Builders work on the roof of a home under construction in Jackson Township. Home ownership rates have stagnated in part because high rents have made it difficult for many prospective buyers to amass a down payment.

A diminished supply of available homes is swelling prices in large U.S. metro areas from New York to Miami to Los Angeles, squeezing out would-be buyers and pushing up rents as more people are forced to remain tenants.

The trend is pressuring Americans’ budgets, with about one-third of households spending more than 30 percent of their gross income on housing as of 2015, according to a report being released Friday by Harvard University’s Joint Center for Housing Studies.

Homeownership rates have stagnated in part because high rents have made it difficult for many prospective buyers to amass a down payment for a house.

At the same time, the sparse supply of available properties is benefiting existing homeowners, many of whose home values have recovered from the housing bust a decade ago.

The tight supply of homes and a shortage of affordable rental housing have improved little in recent years for a variety of reasons. Among the key factors is that construction has yet to regain the pace of homebuilding that predated the bust.

“As the economy continues to recover, as income picks up as household formations pick up, it’s not spurring a supply response,” said Chris Herbert, managing director of Harvard’s Joint Center for Housing Studies. “It’s a worsening of the situation that was evident last year.”

Here are some major findings documented in the report:

[naviga:h3]HOUSING AFFORDABILITY[/naviga:h3]

The government considers people who spend over 30 percent of their income on housing to be “cost-burdened.” Those who spend more than 50 percent are considered “severely” burdened.

About one-third of households — 38.9 million — were considered cost-burdened in 2015, down from 39.8 million a year earlier. This was the fifth straight annual decline.

Still, roughly 16 percent of households, or about 18.8 million, paid more than half their income on housing. The share of renters paying more than they can afford varies from city to city. In Miami, it’s 35.4 percent. In El Paso, Texas, it’s just 18.4 percent. Other cities where households were deemed to be cost-burdened include Daytona Beach, Fla.; Riverside, Calif.; and Honolulu.

Ryan Welch of Santa Monica, Calif., is among those feeling stuck between rising rents and home prices. Welch, 32, pays about $1,500 a month for a rent-controlled one-bedroom apartment he shares with his wife. That works out to about a quarter of their monthly income, an affordable portion.

Welch, who works in advertising sales, would like a bigger place with more amenities. But he’s reluctant to leave their apartment.

“I’m nervous to move to a place that’s not rent-controlled,” he said.

Saving to own a home, something he wants to do, has had to take a back seat to making payments on student loans and his car, among other expenses.

“I’d much rather buy, but I can’t come up with the down payment,” Welch said.

HOME SUPPLY AND PRICES

The availability of homes for sale has fallen short of demand. Last year, the typical new home for sale was on the market for just 3.3 months, according to the report — well below the average of 5.1 months dating to the 1980s.

All told, 1.65 million homes were on the market last year, the fewest in 16 years, the report said.

The supply is worse for lower-priced homes that would be affordable to typical first-time buyers. Builders have been constructing fewer homes for that segment of buyers.

Between 2004 and 2015, construction of single-family homes of less than 1,800 square feet fell to 136,000 from nearly 500,000, according to the report.