NEW YORK (NYT NEWS SERVICE ).- Nobody ever said New York was a movable feast, but one rich family did its best to make it one a century ago by packing up an entire, sumptuous Fifth Avenue dining room and reassembling it in the country.

In 1927, shortly before the demolition of steel magnate Henry Phipps’ marble Renaissance mansion at 87th Street, his eldest son, John S. Phipps, salvaged its dining room’s ceiling and paneling and brought them under the roof of his grand home in Old Westbury, a colony of millionaires on Long Island.

That dining room — now featuring a family portrait by John Singer Sargent — has been a major attraction ever since in the Georgian Revival manse on the Phipps estate, which has been open to the public as Old Westbury Gardens since 1959.

But the English slate roof that shelters the room and 22 others has been a beautiful headache ever since it was installed in 1905. By 2005, the slates were in such gross disrepair that a British consultant diagnosed them in terms worthy of a medical examiner.

“He declared our roof ‘perished,’” said Lorraine Gilligan, the gardens’ director of preservation.

Restoring the roof with historically appropriate new material seemed impossible, however, until recently — when the world’s only mine producing its distinctive limestone slate reopened for the first time in half a century.

Westbury House boasts what experts believe is the only roof in the United States made of Collyweston slate, a singular material prized for centuries in England for its hardiness and for the distinctive golden yellow it turns with oxygen exposure. The slate was long employed on farmhouses and manor houses throughout Britain, as well as at Cambridge and Oxford universities.

How Westbury House came to be topped by a British stone so alien to America is a trans-Atlantic tale of successes and failures, of fabulously wealthy heirs and hardworking laborers. And the story has come full circle this year, as one of the Englishmen installing the replacement roof is the great-great-grandson of a slater who sailed from Britain in 1905 to consult on the original roof.

Both the lady of Westbury House and its designer were English. In 1903, John Phipps, known as Jay, married Margarita Grace, whose family owned the shipping line that became the Grace Steamship Co. Phipps promised to build his bride a great country house reminiscent of those in her native country.

To keep his word, he turned to London aesthete George Crawley, a passionate student of design with no formal architectural training. According to a biography by Cuthbert Headlam, Crawley had befriended Amy Phipps, Jay’s sister, while the Phipps clan was renting a manor in England.

In 1904 the Phipps patriarch, a partner of Andrew Carnegie, hired Crawley to decorate several rooms of his Manhattan mansion, including the one that was eventually transferred to Westbury House. That same year, Jay Phipps retained Crawley to design Westbury House itself.

“He was at last enabled to put into actual shape — in stone and marble, in iron and wood — the beautiful things which filled his mind,” Crawley’s biographer noted. To help him realize his vision, Crawley was paired with Grosvenor Atterbury, an architect of Gilded Age confections both on Long Island and in Manhattan.

At Old Westbury, Crawley conjured up a home of subdued, symmetrical elegance, its cherry red Virginia brick accented by cream-colored Indiana limestone and a terra-cotta cornice.

The house’s crowning glory was to be its broad-hipped roof of gold-hued Collyweston slate, a material Crawley likely knew from visits to a relative who lived near where it was mined.

The slate is made from a unique limestone found only in a narrow 3-foot seam 40 feet beneath the earth in Collyweston, a Northamptonshire village.

“Ours is the only working Collyweston slate mine in the world,” said Nigel Smith, whose company, Claude N. Smith, began producing its first new slate in 2016. “But we know from rough drawings of the area that during the 1800s peak, there were at least a dozen.”

The laborious traditional production method required three to four winters to create slates. Once mined, hunks of stone called logs were laid in a field and kept constantly wet to promote repeated freeze-thaw cycles. Eventually, the stone began to split and workers separated it into sheets of slate with a hand-forged tool known in England as a cliving hammer.

Climate change badly damaged production in the 20th century, however, by reducing the number of frosts. Builders, meanwhile, began buying cheaper, reclaimed slates from farmhouses. By the early 1970s, all the Collyweston mines were shuttered.

But as buyers like King’s College, Cambridge, emerged, Smith reopened the mine beneath the land his father had bought as a builder’s yard in the 1980s.

Technological breakthroughs made the new slating business viable. Limestone logs are now mined by a robot called the Brokk 100, and clever innovations have reduced production time from years to about a week.

Instead of relying on nature to provide the necessary frosts, Smith said, he experimented with a “lorry-back freezer,” a frozen-food truck he bought on the cheap from the Tesco supermarket chain. He now uses refrigerated steel containers designed for carrying frozen goods on ships.

Among the four workers Smith sent across the pond this year to install 37,000 new Collyweston slates at Westbury House was 26-year-old Tom Measures, a big, shy man whose baby face is covered with a rugged brown beard. It was Measures’ ancestor, Arthur Osborne, who sailed on the SS Teutonic from Liverpool with a fellow slater in 1905 to consult on the original roof.

Osborne’s services were necessary because American workers had botched the roofing job, failing to allow for air circulation around the slates and using stiff Portland cement instead of a more breathable mortar mix. Many slates also broke during shipping and installation.

This time around, Old Westbury Gardens made sure to import Collyweston artisans.

“This is a true heritage trade,” said Kurt Hirschberg, the lead designer of the roof restoration for Jan Hird Pokorny Associates, the project’s architect. The slaters perform the job in pairs, he noted, “and there’s a rhythm to the two of them working back and forth that’s amazing to see.”

On a recent frigid morning, as a bone-chilling wind sent snow flurries dancing, Measures and Conor Depellette balanced themselves on a plank supported by ladders near the ridge of the mansion’s 60-foot-high roof.

Working toward each other from opposite ends of a stretch of roof, the partners were mirror images as they moved along a horizontal wooden batten that had been nailed across the roof’s surface.

After setting a line of lime-rich mortar, each man would lay down a slate and push its bottom edge into the mortar bed until the excess oozed out like mustard from a sandwich. Then he would pick out the optimal next slate, expertly anticipating the width, thickness and texture needed to create the right functional and aesthetic relationship to both its neighboring slate and the two just below it.

When the pair met in the middle, each went along his half of the course of slates, driving a nail through a predrilled hole in the top of each slate and into a batten. The process, performed with a minimum of words, was intuitive and oddly intimate.

Later, as the pair tooled back the mortar in the slate joints to create a clean drip edge, the scraping of their trowels echoed across the countryside.

“It’s a long, long way from home, and it’s pretty surreal,” Measures said, looking out from his rooftop perch. “It’s just crazy to think I’m working on a roof one of my ancestors was working on over a hundred years ago.” Pausing to scratch his beard, he added, “It makes me feel quite proud, really.”

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