Drawing all eyes in a business district in downtown Yokohama, the Port Plus building is fashioned solely from tidy wooden columns and beams instead of the standard steel and concrete. 

The 44-meter, 11-story Port Plus, located near the Kanagawa prefectural government’s office, is the highest fireproof architecture created entirely of timber in Japan. It was completed in March last year. 

In comparison, the famed five-level pagoda of Horyuji temple in Nara Prefecture, the nation’s oldest existing wooden structure, stands 32.5 meters tall. 

Stepping into Port Plus, a training facility for Obayashi Corp.’s employees, visitors will smell the fresh aroma of trees. All sections there, including a seminar room, lounge and bed space, are characterized by the solid and warm feel of wood.

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

DRAWBACKS TO OVERCOME

Pure-wood buildings such as Port Plus, whose pillars, beams and other components are all made of lumber, are increasingly finding a market in Japan.

Leading general contractors and homebuilders are jumping on board, putting wooden buildings that can withstand fires and earthquakes into place.

As demand is growing for timber-derived buildings against the backdrop of the increasing awareness of the need for decarbonization, a remaining challenge involves their hefty price tags.

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

To enhance the building’s seismic resistance, pillars and beams are comprised of cross-shaped units connected with each other. Special wood with improved strength was utilized for the unit to boast a triple-layered structure, with seismic isolation technology adopted as well.

Port Plus meets fireproof standards at the same time. Now that Obayashi has developed Japan’s first timber column that can survive flames for three hours, pure-wood buildings as tall as 15 or more stories 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 kind of structure, however, is not under consideration at present, given the wealth of techniques and expenditures that must be poured into it.

The structural elements alone entail 30 to 40 percent higher costs than steel-framed buildings, because expenditures to meet anti-fire criteria and other processes are particularly costly.

AQ Group, a housing builder formerly known as Aqurahome Corp., is scrambling to lower construction costs by pitching five-floor buildings created entirely of wood first and foremost to consumers. 

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

AQ Group, which prides itself on the supply chain formed through its involvement in building custom wooden houses, is looking to reduce the installation expenses of its five-story wooden building to two-thirds of that for steel-frame and reinforced concrete facilities.

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

“Only a limited number of skilled engineers can build” that type of building as of now, said Miyazawa.

AFFORDABLE HYBRIDS

An increasing number of buildings have recently been constructed utilizing wood and other materials. 

According to the land ministry, 36 applications were filed, up 15 from the previous year, for the construction of wooden buildings with four or more floors above ground in 2022. This compares with a paltry two 10 years ago.

Particularly on the increase are wood-hybrid structures utilizing timber, steel frames and reinforced concrete. Data from the Forestry Agency show at least 22 such buildings with six or more stories will be completed by fiscal 2028.

Mitsui Fudosan Co. and Takenaka Corp. are planning to erect a 17-story office building in Tokyo’s Nihonbashi district that will stand 70 meters high in 2025.

Sumitomo Forestry Co. is forging ahead with a project to install a 350-meter high-rise in which 90 percent of the structure will be fashioned from lumber in 2041 at the earliest.

An increasing number of contractors are building more affordable wood-based hybrids than their pure-timber counterparts, with the hope of attracting tenants that value their offices’ environmental sustainability.

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

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

With wooden buildings possibly assisting in decarbonization efforts, the government is extending support and offering subsidies to cover construction and timber procurement costs. 

As trees planted in forests following the end of World War II have come to absorb a smaller amount of CO2 due to their advancing age, their use as building materials will continue to keep absorbed carbon in themselves. 

Another reason for the government’s aggressive stance is that planting young trees after cutting down older ones will contribute to the boosted absorption of CO2.

A Forestry Agency official expressed high hopes for taller buildings.

“Higher buildings result in a more prolonged use of timber than lower structures for residential purposes,” said the representative. “We will be contributing further to decarbonization, making them much more common.”

With the aim of promoting lumber use, a government ordinance will be revised in April to shorten the fire resistance standard time from two hours to 1.5 hours for certain floors inside wooden buildings.

The change is anticipated to help reduce construction costs.

(This article was written by Go Takahashi and Sho Hatsumi.)