Short answer: a house whose building permit (建築確認) was issued before 1 June 1981 was designed to the "old seismic standard" (旧耐震基準), which aimed only at not collapsing in a moderate quake. Houses permitted after that date follow the "new standard" (新耐震), and wooden houses permitted after June 2000 follow a further tightened standard. A pre-1981 akiya is not automatically unsafe, but you should assume it needs a seismic diagnosis (¥100,000–200,000, often subsidised) and possibly a retrofit (commonly ¥1,000,000–2,000,000 for a small wooden house) — and that lenders, tax breaks and insurers will treat it differently.
The Building Standards Act enforcement order was amended after the 1978 Miyagi earthquake. The new standard (新耐震基準) requires a building to suffer little damage in a "medium" earthquake (roughly JMA intensity 5) and not collapse in a "large" one (roughly intensity 6-upper to 7). The old standard only addressed the medium case explicitly. The difference showed clearly in the 1995 Kobe earthquake, where a large majority of collapsed buildings were pre-1981.
A second change matters for wooden houses: from June 2000 the standard was tightened again (the "2000 standard"), adding requirements for foundation design to the ground, balanced placement of shear walls, and metal connectors at joints. Houses permitted between 1981 and 2000 are "new standard" but may still lack these details.
| Building-confirmation date | Standard | What it means in practice |
|---|---|---|
| Before 1 June 1981 | 旧耐震 (old) | Assume diagnosis and likely retrofit; lenders and tax rules treat it separately |
| 1 June 1981 – 31 May 2000 | 新耐震 (new), pre-2000 | Generally sound in design; wooden houses may lack connectors and balanced walls |
| From 1 June 2000 | 2000 standard | Current-style design for wood; fewest surprises |
Source: MLIT, 住宅・建築物の耐震化について; Building Standards Act enforcement order as amended 1981 and 2000.
The standard is fixed by the date the building confirmation (建築確認) was issued, not the date the house was finished or registered. A house registered in early 1982 may have been permitted in 1980 and therefore be old-standard. Listings usually show the completion or registration year (築年月). To be sure:
Note also that many rural houses were built without any confirmation at all (unconfirmed structures were common in areas outside city-planning zones), in which case there is no date to check and the house is treated as old-standard for all practical purposes.
A seismic diagnosis (耐震診断) by an architect trained in the standard method produces a score, the 上部構造評点 (Iw), for a wooden house:
| Score (Iw) | Assessment |
|---|---|
| 1.5 or more | Will not collapse |
| 1.0 – 1.5 | Unlikely to collapse |
| 0.7 – 1.0 | Some possibility of collapse |
| Below 0.7 | High possibility of collapse |
Most municipalities subsidise or fully fund the diagnosis for pre-1981 wooden houses (typical owner cost after subsidy: ¥0–50,000; unsubsidised ¥100,000–200,000). Some towns require the applicant to be the owner-occupier, so buy first, then apply — or ask the seller to apply now. The diagnosis report also lists the specific weaknesses, which becomes the retrofit plan.
Costs depend on the score, the size of the house and how much interior finish must be removed. Ranges reported by the Japan Building Disaster Prevention Association and municipal subsidy programmes for a typical single-storey to two-storey wooden house:
| Work | Typical cost | What it does |
|---|---|---|
| Adding structural plywood / bracing to walls | ¥100,000–300,000 per wall section | Raises shear-wall capacity; the core of most retrofits |
| Metal connectors at column–beam joints | Included in wall work; ¥5,000–20,000 per joint | Prevents columns pulling out (the 2000-standard detail) |
| Foundation repair or added reinforcement | ¥500,000–1,500,000+ | Needed when the foundation is unreinforced stone or cracked concrete |
| Roof lightening (tile to metal) | ¥800,000–2,000,000 | Reduces mass at the top; often combined with a needed re-roof |
| Whole-house retrofit to Iw ≥ 1.0 | ¥1,000,000–2,500,000 is a common range; more for large or badly damaged houses | Municipal subsidies of several hundred thousand to over ¥1,000,000 are common |
Cheaper partial options exist: a "safe room" (耐震シェルター) or a reinforced bedroom frame for ¥250,000–600,000 protects occupants without bringing the whole house to standard, and some towns subsidise these too.
| Item | Low | High |
|---|---|---|
| Purchase price | ¥2,000,000 | ¥2,000,000 |
| Acquisition costs (agent fee, taxes, registration) | ¥250,000 | ¥400,000 |
| Seismic diagnosis | ¥0 (subsidised) | ¥200,000 |
| Retrofit to Iw ≥ 1.0 (after typical subsidy) | ¥500,000 | ¥2,000,000 |
| Roof / water / termite repairs found during diagnosis | ¥300,000 | ¥2,000,000 |
| Total to a safe, habitable house | ≈ ¥3,000,000 | ≈ ¥6,600,000 |
The purchase price is often the smallest number. Sellers know this; the listing price already reflects that a buyer must spend on the structure.
| Japanese | English |
|---|---|
| 建築確認の年月日を教えてください。確認済証か検査済証はありますか。 | What is the building-confirmation date? Is there a confirmation or completion certificate? |
| 耐震診断を受けたことはありますか。あれば評点を教えてください。 | Has a seismic diagnosis been done? If so, what was the score? |
| 市の耐震診断・改修の補助金は、購入後の所有者でも使えますか。 | Can a new owner use the town's diagnosis and retrofit subsidies? |
| 基礎は鉄筋コンクリートですか、無筋または石ですか。 | Is the foundation reinforced concrete, unreinforced, or stone? |
| 屋根材は何ですか（瓦・スレート・金属）。 | What is the roof material (tile, slate, metal)? |
No. Many are heavily built with plenty of walls and score above 1.0 on diagnosis. The point is that you do not know until it is measured, and the cost of finding out is small.
Legally yes; there is no occupancy ban on old-standard houses. Owners of houses with very low scores are advised to sleep in a reinforced room or on the ground floor near an exit until work is done.
It increases the buyer pool (loans and tax breaks become available) more than the price. A compliance certificate is a selling point; keep the diagnosis and construction records.
Surviving a distant or moderate shaking proves little about a nearby strong quake. Past earthquakes can also have loosened joints and cracked foundations, which is one more reason to diagnose rather than assume.
The report reads the completion or registration year from the listing and flags anything before 1982 as CAUTION with the questions above. It cannot see the confirmation date if the listing omits it, so the certificate check is on you.
Have a specific listing in mind? Get the official zoning, hazard and transaction data for that exact lot — plus the questions to send the agent — in one PDF.
Get a $49 risk report Free 12-point checklistThis guide is general information based on public sources cited above. It is not legal, tax, or real-estate brokerage advice. Confirm every item for a specific property with the agent, the municipality, and licensed professionals.