Release of Seismic Simulation Results Complying with the April 2025 Building Standards Act Revision
In response to the April 2025 revision of the Building Standards Act, the Seismic Housing 100% Executive Committee has released results from seismic simulations using "wallstat." The simulations confirmed the safety of "Seismic Grade 3" under the new standards, validating the revised criteria designed to account for increased building weight due to energy efficiency measures.
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- 📰 Published: April 2, 2026 at 22:00
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The Seismic Housing 100% Executive Committee (Location: Chiyoda-ku, Tokyo) has released a report summarizing the results of seismic simulations conducted using the wooden house collapse analysis software "wallstat" (pronounced "wallstat"), in response to the revision of the Building Standards Act (review of wall quantity standards, etc.) which came into effect in April 2025.
This verification analyzed the differences in safety between the new standards (2025 standards) and the old standards (2000 standards), and between calculation methods, using an actual damaged property (Y Residence) from the Kumamoto Earthquake as a model.
* The seismic resistance factor (wall multiplier) used in this verification is uniformly set at 2.5 times.
■ Background: Increased building weight due to energy efficiency and legal revisions
The law revision in April 2025 revised the standards for calculating the required wall quantities according to actual conditions, driven by the increasing weight of buildings due to energy efficiency.
In response, our committee conducted detailed simulations to visualize the impact of the new standards on actual seismic resistance.
■ Conclusion: It was confirmed that Seismic Grade 3 does not collapse even by wall quantity calculation.
■ Main Verification Results
1. Increase in Required Wall Quantity due to Legal Revision
Comparison of Required Wall Ratio under Building Standards Act
For the old standards (2000 standards), the "lightweight roof" was used, while for the current standards (2025 standards), the wall quantity factor was calculated using the "New Wall Quantity Table Calculation Tool (Multi-function Version)". Compared to the old standards, the current standards showed an average increase of 1.41 times.
Comparison of Required Wall Ratio under Housing Quality Assurance Act (Hin-kaku-ho)
Comparing the old standards (2000 standards) and the current standards (2025 standards) under the Housing Quality Assurance Act specifications, the required wall ratio increased by an average of 1.12 times: 1.12 times for Seismic Grade 1 (30.5 ÷ 27.2), 1.13 times for Seismic Grade 2 (38.5 ÷ 34), and 1.12 times for Seismic Grade 3 (46 ÷ 41.1).
2. Safety of "Seismic Grade 3"
As a result of simulations using the seismic waves from the Kumamoto Earthquake on a model house designed according to the new standards, it was demonstrated that buildings with "Seismic Grade 3" do not collapse or suffer major damage.
Simulation Video of Wall Quantity Standard Revision with wallstat
Comparison of Existing Wall Quantity under Building Standards Act
It should be noted that there is a difference between the existing wall quantity under the Building Standards Act and the existing wall quantity for wall quantity calculation under Seismic Grade 1 of the Housing Quality Assurance Act in the verification results. This is because, in the calculation of required wall quantity, the floor area for wall quantity calculation under the Housing Performance Indication System is the floor area stipulated by the Building Standards Act, plus 40% of the area of the overhang on the second floor, the entrance porch area, and the balcony area on the first floor, and the area of the atrium on the second floor.
Calculation of Floor Area for Wall Quantity Calculation under the Housing Performance Indication System
3. Superiority of "Allowable Stress Calculation"
Even with the same seismic grade, it was observed that the "allowable stress calculation," which is more detailed, tends to result in a larger actual wall quantity (existing wall quantity) compared to the simpler "wall quantity calculation." The "allowable stress calculation" strictly considers factors such as the reduction of load-bearing walls on beams and twist correction, leading to a safer design, which suggests its superiority in ensuring building safety.
Load-Bearing Wall Arrangement in Structural Calculation
■ Future Outlook
Our committee will continue to verify whether the current standards are sufficient for major earthquakes that are anticipated to occur in the future, and will promote the importance of structural calculations (allowable stress calculation) for the widespread adoption of safer and more secure wooden houses.
Detailed simulation videos and the full report can be viewed at the following URL:
https://www.taishin100.or.jp/100standards/report/5021
---
**[Contact Information for this Matter]**
Secretariat, Seismic Housing 100% Executive Committee
Address: 7F, Akasaka Eight One Building, 2-13-5 Nagata-cho, Chiyoda-ku, Tokyo 100-0014
URL: https://www.taishin100.or.jp/
Keywords: Architecture, Law Revision, Wall Quantity Regulations, Wall Quantity Calculation, Allowable Stress, Living, Seismic Resistance, Seismic Housing, Earthquake, Home
This verification analyzed the differences in safety between the new standards (2025 standards) and the old standards (2000 standards), and between calculation methods, using an actual damaged property (Y Residence) from the Kumamoto Earthquake as a model.
* The seismic resistance factor (wall multiplier) used in this verification is uniformly set at 2.5 times.
■ Background: Increased building weight due to energy efficiency and legal revisions
The law revision in April 2025 revised the standards for calculating the required wall quantities according to actual conditions, driven by the increasing weight of buildings due to energy efficiency.
In response, our committee conducted detailed simulations to visualize the impact of the new standards on actual seismic resistance.
■ Conclusion: It was confirmed that Seismic Grade 3 does not collapse even by wall quantity calculation.
■ Main Verification Results
1. Increase in Required Wall Quantity due to Legal Revision
Comparison of Required Wall Ratio under Building Standards Act
For the old standards (2000 standards), the "lightweight roof" was used, while for the current standards (2025 standards), the wall quantity factor was calculated using the "New Wall Quantity Table Calculation Tool (Multi-function Version)". Compared to the old standards, the current standards showed an average increase of 1.41 times.
Comparison of Required Wall Ratio under Housing Quality Assurance Act (Hin-kaku-ho)
Comparing the old standards (2000 standards) and the current standards (2025 standards) under the Housing Quality Assurance Act specifications, the required wall ratio increased by an average of 1.12 times: 1.12 times for Seismic Grade 1 (30.5 ÷ 27.2), 1.13 times for Seismic Grade 2 (38.5 ÷ 34), and 1.12 times for Seismic Grade 3 (46 ÷ 41.1).
2. Safety of "Seismic Grade 3"
As a result of simulations using the seismic waves from the Kumamoto Earthquake on a model house designed according to the new standards, it was demonstrated that buildings with "Seismic Grade 3" do not collapse or suffer major damage.
Simulation Video of Wall Quantity Standard Revision with wallstat
Comparison of Existing Wall Quantity under Building Standards Act
It should be noted that there is a difference between the existing wall quantity under the Building Standards Act and the existing wall quantity for wall quantity calculation under Seismic Grade 1 of the Housing Quality Assurance Act in the verification results. This is because, in the calculation of required wall quantity, the floor area for wall quantity calculation under the Housing Performance Indication System is the floor area stipulated by the Building Standards Act, plus 40% of the area of the overhang on the second floor, the entrance porch area, and the balcony area on the first floor, and the area of the atrium on the second floor.
Calculation of Floor Area for Wall Quantity Calculation under the Housing Performance Indication System
3. Superiority of "Allowable Stress Calculation"
Even with the same seismic grade, it was observed that the "allowable stress calculation," which is more detailed, tends to result in a larger actual wall quantity (existing wall quantity) compared to the simpler "wall quantity calculation." The "allowable stress calculation" strictly considers factors such as the reduction of load-bearing walls on beams and twist correction, leading to a safer design, which suggests its superiority in ensuring building safety.
Load-Bearing Wall Arrangement in Structural Calculation
■ Future Outlook
Our committee will continue to verify whether the current standards are sufficient for major earthquakes that are anticipated to occur in the future, and will promote the importance of structural calculations (allowable stress calculation) for the widespread adoption of safer and more secure wooden houses.
Detailed simulation videos and the full report can be viewed at the following URL:
https://www.taishin100.or.jp/100standards/report/5021
---
**[Contact Information for this Matter]**
Secretariat, Seismic Housing 100% Executive Committee
Address: 7F, Akasaka Eight One Building, 2-13-5 Nagata-cho, Chiyoda-ku, Tokyo 100-0014
URL: https://www.taishin100.or.jp/
Keywords: Architecture, Law Revision, Wall Quantity Regulations, Wall Quantity Calculation, Allowable Stress, Living, Seismic Resistance, Seismic Housing, Earthquake, Home
FAQ
What changed with the April 2025 Building Standards Act revision?
Wall quantity standards were reviewed, and the calculation criteria for required wall quantities were modified to account for increased building weight due to energy efficiency measures.
Is "Seismic Grade 3" safe under the new standards?
Yes, simulation results confirm that homes with "Seismic Grade 3" are safe and will not collapse or suffer severe damage under the new standards.
Which is superior, allowable stress calculation or wall quantity calculation?
Allowable stress calculation is superior as it considers more rigorous factors, resulting in more actual wall quantity and allowing for a safer design.