The ocean liner-size building that just docked on North Broad Street, complete with a big glass prow to soak up the afternoon sun, does not look like the sort that helps the environment. Sprawling across 20 acres, the Convention Center is essentially a big box of meeting rooms that need to be heated and cooled. Its roof is a lifeless Sahara, devoid of vegetation or solar panels. And yet the project is on track to earn a silver award from the U.S. Green Building Council.

Somehow this does not compute.

The silver rating, third place on a scale of four, tells us at least as much about the weaknesses of the popular accreditation system - known as LEED - as it does about Philadelphia's $800 million hospitality powerhouse. Can a building that encourages thousands of airplane flights and road trips possibly be considered the least bit green?

In the macro sense, no. But on a micro level, the answer is, yes, sort of.

The creators of the LEED rating acknowledge its imperfections, but defend the system as an effective prod that has pushed building owners to reduce their carbon footprints. Energy hogs who never gave thought to the impact of solar glare (i.e., that strong afternoon sun), or the off-gassing from synthetic carpet, are now forced to confront those issues to win the building council's coveted seal of approval. LEED encourages baby steps, not revolution.

The Convention Center may rank as one of the group's great salvage efforts. Back when the Broad Street addition was being designed in 2001 - by Philadelphia's Vitetta architects and Atlanta's TVS Design - almost no thought was given to curbing electrical and water consumption, never mind limiting the use of noxious chemicals in paint and furniture. By the time the project was ready to break ground in 2008, the meeting hall still hadn't made much progress, even though competitors like Pittsburgh's David L. Lawrence Center had already slashed their energy bills 35 percent by going green. It won LEED's gold rating - in 2004.

Maybe it was the prospect of being Philadelphia's most prominent un-green building, but the Convention Center Authority did ultimately tweak its design, albeit late in the game.

The Convention Center has been stingy with details about its green accommplishments, and even declined to reveal the name of its LEED consultant. But Philadelphia is still a small town, and I was able to track down Scott Kelly, founder of Re: Vision Architecture, the Manayunk firm that coached the Convention Center to its silver rating, expected in July.

My first question: How could this dinosaur qualify for a silver rating?

Turns out, it's not that hard. LEED's certification process is like an a la carte menu. You can customize the application to emphasize your strengths, racking up points in the transit category while virtually ignoring the one for recycling.

Because the Convention Center reuses a downtown site close to mass transit, it scored big without even trying. LEED's point system favors urban sites - as well it should, since city locations enable people to get around by the lowest-energy means possible, foot and bike.

What's more, Philadelphia's 2.3 million-square-foot center purposely did not include any parking on site, to encourage conventioneers to walk from nearby hotels. The center will win more LEED points for that brave decision, even though the city Planning Commission just undermined the effort by approving a massive garage next door on Arch Street.

By today's standards for electricity consumption, Philadelphia's Convention Center just barely makes the grade. According to Kelly, the center will be 15 percent more efficient than the 2004 benchmark established by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

That's only slightly better than what the city building code requires, noted Sandy Wiggins, a former activist with the green building council and now a member of the city's Sustainability Advisory Board. "To me, that's kind of ho-hum," he added. "Certainly, it's better than where they started out. I don't want to take away from the accomplishment, but I think they could have gone further."

The energy measure may be the most crucial for the Convention Center, which must go head-to-head on price against greener halls elsewhere, particularly Sun Belt cities with lower labor costs. When the center was designed a decade ago, a gallon of gas went for only $1.50. Today, the price is more than double and rising fast, as are electric rates.

The center did better in controlling its water consumption. Kelly's firm was able to reduce the center's thirst - 40 percent better than the building code requires - by installing low-flush toilets, aerated faucets and other water-saving devices - though not the waterless urinals that have become common in other cities.

Reducing water consumption is good. Reusing the storm water that falls on your building is even better. The Convention Center does a mediocre job of capturing rain because it opted for a white roof (better than black) over a planted roof, which acts as a sponge while cooling the building.

The Convention Center did install giant cisterns in the basement to store some rainwater. That should keep a heavy surge from rushing into the city's overloaded sewer system during a big storm.

But there is no way cisterns alone can hold the thousands of gallons from even a modest storm. "Storm water control is a critical issue in the city, and it doesn't sound like they did much to mitigate the flow," Wiggins said. Most green buildings try to offset their water consumption by using rainwater to flush toilets and water plants.

Given the center's late start, it's not surprising that it remains extremely inefficient for a new building. Still, the center gets credit (and points) for embracing little things like motion lights, compact fluorescents, natural wool carpeting, green paint and natural cleaners.

The center may even make that Sahara of a roof bloom one day. Officials are seeking bids from solar panel companies interested in leasing the 20-acre plain. With all that open space, Resta estimates the Convention Center can generate three megawatts of power daily - a quarter of its peak use.

The meeting hall has come a long way since it was the Hummer of convention centers. But it's still no Prius.

Contact architecture critic Inga Saffron at 215-854-2213 or