Well, that's the minimum boundary recommended, and they cite what the Swiss Government guarantees in the shelters. I would assume you'd try to get more, but the

Well, that's the minimum boundary recommended, and they cite what the Swiss Government guarantees in the shelters. I would assume you'd try to get more, but then your size requirements for such a shelter rapidly grow. I think it would go without saying that people would have to get used to vasty different living arrangements should the need to relocate to a bomb-shelter arise. Creating a shelter that is fit for purpose in protecting people from the bomb blast and fallout and also providing a suitable living space is an expensive and resource consuming endeavor, the least of which is just getting enough space somewhere.