Do some reading about "the missing middle." In many cases the sort of medium-density housing like row houses or duplex/triplex/quadruplex designs that offer more comfort and privacy than a massive apartment complex but are more affordable than single family houses on large lots are explicitly regulated against in American cities, and local codes need to change in order to allow the sort of humane-but-cost-effective housing that will make a dent in the affordability crisis. Problem is, though, that existing homeowners see denser housing as a threat, both to the value of their own properties, and to the comfortable social homogeneity of their neighborhoods. At some level you need to have the power to force these developments through over the objections of the neighbors, undemocratic as that is, or else the problem never gets solved.