[alistairSH]

Also, space can be 'modest' in size rather than 'tiny' and still be sustainable or amenable to high density.

And in most of the US, we can increase density massively without reducing size to “tiny” or even “small” sizes. The norm in the US is a single-family home (~70%, including townhomes). We could build a lot more large apartment/condo buildings. A lot more duplexes. Both are rare in most of the US. Apartments are almost exclusively targeted at younger, childless people and rarely more than 2 bedrooms.

[bsder]

The problem is neighbors.

The reason why everybody wants a detached home is so you don't share a wall or floor with a neighbor.

Dense housing could be built so that you are well isolated--unfortunately, it never is. Consequently, you have to deal with stomping upstairs, dogs that bark all day, etc.

If people are truly interested in dense housing, we'll need some building codes that make building it a bit more expensive.

[alistairSH]

Agreed. Apartments are largely viewed as temporary and not for families - thus they’re built cheaply and not big enough (to meet American family expectations). The current 5-over-1 trend is awful in this regard. Yeah, it’s inexpensive to build, but light wood framing done to a tight budget leads to noisy, smelly, awful places to own or live long-term.

[ClumsyPilot]

Apartments in dense cities are worth millions of dollars, and yet their construction quality is surpassed by some soviet brutalism from the previous century.

Also laws and planning for apartments and leaseholds are absolutely atrocious in UK and most contries that do not have a socialist past - people in charge just do not understand how to deal with them.