Planning a Renovation in Japan? What to Know About the 2025 Building Code Update
As of April 1, 2025, Japan’s Building Standards Act has undergone major revisions that will significantly impact both new constructions and renovation projects. These legal updates are part of a national push toward Japan’s 2050 carbon neutrality goals and reflect the government’s broader initiative to improve energy efficiency and safety in the building sector.
One of the most notable revisions is the end of the “Category 4 Special Exception,” which previously allowed small wooden homes to skip certain building reviews. But beyond that, the law now introduces stricter structural review rules, mandatory energy efficiency compliance, and updated fire safety guidelines—particularly for timber construction.
If you’re planning to renovate a traditional Japanese home (like a machiya or kominka), here’s what you need to know.
Why Was the Law Revised?
The main goal of the 2025 amendment is to reduce energy consumption in the building sector, which accounts for roughly 30% of Japan’s total energy use. The revised act promotes the use of sustainable building materials like wood, supports decarbonization, and updates outdated regulations to match modern construction practices. These changes aim to make buildings safer, more energy-efficient, and better aligned with long-term environmental goals.
Aside from the Revised Law, Here’s What to Expect:
Longer Approval Timelines for Building
ConfirmationAs of April 2025, the statutory review period for building confirmation has increased from “within 7 days” to “within 35 days.” Actual turnaround times may vary based on how busy reviewing agencies are, but delays are expected—especially during the first months of implementation. MLIT recommends early submission to avoid bottlenecks.
Rising Costs for Applications and Design
The increased review scope and added compliance checks have raised the complexity of architectural designs and applications. Architects are now responsible for submitting more documentation, which increases design timelines and costs. Combined with rising labor and material prices, overall construction budgets will likely increase.
Key Changes in the 2025 Building Standards Act
- End of the Category 4 Special Exception
Previously, small-scale wooden homes under 500 square meters were exempt from full structural and fire safety reviews. As of April 2025, that exception is gone. These buildings are now split into two categories: New Category 2 (two-story wooden buildings over 200 sqm) and New Category 3 (one-story wooden buildings under 200 sqm). Most of these structures must now go through standard building confirmation and inspections unless built in non-urban zones.
- Energy Efficiency Now Mandatory
All new construction must now comply with national energy-saving standards. This includes meeting BEI (primary energy consumption) targets and insulation requirements. For renovation projects, only the newly added or modified sections need to comply with energy efficiency rules.
- Simplified Structural Requirements for Timber Buildings
Timber buildings up to three stories or 16 meters in height can now be designed using simplified structural calculations. Second-class architects are now permitted to design such buildings. However, structures over 300 sqm must still go through structural verification (down from the previous 500 sqm threshold). New wall and pillar sizing rules also account for heavier modern features like solar panels and triple-glazed windows.
- Updated Fire Safety Regulations
Large wooden buildings over 3,000 sqm no longer have to fully cover timber frames with non-combustible materials. Architects can now use exposed timber under approved structural methods. For mid-rise buildings (5–9 floors), the requirement has been relaxed to only 90 minutes of fire resistance on the ground floor. These changes improve both safety and design flexibility.
- Revised Fireproofing for Mid-Rise Timber Buildings
In the past, fireproofing standards applied the same way to all buildings between 5 and 14 floors. Now, fire resistance requirements for timber structures in this range are adjusted, making mid-rise construction more viable and cost-effective.
Partial Exemptions for Older Non-Compliant Buildings
Buildings constructed before modern laws came into effect—often in narrow streets or with unique land constraints—may qualify for special exemptions. This change supports the reuse of older structures, encourages renovation, and helps preserve architectural heritage while still following essential safety practices.
Choosing the Right Contractor Matters More Than Ever
These legal changes mean that most renovation projects will now require building confirmation documents, structural safety reviews, and energy efficiency reports. Contractors unfamiliar with these new requirements may cause delays or even force project redesigns. Homeowners should now work with firms that either employ licensed architects or regularly collaborate with qualified professionals who can handle compliance.
How Heritage Homes Japan Is Prepared
Heritage Homes Japan is fully equipped to meet these updated regulations. Our team includes licensed architects, project managers, and compliance experts with experience in traditional home renovations such as machiya and kominka. We manage the necessary documentation, structural assessments, and approvals to keep your renovation smooth, legal, and future-ready.
Planning a Renovation in 2025 or Beyond?
Here’s what you should consider:
Start the planning process early to accommodate longer approval times.
Work with contractors who understand the updated law.
Budget realistically for additional steps like compliance checks and design verification.
Feel free to contact us for a consultation. We’ll guide you through what these legal changes mean for your specific project and how to move forward with confidence.