Cathedral of St. John Finally Solves a 100-Year-Old Problem

It cracked. It creaked. It leaked.

Ever since the famed Spanish architect Rafael Guastavino designed the enormous dome in the early 20th century at the Cathedral Church of St. John the Divine, in the Manhattan neighborhood of Morningside Heights, it has been a source of wonder. It has also been a cause for worry and woe, requiring seemingly endless repairs.

But now, after a painstaking three-year, $17 million rehabilitation — and just in time for Christmas festivities — the dome’s 113-year-old aches and pains have been tended to. Its striking terra-cotta tile has been repaired, and a new copper exterior has been added.

“The new roofing could easily last 50 to a hundred years and there’s no reason it couldn’t last for centuries with good maintenance,” said Kevin Seymour, associate principal of Ennead, the architecture firm that was in charge of the work at the cathedral, the seat of the Episcopal diocese of New York.

Originally constructed in 1909, the dome was one of the first things built at the famously unfinished cathedral, which still lacks a south transept (an arm extending southward to complete the church’s cross-shaped plan), not to mention the remainder of the two towers on the west facade, facing Amsterdam Avenue at 112th Street. The cathedral, a concoction of Byzantine, Romanesque and Gothic styles that is the length of two football fields, making it the largest in the world, is nonetheless an official city landmark as well as a beloved New York institution and popular tourist destination.

The dome was never meant to be permanent; rather, it was a temporary topping over the crossing’s four gigantic granite arches until a spire could be erected, at which point it was to be removed.

Nonetheless, the best dome maker of the day was called in for the job: the firm of the architect Rafael Guastavino Sr. and his son, Rafael Guastavino Jr., renowned for beautiful, lightweight, durable, self-supporting vaults and arches made from thin interlocking tiles and fast-drying mortar that didn’t require external supports.

The Guastavino Fireproof Construction Company built the dome by overlapping layers of terra-cotta tiles — more layers near the base and fewer toward the (thinner) center of the dome — and binding the base with a steel tension ring. The firm completed the job in 15 weeks, including vaults below the crossing floor.

Because the dome was only provisional, however, it was never given a proper outer covering; instead, asphalt was slathered on top.

“They were always thinking that in 10 years’ time they would be building something else,” Mr. Seymour said.

The interior of the dome was similarly unadorned — what one sees, looking up from inside the church, is simply the ruddy-hued, ridged underside of the tile, a workmanlike surface unlike the smooth, cream-colored finish of tiles with decorative glazing, the kind familiar from famous Guastavino marvels around New York, like the Registry Room at Ellis Island, the Oyster Bar in Grand Central Terminal and a vaulted space under the Ed Koch Queensboro Bridge.

Still, the dome was nearly 135 feet wide, making it larger than any Guastavino’s firm had attempted before, and even today the largest of its domes. It rises to 165 feet above the crossing floor — if the Statue of Liberty was spirited uptown from New York Harbor she would fit inside.

But the project perhaps stretched even the considerable powers of the Guastavinos.

By 1916, the dome was flattening and required reinforcing with steel tension rods encased in concrete. A decade later, netting was hung below the underside of the dome to catch bits of mortar that might come loose. Then came tinkering with the pendentives, the triangular sections over the crossing arches that support the dome.

Treasured Tiles of Guastavino In New York City

They call themselves “Guastafarians” — fans of the engineering mastery of Rafael Guastavino, the Spanish architect who came to New York in 1881 with a special system for creating dramatic vaulted ceilings with terra-cotta tiles. Working with his son, Rafael Guastavino Jr., he turned New York City spaces into instant landmarks. Here are a few.

Keeping an anxious eye on it all, James Marston Fitch, the architect and preservationist who taught at nearby Columbia University, wrote in Architectural Forum in 1954 that the dome “shows signs of failure.” He warned, “even with radical and expensive surgery it cannot last much longer.”

The main problem was that the dome expanded when the sun beat down on it, warming up the materials, and contracted when they cooled at night. Seasonal weather changes compounded the problem. All the movement caused cracking. The cracks let rainwater seep in. And water crept around inside walls, causing all sorts of damage.

Insulation added in the 1970s moderated temperature swings, helping for a while.

But a waterproofing membrane installed in the 1990s eventually tore, allowing water to soak the insulation. Ultimately the dome was taking in more water than it was repelling. Ad hoc repairs would never be enough.

“We realized we had to get down to the base and start again,” said James Patterson, the cathedral’s director of facilities and capital projects.

Ennead, working with the structural engineering firm Silman, mapped out a plan. The soggy old materials were stripped away and the tile was left to dry out under loose tarps that flapped in the wind, leading to fears that they might fly off and land in Central Park.

Nicholson & Galloway, an exterior restoration contractor experienced with historical domes, repaired cracks in tiles, patched concrete, then layered on new protective materials: a hand-troweled vapor barrier, spray foam insulation, stainless-steel framing, plywood sheathing.

Topping it all is a new outer enclosure designed by Ennead and composed of slender, curved pie-shaped roof pans made of sheet copper — a material chosen to match other sections of the cathedral’s roof. Flexible seams in the new enclosure can accommodate any dome movement.

As soon as the exterior work was done, the underside of the tile was ministered to, coinciding with a cleanup in the cathedral after a 2019 fire that had left soot everywhere.

Standing on towering scaffolding erected in the crossing, a team from Building Conservation Associates, led by senior conservator Laura Buchner, gently tapped on the thousands of tiles on the bottommost layer of the dome with special plastic mallets to determine which might be loose; these were remortared. Cracked and water-damaged tiles were replaced with new ones custom-made at Sandkuhl Clay Works in Spencerville, Ohio.

Buchner was in awe of the old tilework as she examined it up close, noting how the color of the tiles selected for the center of the dome are lighter in color than the rest.

“I find it to be beautiful, all those concentric circles,” she said. “The dome may not have been intended to be permanent, but what it contributes to the overall design is very special.”

Silman attached electronic monitors to its underside to keep tabs on its temperature and any possible movement.

A new net — terra-cotta-colored so it blended in — was hung.

The roofing portion of the project, $16 million, was paid for with revenue from the sale of property to the north of the cathedral for an apartment complex, Patterson said.

Its new copper has already started to darken as it acquires a patina; it is expected to eventually turn verdigris, like the statue of angel Gabriel that has stood on the apse roof since the earliest parts of the church were built.

But even after all the care lavished on the dome, it is still considered only temporary, Mr. Patterson said. The plan remains to one day build a spire. But that won’t happen anytime soon, he added.

“We’re talking hundreds of years from now,” he said.