls of office buildings as employers seek workplaces that are more beneficial to the health of their employees.

Expectations are growing that the trend could revitalize forestry and other industries in rural communities.

As wooden buildings are likely to help decarbonisation efforts, the government is extending support and offering subsidies to cover construction costs and timber procurement.

As trees planted in forests after the end of World War II have come to absorb less CO2 due to their advanced age, their use as building materials will continue to keep the carbon absorbed in themselves.

Another reason for the government’s aggressive stance is that planting young trees after felling the older ones will help increase CO2 uptake.

A Forestry Agency official expressed high hopes for taller buildings.

“Taller buildings result in longer use of wood than shorter structures for residential purposes,” the representative said. “We will further contribute to decarbonization by making them much more common.”

To promote the use of wood, a government ordinance will be revised in April to reduce the standard fire resistance time from two hours to one and a half hours for certain floors inside wooden buildings.

The change is anticipated to help reduce construction costs.