National home values rose just 0.2 percent in January from December, according to a new report from real estate portal Zillow, the smallest monthly increase since May 2012.

Increasing inventory is helping to slow the growth in home prices nationwide, the report suggests. Nationwide, while inventory remains tight, the number of homes listed for sale on Zillow was up 11.1 percent annually in January on a seasonally adjusted basis, the fifth straight month of rising year-over-year inventory.

Boston, however, remains a firm exception to these trends according to Zillow’s data. While the firm’s national home value index data had prices rising 6.3 percent in January compared with last year, to $169,600, Boston prices were up 8 percent to $351,600. And while an increase in inventory may be tempering prices on the national scale, in the Boston metropolitan area, inventory was down 11.2 percent in January compared with last year. 

Those numbers definitely put Boston in the minority among major metros. Inventory rose year-over-year in 22 of the nation’s 35 largest metro areas covered by Zillow, with the largest inventory gains coming in some of the areas that were hit hardest by the housing recession, including Las Vegas (up 42.8 percent), Phoenix (up 30.5 percent) and Sacramento (up 26 percent). These metros also experienced significant cooling in the pace of home value appreciation in January.

"Last year, tight inventory contributed to very rapid home value appreciation.  Now, more inventory is helping to moderate home value increases in many areas. This increased supply is coming from many sources, as more sellers are free to list their homes after being released from negative equity, builders continue to ramp up construction and many homeowners decide to list their homes and capitalize on recent gains," Zillow Chief Economist Stan Humphries said in a statement. "As the market shakes off a long winter and gears up for the spring season, we should see buyers gaining a bit more leverage this year than they’ve had in the past."

Zillow predicts that national home values will rise another 3.4 percent to approximately $175,301 over the next 12 months according to the Zillow Home Value Forecast.