When considering investment in a used condominium or purchasing one for your own residence, evaluating seismic resistance is one of the most important decision criteria. It is essential to understand the difference between the new and old seismic standards, as well as the features of the three main earthquake countermeasure construction methods.
What is the difference between the new seismic standard and the old seismic standard?
Seismic standards are the criteria that define the level of earthquake resistance required when a building is designed. They underwent a major revision in 1981.
- Old seismic standard (before 1981)：The benchmark was that a building should withstand an earthquake of roughly upper 5 on the Japanese seismic intensity scale
- New seismic standard (1981 onward)：The benchmark is that a building should not collapse even in an earthquake of roughly upper 6 to 7 on the Japanese seismic intensity scale
The standards were strengthened in response to the damage caused by the 1978 Miyagi-Oki Earthquake. When buying a used condominium, always confirm whether the building confirmation date is on or after June 1, 1981.
What is the difference between seismic resistance, vibration control, and base isolation?
There are three main approaches to earthquake protection in buildings.
| Construction method | Principle | Features |
| Seismic resistance | Strengthen the building itself | Structural reinforcement and additional strengthening components |
| Vibration control | Absorb impact | Disperse shaking energy with damping devices |
| Base isolation | Block shaking | Install isolation devices between the ground and the building |
In general, base isolation is considered the most effective for seismic performance, but it also comes with higher cost.
What should you check when evaluating the seismic resistance of a used condominium?
These checkpoints are useful for both investment and residential decisions.
Check the management and maintenance condition
No matter how robust the structure is, deterioration will progress if maintenance is inadequate. Check the cleanliness of the property, its repair history, and whether a long-term repair plan is in place.
Check the building structure and construction method
Confirm which of the three methods, seismic resistance, vibration control, or base isolation, has been adopted. Also note that if the first floor uses a pilotis structure supported only by columns, extra caution is needed regarding seismic performance.
Check whether a seismic diagnosis has been conducted
For properties built under the old seismic standard, confirm whether a seismic diagnosis has been conducted and review the results. Properties that have already undergone seismic retrofitting work offer greater safety.
Frequently Asked Questions (FAQ)
Should you avoid buying properties built under the old seismic standard?
Not necessarily. If seismic retrofitting work has been carried out, safety can be improved. However, properties that have not undergone a seismic diagnosis carry higher risk and are generally better avoided.
What is a seismic grade?
Seismic grade is an indicator of earthquake resistance under Japan’s Housing Performance Indication System, with three levels from Grade 1 to Grade 3. Grade 1 corresponds to the Building Standards Act level, while Grade 3 provides 1.5 times that level of seismic resistance.
What should you check besides seismic resistance when buying a used condominium?
Check the condition of the plumbing, the contents of the long-term repair plan, the financial status of the management association, and the balance of the repair reserve fund.
