At a conference last week, the former commissioner of New York’s housing department laid out a radical notion: our nation is not building the kinds of urban housing that consumers want. We should therefore continue to refine our building codes to produce more efficient and safer places- but we should spark the market to produce places of different sizes and shapes.

The speaker, Jerilyn Perine, is now the head of a research group called Citizens Housing and Planning Council . She was kicking off a daylong tour of alternative housing types with the cheeky title “One Size Fits Some.” Most of the day belonged to dreamy architects expounding on tiny houses or ginormous “paradigm shifts,” but Perine’s stage-setting should cue developers across the country to think about new models.

The sacrosanct nuclear family for whom we build so much housing makes a modest share of the market. In New York City, Perine said, 17 percent of the market  consists of nuclear families, the same share as couples without children (the so-called DINKs) and about half as much as the reported share of single adults living alone. New York differs from most cities in its proportion of old people and unmarried ones, of course, but demographic trends suggest that the patterns here will affect other cities as our society ages. That means there’s more upside in high-density apartments than you might think from looking at the housing supply.

The new market imperative involves creating effective housing for people who live alone (many of whom, Perine noted, tend to under-occupy big places) and safe, legal housing for young people who share places with unrelated folks. The latter category, Perine said, claims more than a quarter of New York City’s residential market- often in illegal shares of commercially zoned lofts or carved-up single-family homes.

Wouldn’t the first developer to offer a compelling product to either market- say, a house with high-efficiency carbon-fiber partitions you can remove and replace as the household size changes- have a real jump on a commanding share of the market? Acres of empty subdivisions are crying out for help.