At 1.1 million units, Mark Zandi's 2013 housing starts forecast is more optimistic than most (the consensus forecast is about 950,000 units). But he says 5 sets of fairly simple numbers justify his bright outlook.

Set #1: At about 3.5%, the 30-year fixed rate mortgage is at its lowest point in 2 generations.

Set #2: The dollar volume of mortgage lending, while still depressed compared to historical averages, is increasing steadily.

Set #3: Housing values, after spiking at unrealistic levels between 2004 and 2008, are back to normal. (See chart #1).

Set #4: Housing supply and housing demand, which were out of whack from 2007 to 2011, are back to the long-term trendline. (See chart #2)

Set #5: 2013 will be the fourth year in a row that the U.S. economy adds at least 2 million jobs, and job growth drives housing demand and housing starts.

You do the math. Seems to add up to a better housing market to me.