Millions of young adults who moved back with their parents this year could lead to an estimated $726 million in lost rent, according to a Zillow analysis, which noted that the ripple effects "could have far-reaching consequences for the housing market."

Amid high U.S. unemployment in the coronavirus pandemic, the number of adults living in a parent's or grandparent's home grew by more than 2.7 million in March and April, said Zillow, adding that the vast majority of those who moved home — about 2.2 million — are from Generation Z and are between 18 and 25 years old.

Zillow said the 2.2 million Gen Zers represent an estimated $726 million in rent payments each month — about 1.4% of the rental market at risk. "It is highly unlikely that all leases will be broken and this full amount would go unpaid, but it serves as a gauge of the potential impact on housing," the Thursday report said.

What happens next to this population could impact the housing market's near future, the report said. For instance, if jobs are permanently lost or slower to recover than expected, that could free up many rental units and drive down prices.

Even before the pandemic, the number of adults living with their parents was high after the last financial crisis, as millennials flocked to the basements and spare bedrooms of Baby Boomers.

"Now, it's Gen Z's turn to ride out today's crisis amid massive unemployment," Zillow Senior Principal Economist Skylar Olsen, was quoted as saying. "But this time, rents are more likely to slow, easing the path to returning to living on their own even if some under-employment persists."

As apartment construction has exceeded "historic norms" in recent years, Olsen said, some young adults are likely to double up or live more affordably in various ways, which should soften rent growth.

Meanwhile, living with parents rent-free, and staying even after jobs return, could allow some Gen Zers to save enough for homeownership more quickly or may even delay their parents from downsizing into a smaller home, Zillow noted.

Cities with a higher share of young renters may see a disproportionate impact. This includes Austin, Kansas City, Cincinnati and Pittsburgh, Zillow said. On the other end are areas with more millennials and older renters, including Miami, New York and Los Angeles, which each have less than 1% of the rental market made up of young people who have moved home, Zillow said.