One year has passed since Japan's Building Standards Act amendment (April 1, 2025) narrowed the "4-go exemption" for small houses. This article reviews the practical impact and remaining issues.
What Was 4-Go Tokurei?
Before the amendment, Article 6(1)(iv) of the Building Standards Act allowed small wooden two-story houses ("4-go buildings") to skip structural review during building confirmation — a relic from an era when paperwork review was thought sufficient for small structures.
Reform Rationale
- Designs by architects without structural specialization were going through unchecked
- This produced structurally weak housing in the market
- The 2011 Tohoku earthquake and 2016 Kumamoto earthquake exposed the failures
- Alignment with longer housing lifespans and energy efficiency mandates (effective April 2025 simultaneously)
Key Amendment Points
1. Narrowed scope of "4-go" buildings
| Category | Before | After (New 2-go / 3-go) |
|---|---|---|
| Wooden two-story houses | 4-go | New 2-go |
| Wooden single-story over 200m² | 4-go | New 2-go |
| Wooden single-story up to 200m² | 4-go | New 3-go (exemption preserved) |
2. Mandatory structural plan review
New 2-go buildings require specification rule review (wall quantity calculation, etc.) at confirmation stage.
3. Simultaneous energy efficiency mandate
The Housing Energy Conservation Act also took effect April 1, 2025, requiring new housing to meet energy efficiency standards. Energy calculation documents must accompany confirmation applications, increasing paperwork load.
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Housing Start Statistics
Per MLIT's Building Start Survey, wooden detached-house starts have declined 10-15% YoY since April 2025.
- FY2024 (through March 2025): pre-amendment rush, +8% YoY
- April 2025 onward: rebound dip, -12 to -15%
A classic "rush → rebound" pattern, with signs of bottoming out in spring 2026.
Plan Review Backlog
Particularly in major metropolitan areas (Tokyo, Osaka, Nagoya), plan review now takes 2-4 weeks longer.
| Region | Before | After |
|---|---|---|
| Tokyo 23 wards | 14 days | 35-42 days |
| Osaka City | 14 days | 30-35 days |
| Regional cities | 14 days | 21-28 days |
Structural Engineer Shortage
- Class 1 structural architects nationwide: approximately 12,000 — far below demand
- Wooden house structural calculation specialists: approximately 30,000 estimated
- Small contractors increasingly rely on outsourced structural design
Price Impact
- Confirmation application fees and structural calculation costs passed to housing prices
- Wooden detached house average: ¥300,000-800,000 added cost
- Large home builders: absorbed via in-house capability
- Small contractors: negotiating cost pass-through with customers
Buyer Protection Perspective
Positive Effects
- Stronger pre-review reduces structural quality issues post-completion
- Industry surveys show fewer reported structural problems
- Earthquake insurance discounts expanded for certified buildings
Negative Effects
- Housing prices up ¥300,000-800,000 average
- Construction periods extended 1-2 months
- Small contractor closures up 3.2% YoY (more pronounced regionally)
- Two-tier existing housing market (pre/post amendment)
Remaining Issues
- Existing non-conforming structures: handling of small wooden houses built before the amendment
- Structural engineer training: MLIT targets 1.5x increase by 2030 — long lead time limits short-term effect
- Regional manpower gaps: architect office closures plus municipal review office shortages
- Small contractor survival: regional supply capacity at risk
Implications for Real Estate Transactions
New construction purchase
- Verify confirmation completion: ensure structural review completed for post-amendment construction
- Obtain structural calculation documents: get originals from seller
- Energy performance evaluation: confirm Housing Energy Conservation Act compliance
- Construction delay risk: build margin into delivery timing
Existing home purchase
- Verify construction date: post-April 2025 means new standards
- Possible non-conforming status: pre-March 2025 may need structural evaluation
- Inspection: strongly recommend third-party home inspection
- Earthquake compliance certificate: needed for mortgage deduction and insurance discounts
Conclusion
One year post-amendment, the picture is mixed: short-term reduction in housing starts and longer review periods versus long-term improvement in structural safety. The buyer protection perspective is clearly positive. Real estate disputes, housing defects, and construction litigation now turn on whether construction predates or postdates the April 2025 reform — consult a real estate or construction-law attorney for fact-specific analysis.
