The Evans Co. has been given the go-ahead to build a 12-story office building and a seven-story apartment building in the Route 50/I-66 corridor of the Fairfax Center area of Fairfax County.

Final development plans for the mixed-use project, to be known as One Fair Oaks, have been approved by the Fairfax County Planning Commission. That action was the final step needed to begin building the project planned near Fair Oaks Mall.

The project was known as Riverlee Springs until this week, according to Jim Evans, vice president of the Evans Co., a Tysons Corner-based firm.

The apartment building will contain 109 rental units that will be needed to support the major mixed-use commercial developments approved, or planned, for the Fairfax Center area.

"We are shooting for this fall" to start construction of the office building, Evans said. The 12-story, 200,000-square-foot building will be served by a two-level parking structure, Evans said.

The concept approved by the county at the time of rezoning allowed for possible partial underground parking.

The development will include "a central landscaped plaza in the center of the site between the office and apartment buildings," Evans said.

No date has been set for beginning construction of the apartment building. "That will be phased in," Evans said. "It will be a function of the marketplace. We are unsure of the mixture of the units." He said he expected most to be one- or two-bedroom apartments.

Designed by the McLean-based architectural firm of Davis & Carter, One Fair Oaks will be built on the west side of Ledato Road, west of Fair Oaks Mall in what the Fairfax County planning staff calls the "urban village" setting of the Fairfax Center area.

According to the rezoning approved in April, the Evans Co. will dedicate the right of way and fund portions of a future road connecting the development with Fair Oaks Mall, but the developer does not have responsibility to do off-site construction of that road.

The developer will have to donate $631 per dwelling unit and $2.83 per square foot of office space to the Fairfax County fund for future road improvements in the Fairfax Center area.

The Evans Co. project abuts the planned $325 million Centennial Gateway project, which combines residential, office and retail uses, approved by the board of supervisors last spring.