View a slideshow of the renovation

Gliding up the south side of the Philadelphia Museum of Art on platform lifts, past the tap-tap-tap of masons repointing mortar around brightly colored terra-cotta and near the oxidized-green gryphons keeping watch over the city, Gail Harrity points to the museum's four acres of cobalt and sea-green roof tiles and lets out a coo.

"Isn't that fantastic. It's a work of art," she says.

The building that houses the museum's collection may be a work of art in itself, but the main job of the building envelope is protecting the collection, and lately it hasn't been up to the task. The roof leaks. Water has poured in. Harrity, the museum's chief operating officer, says no art has been damaged. But even as it takes on an ambitious expansion, the museum is spending $31 million - more than some arts groups would spend on an entirely new home - to seal and restore its enormous limestone-clad 1920s temple on Fairmount.

Seems the entire museum is a busy if well-ordered construction zone these days. Work has begun on an underground parking garage on the west side of the main building. The $90 million Perelman annex is nearing completion, with an opening planned just after Labor Day.

And this past fall work began on the exterior of the main building, well before a Frank O. Gehry reimagination of the interior has begun. The museum's city-side face is shrouded, Christo-like, in scaffolding. From the safety of the structure, workers are repairing and replacing stone with stock from perhaps the same quarries that supplied the original stone; cleaning terra-cotta with lasers and dry ice; and replacing gutters with a new system featuring a second gutter under the first.

Preservation architects are working with art conservators from the museum's own staff to make many of the decisions.

"I think perhaps the museum views the building as the biggest object in its collection," says Michael Holleman, principal in charge from the Vitetta Group, which is overseeing the project.

After eight decades of exposure to the elements, it's time for action. The gutters were redone last in 1956, and the last repointing job was in 1976, architects say. The entire project should be done by the spring of 2009, says Harrity.

"It'll be in pretty good shape once we stop the water pouring in on all levels," she said Monday during a tour of the project.

Viewed from ground level, it's hard to appreciate the building's brilliantly colored and sometimes riotous level of detail - lion's faces lining the roof perimeter every few feet, for instance. It's equally difficult to see the decay, but a close look reveals lots to do.

A few of the enormous glazed tiles on the roof are cracked. Rub your hand along some of the limestone that encases the unseen brick structure and some of it comes off on your hand. Gilt that once covered the gryphons and other rooftop sculptures has worn away, though a fleck or two of gold can still be seen. And of course, there's water to be kept away from the priceless collection of delicate art below. After all, what good is climate control if it's raining inside?

"What this project is about is stopping water infiltration into the exterior envelope of the building," says Holleman, whose Philadelphia architecture firm has also worked on the restoration of the Academy of Music and City Hall.

What's surprising, actually, is how thoroughly the building's original architects understood the way materials would hold up over time, Holleman said.

The glaze on the trapezoid roof tiles, greenish on top and a deep blue on the sides, shows beautiful spider-webs of surface cracking, but very few must be replaced - perhaps a couple of dozen out of thousands - even if the structure beneath them has been letting in water.

"Our belief is that they are in about as good condition now as the day they went down," said Holleman.

Tiffany-designed wrought iron and bronze grillwork pieces in front of the windows were removed this week, and will be shipped to Utah for restoration.

Stone has arrived from quarries in Minnesota, one of which was the source for the building's original limestone cladding. Nan Gutterman, another Vitetta architect leading the project, says only three large pieces and about 20 smaller ones have to be replaced.

Strange to think, but even after the two-year restoration is done, the Philadelphia Museum of Art will still be incomplete. Never finished were the sculptural scenes in all of the pediments. One was done, a triangular space containing bright terra-cotta figures of Zeus and other Olympians. But seven are blank, still only brick walls.

The visual vacuum caught the attention of at least one art museum donor. A Glenside retired secretary who died in 1992 left about $1.05 million to the museum with the stipulation that it be used to "add the sculptures in any or all of the uncompleted pediments around the Philadelphia Museum of Art."

A decade and a half later, the museum does not even yet have a cost estimate for fabricating the remaining sculpture, says Harrity. One pediment, depicting wisdom, was designed for the south side, but was never built.

"Seven to go," Harrity says jokingly of the apparently fallow project.

The terra-cotta that is in place, both in the one pediment and elsewhere near the top of the building, will be restored as necessary. A few lion heads and other ornaments lining the roof perimeter are missing, says Harrity.

Not every cracked piece of terra-cotta will be replaced. If a crack is small enough the piece is neither in danger of falling down or absorbing water, it might get nothing done to it.

Sometimes the wisest preservation decision is akin to medicine.

Says Holleman: "It's like the line, 'first do no harm."

---------------------------------------------------------------------------------------------------------------------------Participating BAC1 Members:
Joe Blanche, Jack Murphy, Matt Satmary, Dan Amon, Rob Sylvester, Anthony R. Shultz, Tom Quinn,
John Quatrochi, Bob Lucchesi, Jason Burnitskie, Michael Chambers, Patrick Quinn, Matthew Corcoran, Timmy Geller, Bob Burkhardt.