Since 2014, when millennials became the largest share of home buyers in the U.S., the number of home and condo sales across the country by co-buyers has soared. The number of co-buyers with different last names increased by 771% between 2014 and 2021, according to data from real-estate analytics firm Attom Data Solution.

The pandemic added fuel to that trend, according to data from the National Association of Realtors. Among all age groups during the early pandemic months—April to June 2020—11% of buyers purchased as an unmarried couple and 3% as “other” (essentially, roommates). Those numbers were up from 9% and 2%, respectively, in the previous year.

A desire for more working and breathing room coupled with high housing prices may have driven this upward trend, says Jessica Lautz, vice president of demographics and behavioral insights for NAR. “During the pandemic, people have been renting and they may have wanted more space,” Dr. Lautz says, “and so they looked at, perhaps, their roommate and decided, ‘Let’s go buy a home together.’ ”