A powerhouse duo on the green front

President Obama is not expected to be there. Nor is the head of Wal-Mart, Mike Duke.

But when Valley Forge building-products manufacturer CertainTeed Corp. unveils its "very, very first baby step" into the world of photovoltaic roofing next week at the International Builders Show in Las Vegas, Obama and Duke presumably will be pleased.

In the fall, each took action to inspire greater commitment to protecting natural resources and working less wastefully, known in the green vernacular as sustainability.

Obama signed an executive order requiring federal agencies to practice what the administration is urging all Americans to do to aid the environment and help build a thriving clean-energy economy: Use less energy, recycle more, and build and buy in a way that doesn't waste resources and tax the planet.

Duke, Wal-Mart's president and chief executive officer, announced a sustainability-index initiative to influence suppliers to produce and deliver their products more efficiently and with an environmental sensitivity.

Though Obama and Duke acted independently, what they did has the collective potential to significantly advance what has been a slowly evolving movement - one that draws skepticism from those who wonder whether the payoff is worth the expense.

"What you have is the 500-pound gorillas in the private sector and the public sector making these [sustainability] decisions . . . and they're going to drive the rest of the market," said Joshua M. Kaplowitz, an environmental and commercial lawyer at Drinker, Biddle & Reath L.L.P. and head of an in-house task force charged with improving the firm's sustainability efforts.

The U.S. government is the nation's single largest user of energy. It owns nearly half-a-million buildings and more than 600,000 fleet vehicles, and it buys more than half a trillion dollars' worth of goods and services each year.

Wal-Mart offers equally colossal credentials: It reported $401 billion in sales and 2.1 million employees worldwide last year.

With the federal government and one of the world's largest retailers putting their substantial heft behind the cause, the results could be a real game changer, said Shari Shapiro, an environmental law associate at Obermayer, Rebmann, Maxwell & Hippel L.L.P. in Center City.