Architects got slammed when the housing sector cratered. But the latest Architecture Billing Index shows they're now getting more work. The index gained for the fourth straight month, to reach its highest level since November 2007.

The thing is, architect Tom Gallas, in the Washington area, already knows things are picking up.

"We just heard today that one of our very larger projects in the Pentagon City and Crystal City areas is moving forward aggressively" says Gallas, partner of the firm Torti Gallas and partners. "This is over 700 residential units, with a Whole Foods store at the base. We're very optimistic about 2013."

When the housing economy slowed, many architecture firms got work just planning construction projects. Now, they're actually getting built.

The index finds the best part of the sector is residential -- ahead of office buildings and schools and hospitals.

"We're starting to see some stability in house prices," says economist Kermit Baker of the American Institute of Architects, which produces the index. "And I think that's pretty important. There's not too much incentive to buy a home if you think it's going to decline in value.

Ultra-low mortgage rates help, too. As far as new jobs, November saw the economy create 2,400 new architecture and engineering spots, according to the Bureau of Labor Statistics.

And despite new technology pushing out workers in other sectors, it's tricky for robots to design buildings.

"For decades I've heard the story about, you know, technology means we can be smaller and we'll need fewer employees, and we only need four architects for the whole country and that'll be good," says Doug Noble, professor of architecture at the University of Southern California. "But I don't see that in the real world."

Noble thinks the future of the industry will include lots of energy efficient buildings. Sure, the green fad has come and gone, he says, but this time seems different.