Hiramatsu Architecture Co., Ltd.
Just under 90% of residents of single-family homes based on the old earthquake resistance standards, and more than half of them based on the 2000 standards, are worried about their homes’ earthquake resistance.A home building professional explains! “Characteristics of houses that collapse in earthquakes”
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According to Ishikawa Prefecture, more than 49,000 homes were damaged in the Noto Peninsula earthquake. Furthermore, according to the “Estimation method and target for seismic retrofitting rate of houses and buildings” released by the Ministry of Land, Infrastructure, Transport and Tourism in 2020, as of 2018, the seismic retrofitting rate of detached houses nationwide was approximately 81%. It is estimated that approximately 5.6 million homes have “insufficient earthquake resistance.”
Therefore, Hiramatsu Kenchiku Co., Ltd., which designs and builds “houses that are friendly to people, the earth, and household finances,” with the aim of looking back 100 years from now, is targeting 1,000 men and women aged 25 to 65 nationwide who live in single-family homes. We conducted a survey on “anxiety at home and countermeasures against a major earthquake.”
[Image 1: https://prtimes.jp/i/129720/6/resize/d129720-6-3df4778ca46626318920-0.jpg&s3=129720-6-c839a8fd3e99a35c2412478ee5c3c2cc-1077×720.jpg] Survey overview
Survey period: February 2, 2024
Research method: Internet survey
Survey target: Men and women aged 25 to under 65 living in detached houses (owner-owned homes) nationwide
Sample size: 1,000 people
Research institution: Freeeasy
*When using the survey results in this release, please indicate “Research by Hiramatsu Kenchiku Co., Ltd.”
Survey results summary
・76% of detached houses are made of wood
・There is a higher degree of anxiety about the home than in a house that complies with the “old earthquake resistance standards” built before 1981, but no earthquake countermeasures have been taken. Investigation result
When asked, “What is the structure of your home?”, the responses were “wooden construction” (76.2%), “steel construction” (19.4%), and “concrete construction” (4.4%).
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Homes in Japan have earthquake resistance standards stipulated by the Building Standards Act, including the “old earthquake resistance standards” before June 1981, the “new earthquake resistance standards” after June 1981, and the “2000 earthquake resistance standards” after June 2000. It is broadly classified into three periods based on 2015. When we asked the 762 people who answered “Wooden construction”, “When was their home built?”, the overwhelming majority answered “After 2000” (71.7%), “After 1981” (15.2%), and “After 1981″ (15.2%). Only a few people answered, “Before 1981” (6.7%) or “I don’t know” (6.4%).
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We asked those who answered “Before 1981”, “After 1981”, and “After 2000”, “Are you worried about your home, such as whether there is a risk of it collapsing in a major earthquake?” Before 1981, the most common answer was “very worried” (58.8%), after 1981, “somewhat worried” (53.4%), and after 2000, “not very worried” (36.3%), and the older the house, the higher the anxiety level. The results were also high.
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Next, when asked, “Have you taken any measures to prepare for a major earthquake?”, over 80% (84.4%) answered before 1981, just under 80% (76.2%) answered after 1981, and 60% said after 2000. A weak majority (58.4%) answered, “I haven’t done anything in particular,” indicating that the older the house, the more anxious they are about a major earthquake, but they haven’t taken any precautions.
On the other hand, since 2000, 31.9% have lived in homes that are “earthquake resistant (earthquake resistance grade 3)” and have undergone “earthquake resistance diagnosis” (10.1%) and “earthquake reinforcement” (4.4%). More than 40% (41.6%) took some kind of countermeasure.
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Craftsman CEO Akinobu Hiramatsu explains the characteristics of houses that collapse in earthquakes
Earthquake risks and countermeasures
In order to accurately understand the risk of earthquakes, we need to learn from the past. According to “Nikkei Home Builder” (September 2020 issue), more than half of the houses in the area affected by the Kumamoto Earthquake did not survive. I believe that some of the houses that collapsed in this earthquake met earthquake resistance standards that are not a problem under the Building Standards Act. However, homes built before 1981 that do not meet seismic standards are particularly susceptible to collapse or damage.
Even in the current Noto Peninsula earthquake, most of the damage was probably caused by houses that were built before earthquake resistance standards were established or were old.
Earthquake resistance standards are the “minimum earthquake resistance standards that must be met” for buildings to be
constructed by the government. It is broadly classified into three periods: “earthquake resistance standards” and “2000 standards” after June 2000. The 2000 Standards were established in response to the Great Hanshin-Awaji Earthquake, and from 2000, an “earthquake resistance grade” was also established as an index of earthquake resistance. Earthquake resistance grades are divided into three levels from 1 to 3. 1 is a level that meets the level of seismic performance required by the Building Standards Act, 2 is 1.25 times stronger than standard 1, and 3 is 1.5 times stronger than standard 1.
Looking at the figure below “Damage ratio of wooden houses by construction period during the Kumamoto Earthquake” (from a survey in the center of Mashiki town conducted by the Architectural Institute of Japan) (*1), only 5.1% of wooden houses under the old earthquake resistance standards had no damage. There is only that. Even in wooden houses based on 2000 standards, the rate of no damage was 61.4%. Would you be concerned if I told you that there is a 40% chance that damage will occur when you buy a house? If you are going to buy a house, it must be built to a level where there is no risk of earthquakes and you don’t have to worry about it.
Complying with the Japanese Building Standards Act does not mean you can feel safe, and seismic grade 3 is a necessary condition, but even seismic grade 3 is not rock-solid. Even if your building has moderate or minor damage and looks okay from the outside, it could be dangerous if the next earthquake hits. As the shaking becomes progressively louder, nails begin to fall out and joints become loose, gradually reducing the strength of the house.
For this reason, it is important to build houses that can withstand repeated earthquakes. Houses with load-bearing walls housed within pillars are strong.
(*1) Publisher: Kumamoto Type Housing Producers Federation
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Additionally, according to the Japan Meteorological Agency’s “Seismic Intensity Database,” there were 398 earthquakes with a seismic intensity of lower 5 or higher between 1990 and 2023. On average, there are 11.7 earthquakes with a seismic intensity of lower 5 or higher in a year. Living in Japan, there is a risk of earthquakes no matter where you live, so I think it is necessary to build a house that is highly earthquake resistant.
[Image 7: https://prtimes.jp/i/129720/6/resize/d129720-6-d1c1fad4920febc83c4c-6.jpg&s3=129720-6-5986ac79019dc315c681dfd6d2f40fd6-1280×543.jpg] I think one of the reasons why houses with low seismic resistance ratings are being built in a country with so many earthquakes is because of the Building Standards Act’s “Special Provision 4 (*2)”. Special Provision 4 is a special provision in which small wooden buildings with two floors or a total area of 500 square meters or less do not need to attach a structural calculation report, and are allowed to skip the structural examination. Therefore, it is more likely to collapse. This does not mean that you can feel safe as long as your home is built in accordance with the Building Standards Act. Under the 2025 law revision, wooden buildings with two or more floors or a total area of more than 200 square meters will be classified as “New Buildings No. 2” and will be required to attach a structural calculation report, but this alone will not provide peace of mind. In addition to seismic grade 3, it is important to perform the highest level structural calculation called “allowable stress calculation”. (*2) In the revised Building Standards Law scheduled to go into effect in April 2025, special provisions No. 4 will be reduced.
Measures for people who are about to build a house
The following three conditions are very important when building a house. ・Earthquake resistance grade 3
・Allowable stress calculation
・Ensuring construction quality (*3)
(*3) Is the construction actually being carried out according to the original design? Are there any fine nails or pins? Are the structural hardware properly attached? We will conduct a thorough construction management audit to ensure the construction of a reliable home. Measures for those who have already built a house
People who have already built a house need to consider proper countermeasures. First, it would be a good idea to conduct an earthquake resistance diagnosis to understand the current state of your home’s strength, and then strengthen it to make it earthquake resistant.
Subsidized projects (subsidy systems) are implemented in many local governments for earthquake resistance diagnosis and earthquake reinforcement. Please contact your local construction company or local government.
Earthquake reinforcement
There are two main methods of seismic reinforcement.
The first is to make the building lighter. During the Noto Peninsula Earthquake, some houses were damaged by roofs shaking and tiles falling. Heavy roof tiles put a strain on the building and may cause it to collapse, so it is necessary to make the roof lighter. There would be no problem if the house was built with proper construction methods and structural calculations to match the weight of the tiles, but the reality is that many houses do not do this. First of all, we recommend replacing heavy roofs such as tiles with galvalume steel plate roofs. If the roof is lighter, the center of gravity of the building will be lowered, which will strengthen the building against earthquakes.
Additionally, if solar panels are retrofitted for renovation after earthquake reinforcement, the roof will be heavier than originally expected, which may cause problems with earthquake resistance. be careful.
The second step is to reinforce the exterior walls and foundations. Since June 1981, it has become mandatory to include reinforcing bars in the concrete foundations of houses, but since it was optional for houses before then, many houses are made of “unreinforced concrete” without reinforcing bars. Because there are no reinforcing bars, the strength of the foundation is low, and its durability against earthquakes and other forces is also weak. Reinforcement of
unreinforced concrete foundations like this can be done using a method called additional pouring. Another seismic reinforcement method is to wrap carbon fiber sheets around the foundation. In addition, if the building is properly braced to strengthen its seismic resistance against horizontal tremors, or if the building is made with solid walls, it will become extremely resistant to repeated shaking. However, the reinforcement method will vary depending on the site situation and budget, so it is best to conduct a detailed diagnosis of the building and consult with a local construction company before proceeding.
The cost of seismic reinforcement varies depending on the age of the building, the condition of the house, etc., and is by no means cheap. Although not everyone can do this, I would like those who can afford it financially or those who plan to live in the house for a long time to seriously consider it so that they can continue to live with peace of mind.
Profile of craftsman president Akinobu Hiramatsu
[Image 8: https://prtimes.jp/i/129720/6/resize/d129720-6-03c017320adb34c6a125-7.jpg&s3=129720-6-a62fb8c7a927b6c541723910c00e7597-3305×2358.jpg] Born in 1980 in Iwata City, Shizuoka Prefecture.
I have loved making things since I was little, and started working as a carpenter at the age of 19. Over the past 10 years, he has demolished and repaired more than 100 decades-old homes, and has learned the characteristics of building durable homes and those that break down quickly. While gaining experience in numerous workplaces, he acquired various qualifications and became independent in his 10th year. Founded Hiramatsu Kenchiku as a private business at the age of 29. Established a corporation as Hiramatsu Kenchiku Co., Ltd. at the age of 32. Annual sales: 1 billion, number of employees: 25 (as of 2024)
While running a construction company, he holds lectures nationwide for construction companies in the same industry, with the theme being construction companies that propose better home construction. We also have many experience consulting for construction companies in the same industry. I will go to Germany to learn about energy-saving and healthy living. When an earthquake occurs, we go to the site to gather information, use primary information to determine the important aspects of building a house, and continue to research how to build a house that suits the local climate and features.
The number of new housing constructions exceeds 180. In 2021, he published “Money Saving House 3.0 – A “Living House” where you can save 2 million yen just by living in” (Canary Communications). In 2022, at the request of the Shizuoka Prefectural Government, we will hold a training session on how to proceed with construction DX for housing companies. In 2023, he published “House Encyclopedia: How to choose, build, and live in a comfortable home” (KADOKAWA). The YouTube channel “Craftsman President’s Home Construction Contractor” has posted 365 days in a row. Over 100,000 channel subscribers and 33 million total views.
YouTube: https://www.youtube.com/@hiramatsukenchiku/
Company Profile
Trade name: Hiramatsu Kenchiku Co., Ltd.
Location: 350-3 Kodateno, Iwata City, Shizuoka Prefecture
Representative: Representative Director Akinobu Hiramatsu
Founded: February 25, 2009
Business content: New construction of zero-energy houses, new construction using the WB construction method, general renovation work, various housing loan application services, land search introduction services
Phone number: 0538-74-3343
URL: https://www.hiramatsu-kenchiku.jp/
Instagram: https://www.instagram.com/hiramatsu__kenchiku/
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