I should clarify a point here. When I talk about small spaces, I’m not talking about photogenic shelters constructed from found materials by Silicon Valley billionaires. I am not talking about cabin porn. I am talking about the universal human instinct to burrow, regardless of your personal dimensions. “There is a kind of play common to nearly every child; it is to get under a piece of furniture or some extemporized shelter of his own and to exclaim that he is in a ‘house’ ” wrote the British architectural historian John Summerson in his 1949 essay collection, “Heavenly Mansions.” None of us, Summerson writes, entirely outgrow our love of “squatting under the table.”