Buying a Home in Japan

Top 3 Factors That Affect a Building’s Earthquake Resistance: What to know before you buy a home in Japan

By Jeff Wynkoop

Most buyers in Japan are aware of the importance of assessing earthquake risk before buying a home here. As the events of March 11, 2011 and the earthquake of June 18th, 2018 in Osaka again showed us, Japan is a nation of natural disasters, and earthquakes (and resulting tsunamis) can represent a grave risk to any homeowner in Japan.

Three Different Building Standards

When buying either a pre-owned condo or free-standing house in Japan, initially it is important to know whether the building was completed:

  • Before 1981
  • Between 1981 and 2000
  • After 2000

The reason this is important is that the building standards law was changed significantly in 1981 and again in 2000. Residences completed after 2000 are subject to stricter construction codes for earthquakes than residences completed between 1981-2000, and residences built before 1981 were built subject to even looser construction standards.

If the building was completed in 1981-83, be sure to have your agent confirm the date of application for certification of the building plans (建築確認申請受理日), because only buildings with a date of application of June 1, 1981 or later are subject to the more stringent Building Standards Law. It depends on the size of the project, etc., but buildings are usually completed within one to two years of the date of application. The completion date of the building (建物の完成(竣工)年月), not the date of application however, is usually what is advertised to potential purchasers.

For more on Japan’s earthquake building codes, please see: Earthquake building codes and technology in Japan

What are the three main factors that affect a building’s earthquake resistance?

The market for both new and resale homes has grown at a brisk pace over the last five years, and there are fewer and fewer affordable properties on offer. This has caused more homebuyers to look at buying a property that was built prior to 1981.

How can a homebuyer understand earthquake risk in these buildings? Are all buildings built prior to 1981 prone to massive damage in the event of an earthquake? Is a post-1981 house always better than a pre-1981 house for earthquake risk?

There are three main factors when assessing the earthquake resistance of a building:

  1. Structural resistance arising from the design of the building itself
  2. The level of workmanship (the existence of construction defects) and/or use of low-grade or defective materials during construction
  3. The extent of maintenance of the building over time, including an assessment of the level of wear and tear in the building since completion of construction and/or refurbishment.

Are all buildings built prior to 1981 less earthquake resistant than newer ones?

It is important to know that there are plenty of buildings built before 1981 that were designed and constructed with earthquake resistance in mind.

In addition to design and construction, if the building has been regularly maintained and repaired over the years pursuant to a long-term maintenance strategy, the building may already satisfy the post-1981 building standards. As a rule of thumb, depending on the location, design, etc., pre-1981 homes can be as earthquake resistant as homes built 10 or even 20 years later.

When I did a homestay in Osaka many years ago, I lived with a family that had had its free-standing house designed and built for them. My host father was very proud of the fact that he had withheld no expense in having the house constructed especially earthquake resistant. He told me he had giant pillars put in under the house that went very deep into the ground. In fact, during the big 1995 Hanshin earthquake, the house in Toyonaka shook (all of the books on my desk were thrown to the ground), but there was practically no damage. Meanwhile, there were old houses a mere two blocks away that were totally destroyed (basically old wooden structures with huge and heavy tile roofs).

#1 Design of the building

Generally the easiest way to check the design of the building is to have a real estate professional such as an architect review a copy of the construction blueprints (竣工図面), which are finalized at the end of construction. The problem is, however, often the seller doesn’t have a copy of the construction blueprints, especially for older buildings. In this case, you will need to ask around at the local government offices, although construction blueprints are not always available. Before ordering a home inspection and incurring cost, there are a few factors anyone can look at when considering purchasing a residence.

a. Number and location of walls

Earthquake resistance involves surviving the initial horizontal earthquake shock. In order to withstand forces from the outside, the number and location of walls in the dwelling should be considered. It is also important to consider the balance of walls in the building. If one side has many thick walls, and another side has only a few, flimsy walls, the overall effect on the building will be instability.

b. Pencil buildings and buildings on small parcels of land

Buildings on small plots of land are often designed to reduce the size and number of walls in the house in order to have more livable space. This is especially true of small buildings where there is a parking space in front. If the building and entrance area is small but the plot of land is large, usually the building will be designed with the parking space as a separate area (i.e. not taking space away from the dwelling). In any event, be sure to look at the sufficiency of the walls that face the parking space (are they extra thin for more parking space?).

c. Corner windows

Windows at the corner of a structure generally lead to less structural integrity. Buildings with corner windows that stick out, like bay windows, are even less sturdy.

d. Internal stairways and rooms with high ceilings

Houses with rooms with high ceilings, for instance a house with a sunken living room, generally do not withstand horizontal shocks very well. Internal stairways are also not very stable. As a rule, any break in the floor plate will lead to a less earthquake-resistant building.

e. Old, wooden three-story structures built on narrow plots of land

Relatively speaking, buyers of old, wooden, three story dwellings tend to run into the most defect trouble. This is just an anecdotal observation however, and does not apply in every case. New three story houses are built with the extra design and care needed for earthquake integrity. If you find an old, wooden, three story house with a narrow base on a small plot of land, with lots of protruding corner windows, and numerous internal stairways and high ceilings, constructed before 1981, you should carefully consider whether the time and expense of arranging for a house inspection makes sense in your case.

f. Physical location of the house

Is the house located in a high-risk earthquake zone? The following links lead to Japanese pages that provide official government assessments of potential natural disaster risk.

Earthquake risk

Tokyo Metropolitan Area earthquake assessment risk by city and town (Japanese)

What is the probability of an earthquake striking your neighborhood in Japan? (English)

Flood Zone

Is the building in a flood zone? (Japanese)

Liquefaction risk

Is the building in a known liquefaction risk area? Liquefaction refers to soil becoming ‘liquid-like’ during an earthquake (usually land fill or reclaimed land), oftentimes leading to significant loss of life and property.

Tokyo Metropolitan Area liquefaction forecast 

g. Foundation

Is the building in an area of town where the soil and foundation is hard? Land that is not very hard transfers the force of the earthquake more directly to buildings above.  The Geospatial Information Authority of Japan publishes a map in Japanese (called the 土地条件図) where you can find out if an address is located on an elevated area (台地), where the foundation is generally hard and flooding and liquefaction less likely. However, buildings specified as being on built-up land (盛土) in elevated areas are less desirable.

#2 The level of workmanship and existence of construction defects

Once you are satisfied with review of the design of the property, it is important to learn about the existence or non-existence of construction defects in the property. Succinctly, was the property constructed in accordance with the design plans? Were the materials used at the time of construction the highest grade? Construction defects are typically not easy to find, and most purchasers will need to arrange for a home inspection by a real estate professional for this level of review. Although the seller’s agent will provide you with the names of several home inspectors, it is highly recommended for the buyer to independently find and hire a home inspector to avoid any latent conflict of interest between the seller’s agent and the inspector.

#3 Level of maintenance over time

Sometimes the level of wear and tear in a building is obvious. However, like understanding the level of workmanship/existence of construction defects in a building, in order to truly understand the relative level of wear and tear, you will need to hire a real estate professional to carry out a home inspection. Even if a property is well-designed, and constructed with due care using high-grade construction materials, buildings degrade and break down over time. Without a regular maintenance plan, even the best property soon becomes undesirable.


Lead photo: Watari, Miyagi prefecture on the third day (March 14, 2011) after the Great East Japan earthquake and tsunami. A helicopter from the Ground Self Defense Force rescues a person isolated by a tsunami. Source: Wikimedia