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ZGF Architects has an exacting task in designing a 275,000-square-foot office expansion for California’s teacher pension system.

The building must link to an existing tower with a five-story parking structure. It must provide ample light and promote healthy choices for about 1,200 workers, and achieve net-zero energy. And it should look good from Sacramento, too.

The proposed building in West Sacramento, California, would serve as the headquarters of the California State Teachers Retirement System, known as CalSTRS. Upon completion of the expansion, CalSTRS plans to earn income on the existing tower by offering for lease approximately 200,000 square feet of space.

A photovoltaic array on the rooftop and a high-performance building envelope will combine to achieve the net-zero energy benchmark, said Kathy Berg, a partner at ZGF Architect’s Portland headquarters who is leading the design team.

About 80 percent of the building’s energy needs will be generated onsite by the photovoltaic panels. The project team is targeting LEED Platinum status from the U.S. Green Building Council.

Designers are also working to make the building present an appealing appearance when viewed from across the Sacramento River in Sacramento proper. West Sacramento is a separate municipality.

鈥淲e wanted to have a really nice composition, and not just a big tower and a mini-me,鈥� Berg said.

The expansion would reach only five stories 鈥� relatively short for such a large building. The architects considered taller designs, but decided a shorter, wider profile provided key advantages, Berg said.

鈥淥ne of the benefits of the larger floor plate is it allows the departments to have better adjacency to each other,鈥� she said. 鈥淚t also encourages the departments to have better collaboration.鈥�

The rhombus-shaped parcel also influenced the design, she said.

The expansion connects to the existing tower via a skybridge. ZGF is clustering shared amenities 鈥� such as a fitness area and tech support 鈥� near the skybridge to help unify the two-building campus.

The project prominently features a central staircase. Architects have worked to make the stairs 鈥渧isible and accessible, and pleasant to walk, to encourage people to use stairs instead of elevators,鈥� Berg said.

The building uses a concrete structure for the benefits of its thermal mass and the ability to expose the structure. The envelope is predominantly a curtain wall system, with a mix of metal panel and glazing. A perforated screen fronts the garage levels.

The design features a central atrium that will diffuse light throughout the middle of the building. Extensive glass is also used on the exterior elevations to welcome light in.

DPR Construction, based in Redwood City, California, is the general contractor through its Sacramento office. Ridge Capital, Inc. is serving as project manager.

The project is budgeted so as not to exceed $300 million. Funding will be provided through lease revenue bonds. Ground-breaking is on track for summer 2019, with occupancy to follow in mid-2021.