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On uneven ground: landfill property pitfalls

by Philip Brasor and Masako Tsubuku

After the real estate agent unlocked the front door, the musty smell told us that the house had not been aired for some time. He laid out slippers for us and proceeded to raise the shutters and open the windows. Then, upon entering the kitchen he exclaimed, “Katamuite iru” (“It’s uneven”).

We took out a small carpenter’s level we carry when inspecting properties and placed it on the floor. The bubble was within the lines, indicating the floor was level, but as we moved it toward the east wall, it moved. By the time we got to the wall, the bubble had traveled west, out of the comfort zone. The floor was inclining downward to the east.

The house was built in 1988 and had been renovated at least once since then. The agent expressed puzzlement that the previous owner hadn’t corrected the problem, and when we asked him how much it would cost to do that he said, “About ¥10 million.”

During the 2011 Great East Japan Earthquake, liquefaction occurred in certain regions, causing structures there to sink and tilt. The only recourse was to jack up the structures to make them level again. But the house we were inspecting was not a victim of liquefaction. It was worse. When the soil under a house liquefies, the house may sink but the integrity of the structure usually isn’t affected. In this case, however, the ground underneath the house was not firm enough to begin with, and over time it had shifted, causing structural changes in the actual house. That’s because it was built on land that had been artificially elevated by adding soil and then secured with a yōheki (retaining wall). We’d seen this problem before.

Japan is a mountainous country. Only 23 percent of its land mass is level, which is why so much of the terrain has been altered over the years. Hills have been terraced and flattened; inlets, bays, marshland and valleys filled; rivers redirected. The coastal regions of the Osaka-Kobe metropolis and Tokyo Bay are made up of extensive landfill. The Kanto Plain is actually a basin containing river-borne alluvial sediments and plateaus covered with volcanic loam. We’ve heard more than one geologist refer to it as “a bowl of jelly.”

About 13 percent of Japan’s land is reserved for farming, and it’s difficult to change designations from agricultural to residential. Housing land is precious, which explains why plots tend to be small and developments cramped. It also explains the ubiquity of retaining walls. Because so many houses are built on tracts that were once rolling hills, summits are lopped off (known as kiri-do) and the removed soil is used to fill intervening depressions (mori-do).

In some developments, the hills are kept as they are and the plots have been terraced with retaining walls that can rise as high as 5 meters. If the walls are properly anchored and pipes are installed to drain off groundwater, the house should remain level as long as it stands, but stricter codes for land preparation were only enacted in the past two decades, and even then they haven’t always been enforced properly.

According to the land ministry there are some 13,000 “residential areas” in Japan that have been altered through kiri-do and mori-do construction. Most of them were created during Japan’s accelerated growth period between the 1960s and the 1980s, when there was intense demand for single-family homes in the suburbs of major cities. As more of these properties go on the market because their owners are retiring or dying, the problem of unlevel structures has become more apparent — but what really made the issue topical was the 2011 Great East Japan Earthquake.

Last month, NHK aired a special about houses in Miyagi Prefecture city of Sendai that had shifted during the quake, some by as much as 2 meters. Almost all these structures were built on kiri-do/mori-do plots with the help of retaining walls. The damage to some houses was too great to repair, but many could be salvaged. The problem is that as the land shifted, so did the property lines, meaning that some houses are now effectively within their neighbors’ properties. This meant that before owners can go about repairing structures they have to work out with their neighbors new property lines — and some of those neighbors insist that the houses are moved back to where they started from. That kind of work can be very expensive. Had the houses been built on land that was level to begin with, this would not have been a problem.

But even before the earthquake, the government acknowledged that mori-do plots would become a problem over time, and the land ministry asked prefectures and municipalities to draw up geological maps showing where land had been altered for housing and how it had been altered. The aim is to eventually inspect these areas and carry out work to make them safer and more stable.

According to NHK, however, so far only one-third of local governments have even done the surveying. The problem they envision is that property owners won’t want the fact that their houses may be built on weak land publicized, since that would negatively affect the value of the land. And in many cases it was local governments that developed these areas, so they worry about possible lawsuits. Also, it is estimated that just checking the land will cost them about ¥3.5 billion.

Most housing erected in the last 15 years or so is safe. That land has been prepared properly and retaining walls built to exacting standards. But anyone looking to buy older properties will be at a disadvantage since most realtors don’t have information about the land beneath the structures.

That’s why we were surprised when the agent so clearly indicated that there was a problem. He obviously understood that this house was not level right away and made us aware of the fact, knowing full well that it would likely kill the sale. Then again, part of the property’s appeal was its elevated situation. It sat on a corner and looked out above its neighbors’ roofs in three directions. Sometimes, an aspect that makes a house more aesthetically appealing also makes it more dangerous.


What to look for when checking out the land

  • Concrete retaining walls are more effective than block or stone walls, which used to be the standard and are still common.
  • According to law, for every 3 sq. meters of retaining wall there must be at least one drainage outlet.
  • Retaining walls with cracks or vegetation coming out of the drainage outlets often indicate that the ground isn’t stable.
  • Reinforcement of existing mori-do (filled land depression) plots costs between ¥400,000 and ¥600,000, depending on the size and shape of the house being built on the plot.
  • Developers often use the words “oka” (hill) or “dai” (table) in the name of a development to mask the fact that it was built on low land or mori-do. Realtors don’t always offer this information, so potential buyers should check with the land office of the local government to find out how the land was prepared. Flood maps are also helpful.

Philip Brasor and Masako Tsubuku blog about Japanese housing at www.catforehead.wordpress.com.