The NAHB's latest Improving Markets Index included 20 more cities.

The National Association of Home Builders (NAHB) added 20 more cities to its Improving Markets Index (IMI), further evidence that though housing remains tough in some markets, it is not only improving, but showing positive signs of growth in other markets.

Additions to the IMI included Washington, D.C., San Jose, Calif., Toledo, Ohio, Ann Arbor, Mich., and Lincoln, Neb. Bob Nielsen, the chairman of the NAHB, said the diverse nature of the improving markets is encouraging.

“The increases we continue to see in the number and geographic diversity of improving metros are quite encouraging, and evidence of the fact that all housing markets are dependent on uniquely local factors,” Nielsen said.

Created in collaboration with First American Financial Corporation, the IMI tracks housing markets throughout the country that are showing improvements in such areas as housing permits, employment and house price for six consecutive months.

David Crowe, the NAHB chief economist, also said the diverse nature of the data was cause for optimism.

“The December IMI results are very much in keeping with the latest government housing data and our own builder surveys, which have shown modest signs of improvement in certain individual markets where employment is gaining and distressed properties are not as numerous,” Crowe said. “These gradual improvements are now becoming evident not just in small, energy-producing metros that have previously dominated the IMI, but also in several larger markets and areas with more diverse economies.”

Though 20 markets were added to the IMI, nine markets were removed, namely because of small home price declines. They included  Alexandria, La., Fairbanks, Alaska and Hinesville, Ga.

For a complete listing of the 20 improving markets, click here for the NAHB press release.