Having already developed dozens of projects for other companies with an eye on sustainable development, Opus Northwest is going green in its own back yard with an expansion of its headquarters in Minnetonka.

The Minnetonka-based developer has set its sights on having the project certified by the nonprofit U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) building program. Established in 2000, the LEED system rates buildings in a variety of areas, including water and energy conservation, use of recycled or environmentally friendly materials and indoor quality.

The number of LEED-certfied buildings nationwide has jumped from 38 in 2002 to more than 1,500 so far this year, according to the council, based in Washington, D.C.

Minnesota has 14 certified commercial projects, up from just four a year ago, while the number of developments seeking certification has grown to more than 170.

In Minnesota Opus is pursuing LEED certification for the Excelsior Crossings office complex in Hopkins and new office buildings in Minnetonka for Syngenta Seeds and UnitedHealth Group.

"Virtually all our new speculative projects are geared toward sustainable development," said Opus Senior Vice President Tim Murnane. "We decided that with our own building it was important for us to walk the walk."

Work on the 148,000-square-foot building, made in part with recycled construction materials, has been going on for several months. Other environmentally friendly features include the use of low-vapor paints, adhesives and sealants, and high-performance glazing and glass to maximize energy efficiency.

But work on perhaps the most ambitious energy-saving feature of the building just began. Earlier this month two rigs began the task of drilling 299 wells, each about 185 feet deep, on the land surrounding the new building. The wells are part of a geothermal system that will use the relatively constant temperature of the ground to heat and cool the building.