The growth of several law firms in downtown New Haven helped lower the city’s vacancy rate to 13.7 percent in the third quarter, according to commercial real estate firm Colliers Dow & Condon.

Vacancy rates in New Haven in the second quarter stood at 13.9 percent, and were at 15.3 percent in the third quarter of 2007.

Most of the vacancy absorption, however, occurred in the city’s Central Business District. Vacancy in the CBD in the third quarter was 8.3 percent, compared to 20.3 percent outside the city center.

Colliers found 677,503 square feet of Class A and B space still available in the city, out of a total of more than 5 million square feet.