Building confirmation / Kominka renovation in Toyama
Does a kominka renovation need a building confirmation application?
Since April 2025, a two-storey wooden kominka needs building confirmation if you repair more than half of any one kind of part: posts, walls, floors, roof, stairs and so on. A single-storey house of 200 ㎡ or less still does not need it, as before.
Since April 2025, a two-storey wooden kominka needs building confirmation if you repair more than half of any one kind of part: posts, walls, floors, roof, stairs and so on. A single-storey house of 200 ㎡ or less still does not need it, as before.
Even a single-storey house needs building confirmation, like a two-storey one, if its total floor area is over 200 ㎡.
Replacing only roof tiles, re-covering only the surface of the outer wall, and replacing a kitchen or bath do not need an application.
Even with major repair or major remodelling, there is no duty to meet the energy-efficiency standard.
As a builder with a second-class architect on staff, we take care of everything from the application to the work and the completion inspection.
When you buy a kominka and renovate it, the procedure changed in April 2025. For the same work, whether you need building confirmation (a procedure where the local authority or a review body checks your drawings before the work) depends on whether the house has two storeys or one, and whether it is over 200 ㎡. This page explains that line using only MLIT materials and the text of the law.
What changed: the "Category 4" exemption was narrowed
A law promulgated in June 2022 (Act No. 69 of Reiwa 4) revised which buildings need building confirmation. It applies to work started in April 2025 or later.
Until then, wooden two-storey houses and wooden single-storey houses were called "Category 4 buildings". Category 4 buildings did not need building confirmation even for large-scale renovation. If an architect designed them, part of the structural review was also skipped. This is the "Category 4" exemption (a rule that skipped part of the review for small wooden houses).
After the revision, they fall into two groups.
New Category 2 buildings. These are wooden two-storey houses and wooden single-storey houses with a total floor area (the floor areas of all storeys added together) over 200 ㎡. In any area, they need building confirmation and inspection not only for new construction but also for major repair and major remodelling. They are also outside the scheme that skipped part of the review
New Category 3 buildings. These are wooden single-storey houses with a total floor area of 200 ㎡ or less. Major repair and major remodelling still do not need building confirmation, as before
In the text of the law, a building with two or more storeys or a total floor area over 200 ㎡ is "item 2". This applies regardless of structure, not only to wooden buildings. Before the revision, wooden two-storey houses outside city planning areas (areas covered by town-planning rules) were basically not subject to building confirmation. Now, a house outside such an area needs building confirmation if it is a new Category 2 building.
Work that needs an application, and work that does not
The fork between needed and not needed. Needed only when you repair more than half of the principal parts of a new Category 2 house
Building confirmation is needed when you do "major repair" or "major remodelling" on a new Category 2 house. The Building Standards Act defines them as follows. Major repair is "repair of more than half of one or more kinds of principal structural parts of a building." Major remodelling is "remodelling of more than half of one or more kinds of principal structural parts of a building." In short, it is work that repairs or rebuilds more than half of any one kind of part that forms the frame of the house.
The law defines principal structural parts as: "walls, posts, floors, beams, roof or stairs, excluding partition walls, intermediate posts, attached posts, raised floors, the lowest floor, revolving-stage floors, small beams, eaves, local small stairs, outdoor stairs and similar parts that are not structurally important to the building." In short, they are the walls, posts, floors, beams, roof and stairs that hold up the house. The ground-floor floor and partition walls that carry no load are not included.
How to count "more than half" is set for each kind of part.
Walls are counted by the share of the total wall area that you repair
Posts and beams are counted by the share of the total number that you repair. Small beams and diagonal corner braces (hiuchi braces) are not included
Floors and roofs are counted by the share of the area seen from directly above that you repair
Stairs are counted by the number of stairs on that floor. If the house has only one staircase, replacing it counts
MLIT says the following work is not major repair or major remodelling.
Replacing only the surface material of the roof (tiles and the like). The same applies when changing tiles to a metal roof. Laying a new roof over the existing roof is not covered either
Re-covering only the surface material of the outer wall. Adding insulation from inside the outer wall. Laying a new finish over the existing outer wall
Replacing only the surface material of a floor, or laying a new covering over it
Repairing only some of the steps of a staircase
Replacing a kitchen, toilet, bath or other plumbing fixtures. Installing handrails or slopes
On the other hand, if you replace every part that forms the roof, down to the rafters (the slim timbers that support the roof boards from below), and the area is more than half of the roof seen from directly above, it counts. For outer walls too, if replacing the surface material ends up replacing every part that forms the wall, and the area is more than half, it counts. Seismic reinforcement (work that makes the house stronger against earthquakes) is counted the same way.
Even when no application is needed, the house after the work must still meet the Building Standards Act. Also, for large-scale renovation of a house with a total floor area over 100 ㎡, an architect must do the design and supervise the work (an architect checks that the work follows the drawings).
Doing the work without an application carries penalties. The building owner (the person who orders the work) who did not apply, and the contractor who did the work without receiving a certificate of confirmation (a document showing the review was passed), face imprisonment of up to 1 year or a fine of up to ¥1 million.
Where does a Toyama Azumadachi house fall?
Azumadachi is a gabled, gable-end-entry house style that spread in western Toyama Prefecture. Its front shows a large triangular gable end (the triangular wall at the end of the roof). Whether such a house is new Category 2 or new Category 3 depends on two things.
Does it have a second floor? If so, it is new Category 2
Is the total floor area over 200 ㎡? Even if single-storey, over 200 ㎡ makes it new Category 2
Only single-storey houses that meet neither condition are new Category 3. Total floor area is the floor areas of all storeys added together. We decide after measuring on site.
For a kominka that is new Category 2, work such as replacing half or more of the posts or rebuilding the roof from the base layer needs an application. So it is important to decide, before you buy, how far you will repair and whether an application is needed.
The energy-efficiency standard is not a duty for renovations
The same law revision created a duty, from April 2025, for in principle all new houses to meet the energy-efficiency standard (the national standard for insulation and similar performance).
On the other hand, MLIT's Q&A collection says that renovations, meaning repairs and rebuilds, are outside the duty, and so is major repair and major remodelling. When you renovate a kominka, there is no duty to bring the whole house up to the energy-efficiency standard.
An extension (adding rooms) is treated differently. If the floor area of the extension is over 10 ㎡ and the house after the extension is new Category 2 or similar, only the extended part must meet the energy-efficiency standard.
Even without a duty, winter cold directly affects how comfortable the house is. Adding insulation from inside the outer wall is not major repair or major remodelling. How insulation work proceeds is in Insulation for kominka.
How are kominka that do not meet today's standards treated?
In old houses, the law may have changed after they were built, so some parts do not meet today's standards. This is called an existing non-conforming building (it met the law when built, but no longer meets today's standards after later amendments). The new rules are not applied to existing non-conforming parts.
However, when you extend a house or do major repair or major remodelling, you are in principle required to meet the current rules. This is called retroactive application (applying rules made later to an old house). Bringing the whole house up to today's standards can be too heavy a burden. So the law sets a relaxation that lets a house stay non-conforming under certain conditions (Building Standards Act Article 86-7, Enforcement Order Article 137-12).
MLIT's materials give the following examples for major repair or major remodelling of a two-storey wooden detached house.
Structural strength. If the work does not make the structure less safe, for example by not changing to a heavier roof, the house may stay non-conforming. Even if the foundation does not meet today's standards, you do not need to fix it as long as outer wall or roof work does not make things less safe
Rules on building size and height relative to the site. The house may stay non-conforming
Rules on rooms, equipment and stairs in parts not under major repair or major remodelling. The house may stay non-conforming
The relationship between the site and the road. If the use does not change in a way that adds users, and the authority recognises no problem, the house may stay non-conforming
On the other hand, if the work makes the structure less safe, the work must meet today's standards. This relaxation also applies only to existing non-conforming parts. It does not apply to parts that break the law. We inspect the house before the work and decide which parts fall where. How to repair damaged posts and sills is in Seismic reinforcement for kominka.
The application process, and how to think about days and cost
We (Hokuriku Homes, Nakamura Komuten Co., Ltd.) are a builder with a second-class architect on staff and a construction licence. For work that needs an application, we handle everything in-house, from design and application to the work and the completion inspection. The steps are as follows.
On-site survey. We check whether there is a second floor, the total floor area and the scope of repair
Survey of the current house. We check whether the house meets the law today. A certificate of inspection (a document showing the house passed the inspection after the work) makes this check simple
Design and application documents. Even for major repair or major remodelling, you basically need the same set of drawings as for new construction
Application. It goes to the building official (the officer at the city, town or prefecture who handles building confirmation) or to a private review body designated by the national government or prefecture
We start the work after receiving the certificate of confirmation
When the work ends, apply for the completion inspection within 4 days. The inspection takes place within 7 days of acceptance, and if you pass, a certificate of inspection is issued
When the application goes to a building official, the law says a new Category 2 house must be reviewed within 35 days of the day it is accepted.
Cost depends on the amount of drawings and the effort of surveying the current house. For a house with no drawings, the survey takes more effort. Costs differ from house to house, so we do not list them on this page. After the on-site survey, we include the application cost in the written quote for the work and tell you in writing.
Effect on the schedule
Work that needs an application cannot start until the certificate of confirmation is received. The survey of the current house, preparing the application documents and the review days are added before the work.
Take care when you change the plan during the work, too. If you change a confirmed plan, you need confirmation again, except for minor changes. If rotten sills or base material are found during the work and the area to be repaired exceeds half, we stop the work and file the application. That is why it is important to inspect everything before the work, including under the floor and in the attic.
If I only replace roof tiles with a metal roof, do I need a building confirmation application?＋−
No. MLIT says that changing only the surface material of a roof is not a major repair or major remodelling. Laying a new roof over the existing one is treated the same way. However, if you replace every part that forms the roof, down to the rafters (the slim timbers that support the roof boards from below), and the area is more than half of the roof seen from directly above, you need a building confirmation application.
What happens if rotten sills or base material are found during the work?＋−
If the area to be repaired turns out to be more than half, we stop the work and file the application. MLIT's Q&A collection says the same. To avoid stopping mid-work, we inspect everything before the work, including under the floor and in the attic, and decide the scope first.
My old house has no certificate of inspection. Can I still apply?＋−
You need to check whether the house meets the law today. A certificate of inspection makes this check simple. Without one, we inspect the house following MLIT's "Guidelines for Surveying the Current Condition of Existing Buildings" and prepare the application documents from the results.
If my kominka is single-storey, do I need no procedure at all?＋−
If the house is single-storey and its total floor area is 200 ㎡ or less, building confirmation is not needed even for major repair or major remodelling. A single-storey house over 200 ㎡ does need it. Adding rooms (an extension) is treated separately. Also, even when confirmation is not needed, the house after the work must still meet the Building Standards Act.
Must a renovation bring the house up to the energy-efficiency standard?＋−
No. Renovations that include major repair or major remodelling have no duty to meet the energy-efficiency standard. The duty applies to new buildings, extensions and rebuilds, and for extensions and rebuilds only to that part. Still, insulation that eases winter cold affects comfort and heating bills, so we recommend including it in your plan.
This page is a general explanation of the system. It is based on MLIT materials as of 2 October 2026 and the text of the Building Standards Act and its Enforcement Order. Whether your own work needs an application is decided by looking at the drawings and the site and consulting the review office. MLIT also advises consulting the review office when you cannot decide.