The Relationship Between Building Age and Earthquake Resistance in Rental Properties—Understanding the 1981 New Seismic Standard and How to Choose Safe Properties

On June 1, 1981 (Showa 56), the Building Standards Act was amended and the 'New Seismic Standard' was enacted. Following the 1978 Miyagi-Oki Earthquake (M7.4), this major legal reform significantly strengthened the seismic design standards for buildings.

Old Seismic Standard (buildings constructed before May 31, 1981) It was based on the standard that buildings would not collapse in medium-scale earthquakes of around seismic intensity 5. There was no clear standard for major earthquakes (seismic intensity 6-7), and many buildings built to the old standard suffered significant damage in the 1995 Great Hanshin-Awaji Earthquake.

New Seismic Standard (buildings constructed on or after June 1, 1981) 'Buildings shall not collapse or crumble even in major earthquakes of seismic intensity 6-7' is the standard, and design emphasizing building resilience (ductility) is required.

When selecting rental properties, whether a building 'received building permit approval on or after 1981' is the minimum standard for assessing safety. However, note that the 'building permit year' and 'completion year (building age)' may differ.

Earthquake Resistance That Cannot Be Judged by Building Age Alone

Even buildings that meet the new seismic standard may differ in earthquake resistance performance due to the following factors.

2000 Amendment (strengthened standards for wooden structures) Wooden buildings were strengthened under the 2000 Building Standards Act amendment with requirements for 'mandatory use of metal connectors at joints,' 'mandatory geotechnical surveys,' and 'strengthened wall balance regulations.' Wooden buildings built between 1981 and 2000 meet the new seismic standard, but may not match the level of those built to 2000 standards.

Quality control for reinforced concrete and steel-frame structures The quality of concrete placement and the precision of steel welds depend on the contractor's technical capability. If the building is not constructed according to the design plans that meet the new seismic standard, earthquake resistance performance may be insufficient.

Impact of soft ground Even if a building itself meets seismic standards, buildings constructed on soft ground with high liquefaction risk may be subject to differential settlement or tilting during earthquakes. This can be confirmed through the Ministry of Land, Infrastructure, Transport and Tourism's 'Real Estate Information Library' and hazard maps.

Key Points for Verifying Seismic Diagnostics and Retrofitting

Even buildings built to the old seismic standard can maintain a certain level of safety if seismic diagnostics and seismic retrofitting work have been completed.

Seismic diagnosis This is a survey that assesses a building's current earthquake resistance performance and evaluates it numerically. If the 'Is value (Seismic Index of Structures)' is 0.6 or higher, the building is considered to have adequate earthquake resistance.

Seismic retrofitting Based on the results of the seismic diagnosis, this work strengthens columns, walls, foundations, and other structural elements. In large apartment buildings, management associations sometimes fund these projects from reserve funds.

How to verify for rental properties

• •Ask the management company or real estate broker directly about whether seismic diagnosis and retrofitting have been performed
• •Check whether 'seismic retrofitting complete' stickers or certificates are posted near the building entrance or in the lobby
• •Refer to the local government's public 'seismic retrofitting history' records if available

Practical Checklist for Choosing Safe Rental Properties

Items to Confirm Before Viewing and Application

Basic building information

• •Confirm that the building permit year or completion year is on or after June 1981
• •For wooden structures, buildings completed in 2000 or later are preferable

Type of structure General order of earthquake resistance: Reinforced concrete ≧ steel-frame structures > wooden structures (2000 standard) > wooden structures (old standard)

Verify hazard maps Check flood, landslide, and liquefaction risks for the property location at the Ministry of Land, Infrastructure, Transport and Tourism's 'Real Estate Information Library' (https://www.reinfolib.mlit.go.jp).

Key points to check during viewings

• •Visually inspect for large cracks or tilting in the building's exterior
• •Check whether hallways and stairs are level (smooth door and window operation is a good indicator)
• •If an elevator is present, verify whether vibration control or seismic isolation equipment is installed

Important Considerations When Living in Properties Built to Old Seismic Standards

If you choose a property built to the old seismic standard (45+ years old) for cost reasons, consider the following points.

Action plan in case of earthquake

• •Identify your nearest evacuation shelter and evacuation route in advance
• •Implement thorough furniture stabilization measures (use tension rods and L-shaped brackets)
• •Maintain well-stocked emergency kits and supplies

Review fire insurance Earthquake insurance premiums for buildings built to the old seismic standard are higher than for properties meeting the new standard. Consider purchasing earthquake insurance to ensure coverage in case of disaster.

Trade-off between rent and safety While older seismic standard properties tend to have lower rents, it's important to make your choice with full awareness of the trade-off between cost and earthquake resistance risk.

Summary

While the 1981 New Seismic Standard is a critical benchmark for assessing earthquake resistance in rental properties, you should also consider building structure, soil conditions, construction quality, and whether retrofitting has been performed. When selecting a property, verify the hazard map, confirm the structure type and building age, and check whether seismic retrofitting has been completed. Choosing a safe living environment is just as important a decision criterion as initial costs and rent.

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