I don't have a source off hand, but I've heard that the average lifespan of a Japanese house is 30-40 years. Sure, there are some historic houses and estates that have lasted for much longer than that, sometimes even centuries. They're built with the intent that a couple will raise a family in them and so there's not much reason for houses to last longer than that. Energy costs are also some of the highest in the world so getting the latest insulation technology and other efficiencies is important.
