On 1 April 2025 two changes took effect together in Japan that reshaped how ordinary buildings are designed and reviewed. Energy conservation conformity became mandatory for essentially all new buildings, and the long-standing review exemption for small wooden houses, known as the 4-go exemption, was substantially narrowed. Individually each is significant. Together they mean many projects that used to pass through confirmation on light paperwork now require full structural and energy documentation.
How does building approval work in Japan?
New building work generally requires a building confirmation, kenchiku kakunin, before construction starts. The application is reviewed either by a local government building official or by a designated confirmation and inspection body, and the project is inspected during and on completion of the works. The governing legislation is the Building Standards Act and its Enforcement Order, alongside the Building Energy Efficiency Act for energy performance.
Change one: energy conservation conformity is now mandatory
Before April 2025, mandatory conformity with energy conservation standards applied to larger buildings, with smaller residential work subject to lighter obligations. From 1 April 2025, conformity applies to essentially all new buildings, residential and non-residential. In practice this means energy performance is now something a small house project must document and demonstrate, not merely consider.
The policy driver is decarbonisation. Buildings account for a large share of national energy consumption, and Japan has committed to carbon neutrality by 2050, so tightening the standard for the large volume of small residential construction is where the remaining gains sit.
Change two: the 4-go exemption has been narrowed
This is the change that has had the most effect on day-to-day practice. Under the previous framework, small wooden two-storey houses fell into the category commonly called 4-go, and the associated exemption allowed applicants to omit structural review documentation from the confirmation application. That exemption has been restructured.
| Category | Covers | Effect |
|---|---|---|
| New 2-go | Wooden two-storey buildings, and wooden single-storey buildings over 200 sqm | Exemption removed. Structural documentation must be submitted with the confirmation application. |
| New 3-go | Wooden single-storey buildings up to 200 sqm | A narrowed exemption is retained. |
The practical consequence is that the ordinary two-storey wooden house, the most common building type in Japanese residential construction, now goes through structural review at confirmation stage. Documentation that was previously optional, including wall quantity calculations and supporting structural material, has to be prepared and submitted, and energy performance documentation sits alongside it. Confirm the precise categories and thresholds that apply to your project with the reviewing body, since the detail sits in the Act and its Enforcement Order.
Who does this affect most?
Smaller residential practices and builders, disproportionately. A large commercial designer was already producing structural calculations and energy documentation as a matter of course. A designer of detached houses may not have been, and now must, on every project. That is a change in workload and in the skills required, not just a change in paperwork, and it arrived at the same time as the energy conformity obligation.
How do you check a Japanese project against the requirements?
The documents that govern a Japanese project are in Japanese, which is a real obstacle for international teams working on projects in Japan and for anyone reconciling a client standard written elsewhere. UptoCode works with the code you provide, in the language it is written in, so you can upload the relevant provisions alongside your drawings and BIM model and check the design against them, with each finding cited to the clause and the drawing or model element it came from.
It is worth being clear about the limits. UptoCode does not perform the building confirmation, and it does not replace the structural engineer or the reviewing body. It helps a team find gaps in the documentation before it goes for confirmation, which is exactly where the new obligations bite.
See our guide on checking drawings before submission, or how UptoCode reads BIM and IFC models. Create a free account and run a cited check with 65 free credits, no card required.
Last reviewed 28 July 2026. This article is general information, not compliance or legal advice. The Building Standards Act, its Enforcement Order, and the associated energy legislation govern the detail; confirm the requirements for your project with the reviewing body or a qualified professional in Japan.