Housing supply gap for owner occupied houses: 4 million, says Freddie Mac

Recent related entry:

-- "Understanding the DC housing market: demand for urban living, not the construction of new housing, is the driving force"

Again, there's nothing particularly unique about the US "housing crisis."  The problem comes down to not enough housing relative to demand, which is exacerbated by various factors including the fact that the most desirable places are already, for the most part, built out.

And that the preference for single family housing is increasingly difficult to satisfy in the core of metropolitan areas, especially center cities, which have been pretty much built out for decades:

• leading to calls for intensification and equally voluble opposition to such 
• adding accessory dwelling units to single family houses ("DC and accessory dwelling units")
• and other forms of "missing middle housing"
• eliminating single family housing districts altogether by allowing duplexes and triplexes ("Massachusetts Triple Deckers as "Missing Middle Housing" -- triplexes", and
• building multiunit housing in areas that had mostly been single family.

The Wall Street Journal reported ("U.S. Housing Market Is Nearly 4 Million Homes Short of Buyer Demand") on a study ("One of the Most Important Challenges our Industry will Face: The Significant Shortage of Starter Homes") by the mortgage financing entity Freddie Mac estimating the gap in housing supply, which they discuss in two reports:

-- The Housing Supply Shortage: State of the States
-- The Major Challenge of Inadequate U.S. Housing Supply

From the second report: 

... we discussed two main reasons for the lower levels of housing production (relative to population): increase in development costs and shortage of skilled labor. 

 Home building costs encompass the cost of land and regulatory costs. Since 2010, the cost of land has averaged about 23 percent of total home building expenses.1 But in some markets like San Jose, Santa Ana, Oakland, and Los Angeles, land can cost upward of 70 percent of the cost of building a home. Laws and regulations such as local zoning restrictions on lot sizes and building height and open space designations also increase the cost of building a home, in turn reducing the supply of new homes. Regulatory costs increased 29 percent between 2011 and 2016, the National Association of Home Builders (NAHB) estimates.

The problem of "development costs" is somewhat subtle.  First has to do with the predominate preference.  People want single family houses, ideally centrally located.

Second, in the core of a region, those locations are already built out, usually in ways that didn't use land in efficient ways, at least in terms of having to house a population 1.5 times larger than when most of those places were developed.

Since there isn't much land available, except in commercial areas, and so when it is developed, it is developed primarily as multiunit, and outside of the core of major metropolitan areas, there is still reticence to live in such a housing type.

This produces sprawl, because to buy a single family house, for the most part it is only on the edges of a metropolitan area where the land costs are low enough to build such housing.

Depending on the market, like here in Salt Lake, there is a variant, of jamming in rowhouse type houses in on odd bits of land, often perpendicular to the street, in a way to maximize the number of units that can be produced ("Gentle Infill: Boomtowns Are Making Room for Skinny Homes, Granny Flats, and Other Affordable Housing," Lincoln Land Institute, Infill Design Toolkit, City of Portland).