Construction has begun on Sacramento's newest single-resident occupancy building downtown. On Monday, a backhoe operator and other construction workers continued demolishing an old foundation at Seventh and H streets. The eight-story, 150-unit mid-rise being built there by Mercy Housing is the first new structure going up in the railyards redevelopment project area. Once completed, the $47.4 million affordable housing project, known simply as “Seventh & H,” will be one of the city's largest permanent supportive housing projects. Half of the units will be reserved for homeless or recently homeless people, and the rest is aimed at downtown workers making $20,000 to $25,000 a year. "Sevent