A rental vacancy sign is posted in front of an apartment in San Francisco. High rents, according to a recent study, are one reason a large number of millennials are living at home with their parents or living with roommates. (Justin Sullivan/Getty Images)

If you’re a millennial living with a roommate or your parents, you’re hardly alone. In fact, nearly one-third of people in your age group are in that predicament, a substantial increase in the past few decades.

In 1990, 19.7 percent of young adults ages 25 to 34 lived with relatives or roommates, according to the National Association of Home Builders (NAHB). In 2016, that number reached 33.8 percent.

Naturally, the states with the largest percent of millennials sharing their homes are those with the most expensive housing, such as California, Hawaii and New York. The District has the highest share of 25- to−34-year-olds living with roommates or housemates: 20 percent.

Recent analysis by ATTOM Data Solutions, a property data site based in Irvine, Calif., found the number of people buying homes with co-buyers is increasing regardless of whether they own or rent. Co-buyers are defined as multiple, non-married buyers listed on the sales deed. Nationwide, 17.4 percent of all single-family home purchases during the first quarter of 2018 included a co-buyer.

Metro areas with the highest percentage of co-buyers include San Jose, San Francisco, Seattle, Honolulu and Miami. The average down payment for homes purchased by co-buyers was $56,911, 46 percent higher than the average down payment of $38,917 for homes without co-buyers. The average down payment for co-buyer purchases was 15.3 percent, 35 percent higher than the average down payment of 11.4 percent for other home buyers.

To read more of NAHB’s research, click here.

For more information about co-buying trends from ATTOM, click here.