SEATTLE (11/16/15)--Escalating housing rental prices continue to gobble up larger shares of income and, with it, the savings that could translate into down payments for purchasing a home.

In the third quarter, home buyers will spend roughly 15% of their monthly income on mortgage payments, while renters will spend roughly 30%, according to numbers released last week by Zillow.

Furthermore, rental affordability is worse than historic norms in 34 out of the 35 largest U.S. metros, illustrating that the issue is widespread.

“Comparatively low monthly mortgage payments, coupled with increasingly expensive rents, continue to make homeownership a relative bargain to millennials and other potential home buyers. But there’s a catch,” said Meredith Miller, from Zillow. “Getting the best interest rate on a mortgage, and the low monthly payments that come with it, typically requires a down payment of tens of thousands of dollars … Coming up with that kind of cash is increasingly difficult as rents and home values alike continue to rise.”

For example, a home buyer earning the national median income of $54,990 planning to purchase a median-priced home at $182,500 in the third quarter would pay 15% of their income towards mortgage payments. To rent a typical home, however, it would cost the same buyer 30% of his or her income.

The mortgage payments are cheaper, but only if the buyer can come up with the roughly $36,500 down payment needed to purchase the home.

“Of course, smaller down payments are an option for many, but also often come with higher interest rates and private mortgage insurance,” Miller said, adding that “both conspire to raise monthly payments and consume a larger share of monthly income.”