Changes in the Building Standards Act 2025: Abolition of the Four-Number Exception


In 2025, a significant amendment to the Building Standards Act will take place, marking the abolition of the “four-number exception.” This exception previously allowed small-scale buildings, such as wooden houses and small commercial facilities, to bypass the confirmation application process. The abolition aims to enhance the safety and quality of all buildings by ensuring that every construction project undergoes strict review and inspection.

Case Study: Building a Wooden House

Current Scenario

Mr. Sato planned to build a two-story wooden house with a total floor area of 450 square meters in the suburbs of Tokyo. Under the four-number exception, he did not need to apply for confirmation. This allowed him to prepare the design plans and start construction quickly.


From 2025 onwards, if Mr. Sato wants to build the same house, he will need to submit design documents and go through a confirmation application process. Additionally, inspections will be required during the construction phase.

  • Benefits: Ensures the safety and compliance of the building design.
  • Challenges: The increased procedures could delay the start of construction.


Q: How will the abolition of the four-number exception affect construction costs?

A: The increase in construction costs will mainly stem from the additional procedures and inspections required. The exact increase will depend on the building’s size and location, but generally, initial costs are expected to rise slightly. However, this will lead to improved safety and quality of buildings, potentially reducing repair and maintenance costs in the long run.

The abolition of the four-number exception in the Building Standards Act in 2025 is a crucial step toward improving the safety and quality of buildings. By requiring all buildings to undergo confirmation applications and inspections, the amendment ensures compliance with safety regulations. This change, while requiring adaptation from the construction industry and homeowners, ultimately aims to provide safer, more reliable buildings.