Low housing supply is leading to high rental prices all across the United States, but in San Francisco the situation is worse than in nearly every other metro area in the country, according to a new report from real estate website Zillow. Renters in the five-county San Francisco metropolitan area (San Francisco, Alameda, Contra Costa, Marin, and San Mateo counties) spend an average of 44 percent of their monthly income on rent, a figure that comes in behind only Los Angeles' 48.2 percent. The Zillow report found that areas with slow population growth or high rates of new construction were more affordable, while metros like San Francisco, where there were just 193 new housing units permitted for every new 1,000 residents, saw prices soar.

That figure (only 193 units created for every new 1,000 residents) is about in line with Paragon Real Estate's recent, and equally depressing, report noting that San Francisco proper built only 7,500 new housing units for the 45,000-strong population bump the city has seen since 2010, a longer timespan than Zillow's report.

The national average rate of building was 384 new units for every 1,000 new residents according to Zillow, which looked at permits issued in 2012 and 2013 and population growth between 2012 and 2014. Los Angeles had an even lower building rate than San Francisco, constructing just 187 new units for every thousand new residents. Cities that built lots of new housing, like Chicago, were more affordable for renters. Chicago built 906 new units for every 1,000 new Chicagoans, and median rents in the city were 31.1 percent of median area income.

Unsurprisingly, the situation doesn't look much better for homeowners in San Francisco. A monthly mortgage in the San Francisco metro area costs 39.2 percent of the area's median income, again behind Los Angeles, where a mortgage payment is 40.1 percent of median income.

· Low Housing Supply Squeezes Affordability [Zillow]

· SF's Population Is Growing Way Faster Than Its Housing Stock [Curbed SF]

· SF Now Has More Than 50,000 Units in the Housing Pipeline [Curbed SF]