The recent economic struggles, which included the failure of Seattle-based Washington Mutual, has led to an 18.5% vacancy rate in Seattle central business district.

More than one-sixth of leasable office space in greater downtown Seattle is vacant — the highest percentage in at least 20 years, brokerage Cushman & Wakefield says.

Seattle's vacancy rate hit 18.5 percent in September, climbing sharply from 14.7 percent three months earlier. The rate never has been higher since the brokerage began tracking the market in 1988, a spokeswoman said.