As he scampers up the tallest bit of scaffolding inside the Unitarian Church on Archdale Street, architect Glenn Keyes says matter-of-factly, "This is what you came here for."

On this upper level, some 30 feet above the church floor, is fan vaulting unlike anything else in the city.

The close-up look is possible as workers finish repairs to the church's interior. The $600,000 project comes five years after the exterior was restored.

Many think architect Frances Lee, who converted the church from its original 1787 Georgian design to a Gothic style in 1852, drew his inspiration for the tracery ceiling from the Chapel of Henry VII inside Westminster Abbey, or perhaps the St. George's Chapel at Windsor Castle.

But Paul Garbarini, a member of the church's building committee, says another possibility is the King's College Chapel, Cambridge.

"The one that really looks like us is the Carlton House, which no longer exists," he says.

Regardless of how or where Lee got the idea, his fan vaulting is considered one of the finest of its kind in the nation and a defining detail inside this National Historic Landmark.

That's why Keyes, Garbarini and committee chair Ray Setser seem happy to ascend the scaffolding and inspect it, despite the punishingly hot August air that pools around the ceiling.

Seeing the ornamental plasterwork up close is both stunning and a bit of a letdown.

It's stunning because one has to be careful walking around the stalactite-like formations, which plunge down to the very floor of the scaffolding. Our group isn't walking under the ceiling; we're walking around it, through it.

But it's also true that, seen up close, the plaster detail isn't as fine as that found inside many Charleston homes.

"It's rough. It's so far away, they didn't spend a lot of time on it," Keyes says. "From the floor, you don't see all the imperfections."

In other words, it was designed to be appreciated by the congregation far below, not by people on scaffolding.

The renovation work, funded in part by a Save America's Treasures grant and expected to be finished in a few months, mostly involved extensive plaster repair.

Keyes says conservator Frances Ford analyzed the paint and found the scheme has remained largely consistent through the years, though the new sky blue that's going back (based on evidence from 1852) will have less of a greenish tint.

The biggest surprise was the discovery of gilding on the finial tips (a design of grape clusters and acanthus leaves) and the quatrefoils -- four-leafed designs -- around the sanctuary's ceiling.

The plaster repair was extensive and perhaps just in time, given what workers discovered. The plaster along some sections of walls had pulled away from the brick by 3 inches.

Garbarini says some sections "were really defying the laws of physics."

Keyes agrees that the work fixed several problems spots that might have failed soon. "We're living good right now," he says.

Robert Behre may be reached at 937-5771 or by fax at 937-5579. His e-mail address is rbehre@postandcourier.com, and his mailing address is 134 Columbus St., Charleston, SC 29403.