When the Washable House is flooded, dirty water and mud can be washed away by flushing water through spaces between the inner and outer walls. (Provided by the Reproduction Conference of Home and Town)

Photo/Illutration Yuji Koyama displays a model of the Washable House in Kawaguchi, Saitama Prefecture. (Saori Kuroda)

SAITAMA--Inundation from flooding caused by torrential rains no longer has to be the nightmare many homeowners fear in disaster-prone Japan.

Building experts have developed a “washable” house that can be rendered fit to live in, rather than being torn down, in such cases.

A typical wooden home has to have its inner and outer walls replaced after being inundated, and doing so costs nearly 10 million yen ($91,000) and produces a lot of waste.

There is no way to drain water and remove dirt once they seep into the frame and building materials.

However, the foundation, pillars and heat insulators of the Washable House are made with water-proof materials, allowing the structure to remain livable even after being repeatedly flooded.

Dirt and lingering odors can easily be removed when the surfaces are cleaned, according to the Reproduction Conference of Home and Town, which developed the innovative style of housing.

Only indoor walls need to be replaced to ensure a hygienic environment is restored.

With the majority of components remaining intact, estimated post-flooding repair costs can be reduced to about 2.5 million yen, the association said.

The association, consisting of professionals such as architect offices, building contractors, building materials supplies, a lawyer and a professor specializing in urban planning, provides consultations on construction work.

The project was initiated by architect Yuji Koyama, 74, who serves as a director of the association, after he was asked by his daughter and her husband for advice on protecting their new home from flooding.

According to a hazard map prepared by the land ministry, the construction site of their home in Kawaguchi, Saitama Prefecture, sits in an area that can be inundated with floodwaters of between three and five meters if the Arakawa river overflows its banks.

The association set about designing a home to minimize damage and ensure it can be restored after being flooded.

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The Washable House can be cleaned by flushing water through a hose inserted into spaces between the inner and outer walls. (Saori Kuroda)

A space of several centimeters separates the inner and outer walls, which allows for clean water to be flushed through to remove dirty water and mud.

The kitchen and washroom are also detachable, making it easy to wash off dirt from the in-between spaces.

An air blower is installed inside the structure to deliver solar heat collected from the roof to dry the spaces under the floor and between the walls.

“The house can be reused without producing a lot of waste,” Koyama said. “It also lives up to the ideals of Sustainable Development Goals.”

Koyama said he was spurred to develop the Washable House due in part to a longstanding practice in Japan of demolishing houses after one generation even though they can last for 100 years.

The average lifespan of houses is about 55 years in the United States and 77 years in Britain, according to the land ministry. In contrast, the figure for Japan is about 30 years.

Koyama added that the Washable House meets the highest Grade 3 rating for quake resistance strength standards and can last for 100 years if properly maintained.

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