High atop the Moorish architecture of City Center, a performing arts venue in midtown Manhattan, sits a rather spectacular dome. Originally designed by architects Harry P. Knowles and Clinton & Russell, and built in 1922-1924 by the Shriners, the structure is now owned by the City of New York and sadly the condition of the dome deteriorated greatly over the years, some of the tiles had fallen off and the roof was leaking.

Earlier this year, David Paul Helpern, FAIA, and Susan Mackiw, AIA, of the New York City-based firm, Helpern Architects, in conjunction with David Ward, director of facilities at City Center, and his assistant, Peter Gates, completed a four-year project (from feasibility study to completion) to restore the dome to its original glory and once again make it a proper top hat for the building. Construction was done by Westerman Construction, with Nicholson & Galloway the general contractor.

The dome measures 104' in diameter and 50' high. The scope of the job was rather formidable: 28,475 graduated Spanish-style terra cotta tiles were manufactured by the Ludowici Tile Company of Ohio to match and replace the original tiles (also made by the same company more than 80 years ago). “The clay tiles are very unusual,” says Mackiw, the roofing specialist at Helpern Architects. “They get smaller as they get higher, with each row smaller than the one below it.” The exterior of the building has been a landmark since 1984, requiring that the same type of tile be used. There is also an intentional graduation of the colors, from light red to ochre, which adds to the beauty of the dome.

According to Mackiw, the two most daunting challenges of the restoration were fastening the tile and finding proper waterproofing. “The original system to fasten the tiles was mortar put on by trowel. In those days asbestos was used to reinforce the mortar,” she notes. This time, the more modern solution employs 23,300 linear feet of stainless steel “spider webbing” with stainless steel rods to hold the tiles (manufactured by Newport Fasteners of California) in conjunction with 8,000 power-actuated stainless steel fasteners (made by Hilti from Liechtenstein). These were actuated with a 22-caliber shot gun and the installation was supervised by a hazmat consultant. “The old system would have required 28,000 of these fasteners,” adds Mackiw.

As for the waterproofing issue, the goal was to find a membrane that would last as long as the tiles, which last up to 100 years but aren't waterproof on their own. The result was 14,000sq.ft. of 8"-thick Kemper waterproofing membrane of liquid fiberglass resin, sprayed on (complete with a 20-year warranty).

Additional work included restoration of the copper work and brass finial on the crown of the dome. “I brought some other architects from the firm to see the finished dome and they asked if we replaced the tile or restored it. It's new but looks as if it's been there since the 1920s,” says Mackiw.

“The restoration of the dome was important,” adds Helpern. “It is a unique architectural element in the cityscape and can be seen from the street as well as from adjoining buildings. City Center is a major performing arts center and it is important to preserve its architectural quality for future generations.”