The Washington metro area is one of 101 U.S. housing markets that have shown “measurable improvement” for at least the past six months, according to an index released by the National Association of Home Builders Thursday. There are approximately 360 such housing markets total.

In order to make the list, a region must stay above its low point, or “trough,” in housing prices, building permits and employment for six months or more. (The low points are measured from the 2009 housing crash.) That’s harder than it might seem, because a dip in even one metric — it’s usually home prices — below the “trough” would knock a region off the list. For the Washington area, which includes the District and Northern Virginia and Maryland suburbs, the low point for jobs was February of 2010, and employment has improved 3.7 percent since then. For home prices, it was January 2011, and prices have risen 2 percent since.

The growth may seem somewhat tepid because some areas saw an improvement of 15 percent or more. NAHB senior economist Robert Denk said that’s because metropolitan Washington’s housing market didn’t fall as far as some areas did. Still, it’s a long road back to a robust housing market.

Metropolitan Washington “didn’t have it as bad as other areas, and it is improving at a healthier pace than some areas,” he said. “But it’s been a rough patch for everybody, and even the best performers are limping back to health.”

Builder permits are measured because they’re a sign of confidence among developers that things are looking up. The Washington area’s low point for builder permits was in January of 2009, and they’ve gone up 1.3 percent since then.

Denk says the improving markets counter the grim housing news that persists on a national scale.

“There’s a lot of improvement going on in tiny corners all over the country than you would glean from media horror stories,” Denk said.