Japan’s Disaster Risk Areas: What Article 39 Means Before You Buy or Rebuild

A Japanese “Disaster Risk Area” can restrict rebuilding, but the exact rule comes from the local ordinance and official designation map.

Current-law check: August 22, 2026 · For buyers planning to occupy, renovate, extend, rebuild or change the use of a property in Japan

“The property is in a 災害危険区域. Does that mean I cannot rebuild the house?”

Before you make the purchase conditional only on a general hazard-map result, obtain these three items:

1. The current official designation map or notice for the exact site—not just a national portal screenshot.
2. The ordinance and the site’s classification, including the provisions on use, floor height, structure, exceptions and transitional treatment.
3. A project-specific answer for the existing building and what you plan to do: continue using it, renovate, extend, rebuild, alter the land or change use.

About Yamaken. I am a Japan-licensed First-Class Architect, qualified building regulation conformity inspector and Real Estate Transaction Specialist. I spent more than ten years in national and local government, including building-control and urban-planning work. That experience is why I stop a property review when the map, ordinance and proposed work have not yet been connected. Full profile (Japanese).

My stopping rule: “It is in an Article 39 area” is not yet a usable conclusion. I need the boundary, the controlling article of the ordinance and the proposed building work on the same page.

My position as an architect: it should not be the default land choice

An Article 39 Disaster Risk Area is not merely a place where a map happens to show a hazard colour. It is an area that a local government has formally designated because the danger from tsunami, high tide, flooding or a similar event is serious enough to justify restrictions on building.

For that reason, my default professional position is that an Article 39 area is not a desirable place to acquire land. A route to technical compliance under the ordinance does not remove the underlying site hazard. If two reasonably comparable sites are available, I would normally choose the site outside the designation.

There can be exceptional reasons to continue investigating—a location that cannot be substituted, an existing use with a carefully verified evacuation strategy, or a project designed around the local conditions—but the burden of proof should be higher. The buyer should document why this site is still being considered, what alternatives were compared, which residual risks remain and who will bear the additional cost and limitation.

Article 39 delegates the practical rule to the locality

The Japanese term is 災害危険区域 (saigai kiken kuiki, “Disaster Risk Area” in the official translation database). Article 39 does two things. Paragraph 1 allows a local government to designate, by ordinance, an area with serious danger from tsunami, high tide, flooding and similar events. Paragraph 2 requires the same ordinance to set the disaster-prevention restrictions on building there, including any prohibition on constructing buildings used as housing.

The national Act therefore does not give every Article 39 area one nationwide setback, floor level or structural specification. You have to find the local instrument. The important words for a buyer are not only “Disaster Risk Area,” but also which local government, which ordinance, which mapped sub-area and which proposed work.

A hazard-map color is not the Article 39 designation

A flood, storm-surge or tsunami map may be part of the evidence that led to a designation, but the colored hazard layer and the legal boundary are not interchangeable. The source law, purpose, scenario, date and boundary method can differ. The ordinance may also divide the legal area into classes that do not match the depth bands on the hazard map.

MLIT’s National Land Numerical Information provides Disaster Risk Area data as dataset A48. It is useful for nationwide screening, but its published 2021 data warns that designations are revised, the latest status may not be reflected, and the geometry is approximate. The Real Estate Information Library currently identifies that same 2021 national dataset as its source for the Disaster Risk Area layer.

I therefore use it in two stages. Stage 1: use A48 in QGIS or the Real Estate Information Library to identify a possible Article 39 overlap. Stage 2: move to the responsible municipality or prefecture and obtain the current designation map, notice and ordinance. The national layer is an efficient way to find the question; it is not the document that closes it.

See the A48 areas on a QGIS-built screening map

The map below is built from the same MLIT A48 files in QGIS. Choose a prefecture, zoom in and select an outlined area to read the dataset attributes. I have deliberately omitted records whose source terms prohibit commercial use or redistribution, mark the data non-public, or do not give a clear matching permission. An apparent gap can therefore mean an omitted record, missing geometry, a later designation or simply that the FY2021 dataset did not capture the area. It must never be read as proof that no Article 39 designation exists.

Three official examples—and three different answers

Nagoya: four classes and project-specific height rules

Nagoya’s 臨海部防災区域 (rinkai-bu bōsai kuiki, coastal disaster prevention area) was created after the 1959 Ise Bay Typhoon. The city’s current official page divides the area into four classes. Its summary shows different first-floor elevation and structural requirements by class: for example, the first class uses a Nagoya Port datum of N.P. +4 metres for the first-floor level and prohibits wooden construction, while the second through fourth classes use other combinations and exceptions. In a specifically designated strip within the first class, buildings with habitable rooms, hospitals and certain welfare facilities are prohibited unless the stated exception is met.

This is not a rule you can apply from an ordinary flood-depth legend. You need the official class, the correct vertical datum, the building use and the detailed ordinance. Nagoya also tells readers to confirm the specially designated 50-metre strip using its official coastal-area map or with the Building Guidance Division.

Nagasaki Prefecture: another designation system, another structure test

Nagasaki Prefecture’s official guidance links its Article 39 designation partly to designated steep-slope failure danger areas, but adds an important date qualification: some areas designated before October 15, 1982 are not included. It also identifies separately designated areas, exclusions and a building restriction for housing, hotels, hospitals, schools and assembly buildings. The current ordinance summary focuses on reinforced-concrete or equivalent principal structural parts and safety against the specified event, subject to listed exceptions.

A buyer who checks only the present-day steep-slope map can therefore miss the legal question. The designation date, the Article 39 ordinance, the landslide special warning area and any protective works need to be separated.

Yokohama: an official page currently reports no designation

Yokohama’s official Building Standards Act area page currently states that no Article 39 Disaster Risk Areas are designated in the city. That does not mean “no disaster risk” and it does not erase other statutory areas or site problems. It answers one narrow question: the city’s current Article 39 designation status.

These three examples are the point of the article. The phrase “Disaster Risk Area” is national, but the legal work happens through a local designation and ordinance. A nationwide yes/no label is too coarse for a purchase decision.

Existing house, renovation and rebuilding are not the same question

Article 39 and the local ordinance regulate building, but the consequence for an existing property depends on facts that a map cannot supply. When was the area designated? When was the building constructed or approved? Has it been extended or altered? Does the ordinance contain an exception or transitional rule? Does your work amount to construction, extension, major repair, major remodelling or a change of use under the applicable provisions?

An existing house may be usable today yet unable to be rebuilt in the same form. Another building may be capable of a compliant replacement, but only after raising the floor, changing the structure or documenting a protective measure. Do not turn either possibility into a general rule. Compare the current ordinance with the approval history and the proposed drawings.

The document trail I would build before contract

1. Fix the site. Use the address, cadastral information and a survey or site plan. If a line touches the land, ask which official record controls and how the authority resolves boundary questions.
2. Obtain the current designation. Save the official map, notice or certificate, its publication or revision date, scale, legend and local class. Do not substitute a broker’s screenshot.
3. Read the operative ordinance. Mark the provisions for designation, affected building uses, prohibited work, floor level, structure, site measures, exceptions, approvals and transitional rules.
4. Build the property history. Request the building confirmation and inspection certificates, approved drawings, development or retaining-wall records, alteration history and any prior consultation about the designation.
5. Describe the project in plain facts. Existing use, proposed use, demolition, extension area, structural work, floor level, number of storeys and any earthwork should be clear before you ask the authority.
6. Get a written record of the answer. Record the office, date, official spoken to, documents reviewed, conclusion, conditions and unresolved items. A verbal “probably fine” is not a durable due-diligence result.

Four questions for the building-control office

• Does the latest Article 39 designation cover all or part of this site, and which class applies? Ask for the controlling map, notice and reference date.
• Which ordinance provisions apply to this building use and proposed work? Name the work instead of asking only whether “building is possible.”
• How is the boundary or required elevation confirmed? Ask whether a survey, datum conversion, certificate or separate department is required.
• Which issues are outside this office’s answer? Identify separate development-permission, landslide, river, retaining-wall, road, planning and site-investigation checks.

How to write the due-diligence result

Avoid “safe,” “legal” or “rebuildable” unless the full decision is actually within scope and supported. Use a narrower result:

• No applicable Article 39 designation confirmed in the public sources reviewed — name the authority, source and date, and keep other hazards separate.
• Article 39 designation and a condition confirmed — name the local class, ordinance article, affected action and project consequence.
• Pre-contract or pre-design consultation recommended — state the disputed boundary, missing elevation, uncertain exception or incomplete project description.
• Cannot be determined from public information alone — name the missing map, building record, survey, approved drawing or authority interpretation.

Then connect the result to the contract: a document-production condition, satisfactory authority consultation, design feasibility review, survey, price adjustment or a decision not to proceed. For land acquisition, my starting recommendation is normally to look for a suitable site outside the Article 39 designation. Continuing with a designated site should be an evidence-based exception, not the result of treating legal buildability as proof that the location is a desirable choice.