I am on the markert for a good home builder and have been reading sites like [https://reform-meister.jp/housemaker/615/](https://reform-meister.jp/housemaker/615/) .
So far I have gathered good information on multiple areas but not a lot of clarity on airtightness and insulation ratings per home maker. Any sites or information is greatly appreciated.
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When I was shopping around for a home builder I was asking the same question. Eventually, I realized that all homemakers said that their houses were warm in winter and cool in summer. Then they show you a cross-section of a typical wall with a bunch of materials and figures and sure, that looks like enough insulation, I guess. Kind of hard to compare different house makers so then I figured I would compare airtightness figures but realized that a lot of builders don’t publish those figures.
Another approach might be to look at builders that have won the House of the Year Award in Energy, or at least applied. I don’t know what their criteria is and it seems like a lot of companies have won awards but it might give you some new leads. [http://www.jcadr.or.jp/HOYE/](http://www.jcadr.or.jp/HOYE/) Another idea is to search for home builders whose places have BELS (ベルス) mark, basically an indicator of how energy efficient their homes are.
We built with Hokushu. They are an Iwate based company, so insulation is 150mm rather than 100mm. We are in Miyagi. There is some kind of membrane which they used to “seal” the house but not sure how legit it really is. Lived here for 5 years, far better than the crappy rentals I lived in before, but still hot in summer and cold in winter.
Edit: didn’t totally answer your question I realize! Just my anecdote!
Don’t know what Japanese level you or your partner have, but highly recommend this YouTube channel if your looking to build a home. https://youtube.com/channel/UCMzddq7FBK8DiP9-KPzhj9Q
There’s loads of great info, and the also have videos with home builders who specialize in that type of building. I think I even saw a video on their channel listing home builders with good specs but I can’t seem to find it right now. I’ll post it if I do find it though. Also, what general area are you guys in? Would help narrow down a lot.
[Ichijo](https://www.ichijo.co.jp) has been pointed out here before, if you’re in a location that they serve. Sweden House probably also good. There’ve been some very knowledgeable comments on houses in the past here, searches on ichijo might lead you to those.
Of course, it depends on your budget…
It’s from 2020, but i imagine it hasn’t changed much in 2 years: https://matsuosekkei.com/comparison/
What are your top 3 places so far?
Contact Passive House Japan and use a builder they recommend.
There’s thick insulation and air tight and then PH which is on another level.
This is what we did and live now in a house with full central air and miniscule electric bills.
By the way, here is a good site that a person explains insulation and airtightness in a sensible manner. I found it while researching and i think they would be good aditions to the wiki
insulation
https://good-things-committee.com/column/1000
airtightness
https://good-things-committee.com/column/1025
also found this interview with a japanese architect that does passive house designs.
https://tokyocheapo.com/living/interview-miwa-mori-passive-house-japan/
We just finished designing our house with good airtightness and insulation. If you can speak Japanese, we had a fruitful meeting with [https://sml-support.com/](https://sml-support.com/) who then introduced us to 3 or 4 builders who can build well insulated houses in the area we purchased our land. We decided to go with Lohasta based on their style and our budget. You can have a look at their specs here [https://lohasta.jp/grade/](https://lohasta.jp/grade/) (but it appears their site is down tonight).
We went with Serara Koubou, a lesser known contractor in the Yokohama area. They’re much cheaper than a lot of similar competitors because they rarely advertise, but we do have great insulation. I can’t give specific numbers though since I don’t know how to measure that.
https://serara.jp/
Not sure about airtightness/insulation but Selco Home is sort of famous for the handful of homes in Sendai that didn’t collapse/get washed away in the 2011 earthquake.
[https://selcohome.jp/](https://selcohome.jp/)
Only reason I suggest them is because it seems a lot of homebuilders are not building homes that last, but possibly selco is.
Just throwing the name out there in case you hadn’t heard of them. Sorry I can’t be of any more help than that and best of luck!
A lot of the major homemakers won’t publish their ratings, and even if they do, it is usually only for their highest tier of house. For example, Ichijo has great airtightness ratings, but that is when you are talking about their i-smart series. You best bet if you want a well insulated, highly airtight, energy efficient house is to contact a builder or architect that is in the Passive House Japan Association. These are architects and builders that share a common interest/goal in making efficient housing. The vast majority of the houses they build are not passive house certified (mostly due to the cost of it), but they are all able to build well insulated, highly airtight houses.
We found our architect on that website, who sat down with us, and listened to what we wanted. He drew up the plans, chose the construction company (with our approval of course), and managed the project from start to finish. We moved into our new home just over a year ago, and have been exceptionally happy with it’s performance (a single 6-mat aircon services the whole house). Our house has a UA rating of 0.28 and a C rating of 0.3, it is BELLS certified also.
The one caveat is that these things do not come cheap. In another comment you said you have a budget of around 2000-3000万 for the building, which is going to be difficult with those specifications, unless it is quite a small build.
If you are seeking for better airtightness and insulation, what you want to look at is what kind of material you would like to use as insulation instead of looking at the ranking of house builders.
Currently the urethane form has the most shares, and [Aqua form](https://kensetsu.ipros.jp/ranking/product/category/3/140163/) is probably the most material used.
I believe any 気密断熱 house builders are able to use it as the insulation material. What is left is your budget.
For me, if I have enough space, and budget I would choose a 外断熱 (external wall insulation) house with any house builders.
外断熱 is a bit pricey option + not so many builders are able to perform, but you will have less condensation + better thermal efficiency inside the house.
Type 外断熱の家 + your area in Japanese on google. Good luck!