Dr. Bakko's Structural LAB.

For the people who wants to live in Japan safely

Exploring of Housing exhibition: Check the sales person

I like visiting a model room. I also like visiting a model house. In housing exhibition, we can see a lot of houses at once. I tend to ask a maniac question unintentionally.


□■□ Question ■□■

Is a sales person at housing exhibition reliable?


□■□ Answer ■□■

They study hard and don’t tell a lie. But some staff tells us wrong information due to misunderstand.



Case of uncle working at Reinforced concrete house manufacturers

Generally reinforced concrete house manufacturers adopt TAISHIN (earthquake resistant) structure. There are a few manufacturers offering option of MENSHIN (seismic isolation), but no manufacturers adopt SEISHIN (vibration control).

(Difference of TAISHIN, SEISHIN and MENSHIN, refer past article)


Uncle: “In the case of SEISHIN, dampers (the device which reduce building vibration) don’t work unless building gets deformed. Reinforced concrete house has high stiffness so that originally it doesn’t deform. For reinforced concrete house, TAISHIN is the best solution.”


It is right. To be more correct, “reinforced concrete house with wall structure”. But it’s small mistake. Improvement of performance under earthquake by adding dampers is small for that house. Considering value for money, TAISHIN is the best.


Case of young man working at Steel house manufacturers

Generally steel house manufacturers adopt SEISHIN. Many kinds of dampers are used for those houses, “oil-damper”, “visco-elastic damper” and “steel damper”. There are few manufacturers which have only TAISHIN.


Young man: “Our steel dampers are sophisticated. It can absorb energy of earthquake and reduce seismic intensity 6 to seismic intensity 3.”


Steel houses tend to be softer. So, there is large room that the dampers show its performance. But, even if very superior dampers are installed, the shaking of 1st floor is equal to the base. 1st floor is connected to the base through the stiff foundation, shaking of earthquake directly propagate to. Besides, in the case of low rise building like single house, it is very rare that the shaking of 2nd floor or roof become lower than that of base or foundation.


I correct other part. Not “energy of earthquake”, but “energy of house vibration caused by earthquake”. It’s a drop in the bucket even if absorbing few energy of huge earthquake energy.


“Reducing seismic intensity” is also strange expression. It’s a shaking degree of the base, not building. No engineer says “shaking degree of this building is seismic intensity 3”.


You might think it’s a nitpicking, but specialists use words with care due to their responsibility. I would like this young man to study more. Of course, he told me a lot of new things except structure.


Case of executive working at Wooden house manufacturers

I have met an executive at housing exhibition by chance. He was interested in my career which I filled in the pre-questionnaire and talked to me.


He told me a motion of housing market, difference of condo interior between developers and so on. He also told me that they focus on education of employees, for example inviting a structural engineer to hold seminar. I am relieved when I listen to such story.


Some wooden house manufacturers adopt SEISHIN, and deal various dampers. But differ to steel house, there are many manufacturers which only offer TAISHIN.


Executive: “In the past, we recommended SEISHIN, but now, our main line up is TAISHIN. There are few differences between TAISHIN and SEISHIN because of improvement of walls. It is not necessary if there are no differences until it experiences big earthquakes like seismic intensity 6 several times.”


He probably read the paper from R&D department very well. In the case of using high performance walls, houses don’t deform a lot and there are few rooms that dampers show its performance.


Even if walls are very strong, it will get damaged after several big earthquakes. As another merit of dampers, it hardly gets reduced its performance. In the case of weak building, the difference of walls and dampers appear after one big earthquake. But in the case of strong building, as is in the executive remark, there is possibility that the difference may never appear.


It may be fresh memory that Kumamoto earthquake caused seismic intensity 7 to same place 2 times. After that earthquake, advertisement message like “it could tolerate seismic intensity 7 ○○ times” or “strong house against repeated earthquakes” increased. Of course, it is an important element, but you should set margin which you feel appropriate.


What kind of people are there in housing exhibition

Basically, the people in reception are part-timers. Week days are also business time, so there are many house wives, too. The people who explain the house after reception are temporary staff or full-time employees, and their backgrounds are variety.


Not only people who graduated from department of architecture, but also who graduated law, economy, electronics, and so on. Encountering an architect is not so usual. I’ve never encountered Structural-design First-class Architect in housing exhibition. I heard that some companies send a person who has Ph.D. once in a while.


First-class Architects looks having composure in their correspondences. They probably have pride as a specialist. But when they affirmed something about structural engineering, I sometimes felt a little aversion. There are many things to be solved in that field. We can’t affirm with careless.


The person who becomes humble suddenly after looking at occupation field of questionnaire might not be reliable.


Totally, they study well. You ask everything what you want to know honestly. Studying thorough this blog before going to housing exhibition may be a help to judge sales person is excellent or not.