Clark County’s free-falling housing prices may have actually hit bottom over the winter and started a slow ascent in March, due to stronger demand for mid-range to upper-end houses.The demand, coming mainly from the employees of newly relocated companies such as PeaceHealth and Fisher Investments, likely contributed to a 6.7 percent increase in county home values in March compared with February’s prices, according to Terry Wollam, an agent with Re/Max Equity Group in Vancouver. He also cited a shrinking supply of houses listed for sale. Others say rising rents, growing consumer confidence and improvements in household budgets could help finally strengthen the housing market.There are caution flags: National housing analysts warn that the market still could be flooded by a “shadow inventory” of bank-owned houses and units that have not yet been vacated by delinquent owners.In Clark County, the median home price — half sold for more, half for less — was $176,000 for houses sold by licensed real estate agents in March, according to Portland-based RMLS. That price has risen slightly compared with recent months, after a period of relative stability that began in mid-2011.“That’s when we started to see it (the median price) level out,” Wollam said.Now, he and other real estate brokers expect housing prices to rise, based on rising demand and a shrinking supply of houses listed for sale in Clark County. At the lowest level since September 2006, it would take just 6.4 months to sell off the inventory of housing units listed on the market if no new listings were added, RMLS reported.