Iron Bridge LLC, of Spokane, expects to start construction this fall on two new connected buildings valued at up to $20 million at the Iron Bridge Office Campus along the Spokane River east of downtown, says Kent Hull, the company's managing partner.

Hull says the company plans to begin construction shortly after it finalizes lease agreements with two large prospective tenants.

"We anticipate having leases signed by the end of summer," he says, adding that work at the project site would then start in September or October.

The planned buildings, named Iron Bridge IV and Iron Bridge V, would more than double the office space in four buildings already developed at the 21-acre corporate park headquartered at 714 N. Iron Bridge Way, just north of Trent Avenue, Hull says

"They will have three stories and a total of 179,000 square feet," he says of the planned structures.

Hull says the tenants the developers expect to sign will take up most or all of the space in the two buildings.

The campus currently has a total of 165,500 square feet of office space in four buildings, he says. Iron Bridge LLC has developed three of the buildings there between 2003 and 2009. The company also developed a four-level, 555-stall parking garage near the center of the campus in 2008.

More recently, Iron Bridge LLC, bought a 100-year-old building, now named Iron Bridge VI, on the southwest portion of the campus and remodeled the three-story former residential condominium for office use last year.

Ron Joseph Architecture, of Spokane, designed the planned buildings. Hull hasn't named a contractor for the buildings yet. Divcon Inc., of Spokane Valley, has erected three office buildings and the parking garage there.

The buildings will be connected by a center atrium that will face the century-old iron-truss bridge that's the namesake of the corporate campus, Hull says.

The bridge, which spans the Spokane River west of the campus, was built in 1911 by the Oregon & Washington Railroad & Navigation Co., according to the Rails to Trails Conservancy website.

The railroad line, which served mining areas in North Idaho's Silver Valley and the northern Bitterroot Mountains in Montana, closed in 1973 during preparations for the Expo '74 World's Fair, in Spokane.

Last year, the city of Spokane converted the abandoned 560-foot-long, three-section bridge to a pedestrian bridge to connect to nearby trail systems, including the Centennial Trail, which passes by the west end of the bridge.

Iron Bridge IV and V will feature a concrete, brick, and glass exterior that will complement other buildings on the campus, Hull says, adding that a pedestrian sky bridge will connect one of the buildings to the parking garage.

Hull says the Iron Bridge Office Campus has been nearly fully leased for the last three years. Mike Livingston, of the Spokane-based commercial real estate brokerage Kiemle & Hagood Co., is the leasing agent.

Tenants at the campus include Pathology Associates Medical Laboratories LLC, State Farm Insurance Co., the Social Security Administration, and HDR Engineering Inc.