The average vacancy rate for Class A commercial office space in Fairfield County increased from 20.4 percent in the fourth quarter of 2011 to 21 percent in the first quarter of 2012, according to a report from commercial real estate firm Cushman & Wakefield.

According to the quarterly market report, the Stratford/Shelton submarket saw the largest increase in overall vacancy rates, rising from 8.8 percent in the first quarter of 2011 to 13.6 percent in the first quarter of 2012. That change is due in large part to the 174,000 square feet of space that came on the market when Pitney Bowes moved its operations from Shelton to Danbury.

As the vacancy rates have inched up, so too has the average rent per square foot. According to the report, the average rate in Fairfield County increased from $35.74 per square foot in the first quarter of 2011 to $36.57 per square foot in the first quarter of 2012.

Despite the increase in vacancy rates, "the investment sales market showed definite signs of improvement this quarter, with sustained increases in sales activity expected for the remainder of 2012," the commercial real estate firm emphasized.