I don't really follow. The idea for roads is that congestion moderates the utility of roads, so over a wide range of capacities roads will remain congested or

I don't really follow. The idea for roads is that congestion moderates the utility of roads, so over a wide range of capacities roads will remain congested or even become more congested as you add roads, since if you build more you make the roads more useful (reaching more places faster, through better connections or increased capacity) and so people will use them more, potentially resulting in more congestion but almost certainly not less. The parallel idea for housing would be that cost moderates the utility of the city, people move into the city until the cost matches the benefits of density for them (driving up costs and pushing out people for whom the equation no longer works out). If you add units, you've just allowed more people to move from Idaho into the city, and made the entire city potentially more valuable from increased network effect and caused costs to go up further. This process shouldn't be expected make it affordable to live in the city, unless you've managed to either damage the utility of living in the city through the secondary effects of increased population/density or you've managed to build enough supply the you can sink the entire worldwide demand for living in one of the best and most valuable place, such that there are no more wealthier people anywhere in the world to sell to and you must go down market to get more customers. It would however, increase the number of people who can have the benefits of living there, but at the cost of displacing more people who can no longer afford it... the benefits go to people outside of the city: The wealthy ones that can move into the city, and the rest who enjoy lower competition for housing outside of the city. > Denser housing is very efficient Housing itself increases in efficiency to a moderate level of density-- a duplex is somewhat more efficient to construct than a single family home, owing mostly to reduced land costs (materials are somewhat higher due to the increased isolation and fire protection required). But the effects fall off with increasing density, and you run into issues that building higher involves structural and safety related costs that hurt their efficiency. E.g. https://ti.org/pdfs/APB36.pdf https://ti.org/pdfs/APB36.pdf Page 2-- high-density construction is significantly greater, per square foot, than low-density construction. Due to the increased need for steel, concrete, and similar materials, the cost of building three or more stories is progressively greater the more stories are built [...] building three stories costs 30 to 50 percent more, per square foot, than two-stories; four to seven stories costs 200 to 300 percent more; and eight or more stories costs 450 to 650 percent more" )