Kento-kunThis memo provides a clear summary of the laws frequently used in the design of new wooden houses and small-scale buildings.
Kento-kunI’ve got to study hard again today!
Today’s basic architectural design topic is Article 1 of Japan’s Building Standard Law.
Article 1 sets out the purpose of the law, and it states as follows.
(Purpose)
Article 1 The purpose of this Law is to establish minimum standards concerning the site, structure, equipment, and use of buildings, thereby protecting the life, health, and property of the people, and contributing to the promotion of the public welfare.
Source: Article 1 of Japan’s Building Standard Law
Kento-kunThe key point of Article 1 is the phrase “minimum standards.”
This means that when you construct or design a building, you are required to follow the standards set by this Law. At the same time, these standards represent only the minimum requirements.
As for these minimum standards, in the case of earthquakes, they generally mean that a building should suffer little or no damage during an earthquake of about shindo 5-upper, and that even in a very rare major earthquake of around shindo 6-upper to shindo 7, it should not collapse or cause life-threatening harm.
For reference, the JMA Seismic Intensity Scale Reference Table published by the Japan Meteorological Agency explains the characteristics of shindo 5-upper and higher as follows.
| Seismic Intensity | Human Perception / Behavior | Indoor Conditions | Outdoor Conditions |
|---|---|---|---|
| Shindo 5-upper | Most people find it difficult to walk without holding on to something and experience difficulty moving. | More dishes on shelves and books on bookshelves begin to fall. Televisions may fall from stands. Unsecured furniture may topple over. | Window glass may crack and fall. Unreinforced concrete-block walls may collapse. Poorly installed vending machines may fall over. Driving becomes difficult, and some cars may stop. |
| Shindo 6-lower | It becomes difficult to remain standing. | Most unsecured furniture moves, and some of it may topple over. Doors may become impossible to open. | Wall tiles and window glass may be damaged and fall. |
| Shindo 6-upper | It is impossible to remain standing, and movement is only possible by crawling. People may be thrown about by the shaking and may even be tossed. | Almost all unsecured furniture moves, and much of it topples over. | Many buildings experience falling wall tiles and broken or falling window glass. Most unreinforced concrete-block walls collapse. |
| Shindo 7 | Same as above. | Almost all unsecured furniture moves, topples over, or may even be thrown. | Even more buildings experience falling wall tiles and broken or falling window glass. Some reinforced concrete-block walls may also be damaged. |
Kento-kunSo maybe it is better not to design only to the minimum standard.
Kento-kunIf a house is designed only to the minimum standard, it may not collapse in the first major earthquake of around shindo 6-upper or shindo 7, but it could still collapse in a second earthquake. That is why, when designing a building in earthquake-prone Japan, it is better to exceed the minimum standard.
Kento-kunI see. In that case, I might aim for Seismic Grade 2 or 3, taking post-earthquake living conditions and continued usability into account.
Kento-kunSeismic grade is determined not by the Building Standard Law itself, but by a separate system called the Housing Performance Labeling System, and obtaining it is optional. Even so, it is widely used in Japan as a third-party framework for evaluating seismic performance. For reference, the performance of each seismic grade is shown in the table below.
| Seismic Grade | Performance Description |
|---|---|
| Seismic Grade １ | Meets the minimum standard under Japan’s Building Standard Law and is able to withstand seismic forces from very rare earthquakes (roughly once every several hundred years). |
| Seismic Grade ２ | Able to resist collapse or major failure under seismic forces 1.25 times greater than those assumed for Seismic Grade 1. |
| Seismic Grade ３ | Able to resist collapse or major failure under seismic forces 1.50 times greater than those assumed for Seismic Grade 1. |
Kento-kunThen I would probably aim for Seismic Grade 3 and add a vibration control system as well. That would help people who use the building feel more secure.
In this memo, I explained the purpose of Article 1 of Japan’s Building Standard Law. In modern architectural design, it is rare to design only to Seismic Grade 1, and it is common practice to design to a higher level. Manneko, the author of this blog, also designs buildings to Seismic Grade 2 or above.
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