The United Nations executives leading the $2.1-billion renovation of the U.N. headquarters on Manhattan's far East Side are known for commanding military-style control over the high-profile, closely scrutinized project. The approach seems to be working.

The project's leaders, charged with overhauling 2.5 million sq ft of space within an active 17-acre campus, have about one year to go on the six-year project. To date, though the work is 12% over budget, they have managed to keep a low profile and avoid major disruption to regular U.N. activities. Crews tiptoe around as many as 4,800 U.N. staff within a compound that, since 2008, has been annually hosting 8,000 conferences and one million visitors.

"The U.N. renovation is the most challenging project I've ever worked on," says Michael Adlerstein, executive director of the U.N.'s capital master-plan (CMP) department, which is responsible for the work.

Adlerstein's team also has to manage myriad designers, the construction manager's 23 guaranteed-maximum-price (GMP) contracts and the 659 trade contracts as well as the 900 peak daily workers executing the phased subprojects. As part of the international organization, the CMP must follow U.N. practice, which means complying with strict rules for reporting progress to the 193 member states funding the project through assessments.

Adlerstein, an architect who managed the centennial restoration of the Statue of Liberty for the U.S. National Park Service, has a very hands-on style. He not only runs the 26-person CMP, he informally functions as the renovation's master architect, reviewing and approving everything from the mechanical room's layout to curtain-wall replacement glass.

True to its crisis-avoidance culture, last Oct. 25, when Superstorm Sandy was coming, the CMP set in motion its meticulously plotted emergency weather plan. But five days of maneuvers, including battening down the hatches with sandbags, did little to stem Sandy's tide.

On Oct. 29, Adlerstein and his deputy, Kenneth Champion—on campus with the storm's ride-out team—slogged helplessly through two feet of water as the East River invaded 350,000 sq ft of newly renovated basement space. The chiller plant filled up like a swimming pool, drowning the equipment in nine feet of water.

It could have been worse. The campus-wide basement consists of three full-footprint levels above two rooms: the 4B chiller plant and the 5B pump room. The storm surge, which mainly breached the 3B loading dock off an underground service drive, also drowned the pumps. While the water was two to five feet deep on 3B, the two upper levels and the data center were spared.

"Despite the severity of the unprecedented storm and flooding, material damages in the U.N. compound were relatively contained as a result of effective precautionary measures," says Champion, the CMP's program director.

Even so, the repair tab, still under assessment, is "tens of millions of dollars," says Adlerstein. Project sources say it could reach $100 million.