Risk Dictionary › 旧耐震

Pre-1981 seismic standard  /  Old Earthquake-Resistance Code

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What it means

Japan revised its Building Standards Act (建築基準法) on June 1, 1981, introducing what is now called the 新耐震基準 (new seismic standard). Any building that received its construction permit before that date was built under the old standard — 旧耐震.

The old standard required buildings to withstand a moderate earthquake without structural damage. The new standard goes further: a building must withstand a major earthquake (震度6強〜7) without collapsing, even if it sustains damage. The 1995 Great Hanshin Earthquake exposed just how significant this gap was — the overwhelming majority of buildings that collapsed were built under 旧耐震.

Why listings never tell you this

Platforms like athome, SUUMO, and HOME'S display the 建築年月 (build year and month), but they do not label properties as 旧耐震 or 新耐震. There is no badge, no filter, no warning.

You have to do the math yourself: if the build year is 1981 or earlier (or more precisely, if the construction permit was issued before June 1981), the property is 旧耐震.

Practical risks for buyers

• Structural safety — the building may not withstand a major earthquake. Japan's seismic activity makes this a real, ongoing risk, not a theoretical one.
• Mortgage financing — some Japanese banks refuse or limit loans on 旧耐震 properties. This also affects your exit: future buyers may face the same restriction.
• Home insurance — earthquake insurance premiums are higher, and some policies apply deductibles or coverage caps to 旧耐震 structures.
• Retrofit costs — seismic retrofit (耐震補強工事) typically costs ¥1–3M+ depending on the building. Some municipalities subsidize this, but it is not guaranteed.
• Resale value — 旧耐震 properties are harder to sell to Japanese buyers who understand the standard, and the gap in value versus 新耐震 equivalents continues to widen.

What to confirm before buying

1. Has a seismic diagnosis (耐震診断) been conducted? If yes, request the report.
2. Has seismic retrofit work (耐震補強工事) been completed? If yes, request documentation.
3. Does the property qualify for the municipality's retrofit subsidy (耐震改修補助金)?
4. Will the bank you plan to use lend on this property as-is?
5. Is earthquake insurance available at standard terms for this property?

Questions to ask the agent (Japanese)

Official source

The 1981 revision to Japan's Building Standards Act (建築基準法) is the legal basis for the new/old seismic standard distinction. The Ministry of Land, Infrastructure, Transport and Tourism (国土交通省) publishes guidance on seismic retrofitting: 「既存住宅の耐震診断・改修」 — available via the MLIT website. Municipal retrofit subsidy programs are managed locally; confirm with the relevant 役所 (city/ward office).

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