For Rackspace, a vacant 1.2-million-square-foot '70s-era shopping mall in San Antonio wasn't a white elephant -- it was a setting fit for "The Castle," the nickname for the new green headquarters of the IT hosting and cloud computing company.

In a portion of a former tech company campus in Sonoma County, Calif., Comcast and real estate developer Codding Enterprises saw the potential for creating a "zero-carbon" operations center for the cable giant that generates no greenhouse gases from building energy.

Both projects were recently awarded certification under the U.S. Green Building Council's Leadership in Energy and Environmental Design rating and assessment standards. Rackspace earned LEED-Gold certification and Comcast attained LEED-Platinum certification, the highest ranking possible under the four-tiered green building rating system.

The firms celebrated their achievements this week, as did the state of California, which received LEED certification for the five buildings in its Franchise Tax Board campus in Sacramento. Four were awarded LEED-Gold status as existing buildings; the fifth structure, also an existing building, received LEED-Silver certification.

As green buildings, all the sites were designed to significantly reduce energy and water use compared to conventional structures of comparable size. They also use materials that are low in emissions, contribute to enhanced indoor air quality and contain recycled content. Materials- and product-sourcing as well as recycling and waste management played important roles during construction, and are the focus of robust ongoing programs at the sites.

However, planners for each project used different paths to pursue their green goals. Here's a look at some of the different environmental elements at the sites:

The Castle - Rackspace's New Headquarters

The Rackspace project, which used an approach in the building industry known as urban infill, was part of a major community redevelopment effort in San Antonio.

To achieve a LEED-Gold rating, the company's headquarters complex:

• Incorporates energy efficient lighting systems that take advantage of abundant sunshine by using skylights and lighting that can be controlled at every workstation. The system includes motion sensors and timers.
• Consumes 40 percent less water than non-green buildings of comparable size.
• Features drought resistant landscaping with an irrigation system that uses only recycled water. The water is collected in a cistern located next to the main entrance.
• Has low-flow fixtures and energy efficient hand-dryers in restrooms to reduce water consumption and use of paper products.
• Includes showers to encourage employees to bike, walk or jog to work.

During construction, Rackspace removed and recycled more than 1,600 tons of steel and other metals from the former shopping center. More than 1,900 tons of concrete, metal, wood and other materials also were recycled. And six trailer-loads of recovered, reusable building materials -- doors, windows and fixtures -- were sent to Habitat for Humanity.

Rackspace has completed two phases of renovation at the site and built out more than 230,000 square feet -- just under 20 percent -- of the available square footage.

"As our business growth dictates we will continue to develop the entire campus into our global headquarters and the tech epicenter of San Antonio," said Rackspace Director of Real Estate Randy Smith.

Next Page: Comcast's Zero-Carbon Operations Center

Images on this page courtesy of Rackspace.