How small can a house

be and still be liveable?
There was news yesterday of someone in the United States who has built herself a 7.8m sq house "to minimise her footprint on the environment".  Yes, it is small. There is barely room to move in it.
There is another article in today's paper about living spaces being built into underground nuclear proof, earthquake proof, solar flare proof, pandemic proof bunkers. They are somewhat larger. There is also a swimming pool and the means to grow your own food. People are apparently buying them. (They are rather expensive.)
We live in a perfectly ordinary (for Australia) suburban house. My parents had it built when they retired. Until then they were required to live in housing provided by the Education Department and, for the last few years of their careers, in the house my mother's parents had owned.
The Education Department houses were dreadful. They were made of asbestos sheeting. The same sort of housing has been used for government workers in remote locations all over the state. In one place the land had not been cleared properly and, because the houses are built on stilts, there were small trees growing under the house. In another place the builders had skimped even more on the same design and the rooms were so small I had to sleep on a mattress on the floor. During the day mattress was put up against the wall so that my two sisters and I had a little room to move around the room. In another they had made a mistake with the design and some of the furniture had to go in (and then out of) the living area window. They had to take the glass out and then put it back again. The doorway and the entrance area were too narrow to fit the furniture in that way.
My parents never did anything to these houses. They had to leave them as they found them. Before we moved into one my mother was told that the kitchen was going to be repainted before we arrived. She could choose the colour - cream or grey? She knew precisely which cream and which grey it would be because they were standard colours. She consulted the woman likely to be the next one to use the kitchen and they agreed on grey. They were tired of "departmental cream".
My mother loathed living in the house that had belonged to her mother. This only happened because her mother had died about six months before my parents returned to the city. The house was vacant. It was convenient for my parents to move into it until the estate was settled.  My mother felt her mother's presence all the time. It had not been a happy relationship.
This house was the first one my mother felt was truly hers. It is nothing remarkable. It is, if anything, very ordinary indeed. My mother chose the colour of the walls, the carpet and the curtains. We kept furniture but had some of the upholstery redone.  It was enough for my mother.
Since she has died my father and I have changed very little. We had some very worn carpet removed and replaced with a surface that people often believe is timber. If we could afford to do it and bear the disruption we would do the same throughout the house and do away with needing to clean the bedroom carpets.
We have added just one thing my mother would disapprove of - more bookshelves. There are now three times as many bookshelves in the house. We have brought in books from where they were stored in a shed. We have bought more - certainly more than my mother would approve of.
And that is , I think, what bothers me about the very tiny house and the underground bunker housing. There is no room for books in these places.
I want to be insulated by books.