Penny-pinching real estate investment trusts are increasingly looking to splurge on Earth-friendly designs as they try to corner environmental-minded tenants.

Duke Realty wants to include features such as sun shields, a bicycle storage room with showers (to encourage workers to use cars less) and motion-detecting faucets in Regency Creek I, a planned Cary office building. The features could push construction costs 10 percent above those of traditional offices, and that could boost rents about $1.50 per square foot.

Jeff Sheehan, Duke's top Triangle executive, isn't afraid of losing a pricing edge. "It's a selling point," he said. "And it's the right thing to do. There are tenants willing to pay for it; there are some who could care less. But as more ask for it, the more the development community will move towards it."

It's the latest sign that green-building, long a fringe niche in the profit-driven development world, has hit the mainstream.

In 2000, the U.S. Green Building Council established the Leadership in Energy and Environmental Design rating system to promote Earth-friendly and energy-efficient construction. Developers earn points by incorporating features such as systems that conserve water and electricity and reduce dependence on heating and air conditioning.

Building green can be more expensive, as Regency Creek shows. That's why institutional owners such as government agencies and universities, which tend to own and occupy buildings for decades, have been more willing to take the plunge. They are more focused on operating costs. A 100,000-square-foot building without sustainable-design features might cost about $30 million to operate over 40 years, according to architecture firm SFL&A. The same building with about $3.5 million in green design features could save the operator $8 million in utility costs over the same period, based on current energy prices.

Real estate investment trusts make money by leasing buildings, not occupying them. That's why they focus on construction costs. The lower the costs are, the easier it is to keep rents lower than competitors, but high enough to generate the income that shareholders expect.

Duke's building, to be finished in early 2008, could be the Triangle's first REIT-built, LEED-certified project. That's if Highwoods Properties, which also has mulled LEED certification locally, doesn't beat it to the punch.

Duke might also decide to skip certification, saving tens of thousands of dollars, Sheehan says, adding: "The important thing is having the green sensitivity."

Another penny pinched.