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Japan's high-rise condos not prepared for floods

High level of safety against tremors caused by winds, earthquakes required but not flood damage

Tokyo

THE number of Japan's high-rise condominiums has been increasing, mainly in urban areas, but their vulnerability to flood damage has become much more apparent.

A lot of effort has been put into preparing for earthquakes. However, torrential rains brought by October's Typhoon No 19 caused flooding of underground electrical equipment at some high-rise condominiums, which led to elevator and water outages, leaving residents on upper floors at risk of being isolated.

Municipalities, residents and others concerned are required to review anti-disaster measures in order to prepare for unexpected situations.

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High-rise condominiums generally refer to residential buildings that have a height of 60 m or more and 20 floors or more.

In the 1997 revision of the Building Standards Law, communal areas such as stairs and corridors were excluded when calculating a floor-area ratio, which is a ratio of the total floor area of the building to the site area.

As a result, it became possible to construct high-rise buildings equipped with luxurious communal spaces, and the number of such buildings increased.

According to Tokyo Kantei Co, a real estate research company, some 1,096 high-rise condominiums were constructed from 2000 to 2018.

Including those constructed before 2000, there were 333,789 units in 1,289 high-rise condominiums in Tokyo and 35 other prefectures, as at the end of 2018.

Of these, 80 per cent are concentrated in the Tokyo metropolitan area and the Kinki region. The total number of high-rise condo units is almost equal to the number of households in the ordinance-designated city of Hamamatsu - that is, about 330,000.

Super high-rise buildings, including high-rise condominiums, are required to ensure a high level of safety against tremors caused by earthquakes and winds.

The central government certifies the strength of each individual super high-rise building by checking things such as whether or not the building is strong enough to endure a long period of ground motion, which severely shakes high-rise buildings.

Those buildings are required to be resistant against wind speeds 1.25 times greater than the reference wind speeds specified for their respective regions.

In Okinawa Prefecture, with the nation's highest reference wind speed at 46 m per second, high-rise condominiums are required to withstand a wind speed of 57.5 m per second.

On the other hand, there are no regulations concerning flood damage because flooding does not cause structural issues, according to a source close to the Land, Infrastructure, Transport and Tourism Ministry.

However, in the recent Typhoon No 19, a high-rise condominium in the Musashi Kosugi district of Kawasaki was flooded and its underground electrical equipment broke down.

According to a major general contractor, lower floors of condominiums are used by stores, offices and other facilities, and electrical equipment is generally placed in the basement.

In Minato Ward, Tokyo, which is home to 73 high-rise condominiums, the largest number for a single municipality in the country (as at the end of 2018), the ward office asks each household to prepare enough water, food and sanitation kits for a minimum of seven days in case of elevators breaking down due to earthquakes.

However, "we do not expect measures to be taken against flooding", said a senior official at the ward office.

In anticipation of long-term power outages in the wake of earthquakes, an anti-disaster network of 18 high-rise condominiums in coastal areas of Tokyo's Chuo and Minato Wards and other places signed a contract with a fuel company to allow them to fuel emergency generators from ships on the sea.

Fourteen of the 18 condominiums have their electrical equipment and emergency generators in basement.

In another 37-storey condominium in Tokyo's Chuo Ward, which is surrounded by the Sumidagawa river and Harumi Canal, its basement floor was flooded by Typhoon No 15 in September, and one elevator stopped working.

According to the head of a neighbourhood association, there are boards to prevent the ingress of water into the basement, but they have not been used for about 20 years. WP