> Homes in Hokkaido area, where it gets quite cold in winter, have good insulation.
Define "good insulation". I live in Aomori prefecture and most houses here have terrible insulation, and when I visited Hokkaido it didn't look much better. There is a reason why home centers sell lots of different materials to insulate the house yourself, because the construction itself is awful.
I think it depends if the house was pre-built or meant for rentals. I had the unfortunate experience of buying a used pre-built house in the Tokyo area and it was terrible. Every room vented directly outside, windows were single pane with bare framing, and it felt like it had only token insulation. Same with rental apartments, with the only benefit being small places.
The builders I've worked with; Tokyu Homes and Seksui House build all over Japan and have a catalog of options catered for each region. ie: Kanto (Tokyo area), Tohoku (Aomori), Hokkaido, etc. The contents of the catalog are surprisingly different. For example, triple pane glass and heat exchangers for ventilation is not shown in Kanto catalog.
My ex-partner was an architect and I have a strong interest in things mechanical. Along with experience of having multiple homes built for us and with a western attitude, we were able get a livable house that's fairly efficient (for a Western lifestyle).
Define "good insulation". I live in Aomori prefecture and most houses here have terrible insulation, and when I visited Hokkaido it didn't look much better. There is a reason why home centers sell lots of different materials to insulate the house yourself, because the construction itself is awful.