Source: Baltimore Metropolitan Council

As you can see, the number of permitted units bounced around but didn't really rise during the boom years. Suburban caps on building meant there were only so many new homes allowed at any one time. (The numbers above include Baltimore and its five suburbs, Anne Arundel, Baltimore Co., Carroll, Harford and Howard.)

But permitted units fell faster here than they did nationwide, even though the country saw a big increase in building during the boom. U.S. permits dropped 36 percent from 2005 to 2007, according to the federal government.

So what gives? A key reason is that homebuilders aren't just competing with each other. They've got the area's big supply of existing and rehabbed homes to contend with, too, and they want to get their own inventory under control.

I'll have a story in tomorrow's paper that looks at the ripple effects of this drop in homebuilding.