In the late 19th century, St. Paul's two leading architects were Cass Gilbert and Clarence H. Johnston. They were rivals and good friends, dating back to their days as classmates at the Massachusetts Institute of Technology.

Then something came between them — a house on Summit Avenue.

"They started to part ways as they were battling for commissions," said Ryan Knoke, an architectural historian who heads the Clarence H. Johnston Society.

The house at 701 Summit was a particular sore spot. Designed by Johnston, it was built for William Elsinger, co-founder of the Golden Rule department store. Elsinger and his business partner and brother-in-law, Jacob Dittenhofer, had decided to build big new houses side by side, and Gilbert was vying for both projects.

"He thought he had secured both," Knoke said. "Then he went out of town." While Gilbert was away, Johnston won the Elsinger commission. "Gilbert was very competitive, and that put the nail in their relationship."

The two houses were completed the same year, 1898. Both were built of Mankato-Kasota stone, but their architectural styles were in stark contrast. Gilbert's design for Dittenhofer was formal and symmetrical, while Johnston's design for Elsinger was "flowy and romantic," said Knoke, with a corner tower and off-center bay window.

This house on St. Paul's Summit Avenue was designed by architect Clarence H.Johnston. Recently restored, it will be open for public tours from noon to 4 p.m., May 13.

"If you look at both houses together, it tells you a lot about their personalities. Gilbert was stoic and serious. ... Johnston was loving and approachable."

The Johnston home also had an unusual feature — a double-sided fireplace with one hearth facing the foyer and the other on the stair landing with built-in bench. "It's something I've never seen in a Johnston house," said Knoke. "It's really spectacular."

The side-by-side homes designed by the prominent frenemies have long fascinated historians.

"These houses form one of the most intriguing duos on Summit," wrote Larry Millett in "AIA Guide to St. Paul's Summit Avenue and the Hill District."

Gilbert soon moved his practice to New York, and Johnston went on to design Glensheen, the Congdon mansion in Duluth. Elsinger lived in his grand new home for only several years, dying there in 1905 when he was just 45.

Honoring the past

Over the years, Johnston's Renaissance Revival house fell into disrepair. A recent owner tried to renovate it but became overwhelmed by the scope of work and budget required.

"It needed a lot of love — and money," said Knoke.

Last spring, the city condemned it, saying it was unfit for habitation. It was vacant when Rob Glynn of Spara Realty and Historic Hill Homes toured the rundown mansion, only a block from his own home.

"I've been in a ton of these old mansions," he said. "This one blew us away — the grandeur of the woodwork ... the unbelievable amount of detail. It needed someone to rescue it."

His firm, which has tackled other renovations, decided to restore it to its former elegance, then try to find a buyer.

Thus began the process of bringing the nearly 7,000-square-foot house up to code, with new plumbing, wiring, three new furnaces and the addition of central air conditioning. The clay tile roof, last replaced in the 1940s, also needed repair, but fortunately, the necessary tiles were already on site. "When they did the roof way back when, there was extra inventory," Glynn said.

A wood restoration specialist, Reid Rossell of Historic Oak Restoration, was brought in to revive the African mahogany and quartersawn oak woodwork, which was nicked and scratched, darkened and dulled with age. "It looked almost black," said Glynn. "Now the woodwork just glows."

The kitchen, which hadn't been updated in at least four decades, got a complete remodeling with a contemporary take. A butler's pantry had already been converted to a bathroom, so there was nothing historic left in that part of the house and "people want a modern kitchen," reasoned Glynn. In addition, the space was big enough to accommodate a modern must-have — a large, marble-topped center island.

The team also combined two bedrooms to create a second-floor master suite with a fireplace, marble bath with heated floors, and a sleeping porch.

"Somebody had brought two bedrooms down to the studs when we bought it," said Glynn, "so we had a clean slate to add a master." (There's also a two-bedroom apartment, with its own kitchen and laundry, on the third floor.)

This historic mansion, now fully restored, will be open for public tours on May 13 (details on H3).

Because the house is on the National Register of Historic Places, all exterior updates had to be approved by the Historic Preservation Commission of St. Paul. Even the mortar for the tuck-pointing had to go through several test colors, Glynn noted.

Last fall, Glynn put the house on the market while it was still being restored, intending to let a new buyer choose some of the finishes. There were interested parties, but no sale.

"We started seeing that it was too much for someone [else] to have a vision for it," he said.

Still, his team forged ahead, aided by Johnston's original architectural drawings, which were archived at the Minnesota History Center. "They were very detailed, including what species of wood was in each room," Glynn said. "We could see what had been changed."

Armed with the drawings, "questions started to answer themselves," Glynn said. "We could get in the head of Clarence Johnston and ask, 'What would he do?' We doubled the scope of the project. You can't fake it in a house like that. We were going all the way."

The most challenging aspect of the restoration was the layers of detail, Glynn said. "We had three or four tables filled with hundreds of pieces of hardware." Even the pulley system for the pocket doors had to be taken apart and put back together. "Everything works again," he said. "We wanted to reset it and get it on a new path."

Knoke hasn't been inside the house since the restoration, but he's seen detailed photos. "It looks like museum-quality [work] by real artisans," he said. "I'm really thrilled. It's what the house deserves."

Open for tour What: Public open house at a fully restored 19th-century mansion, staged with furnishings and accessories by Traditions Classic Home Furnishings. When: Noon to 4 p.m. May 13. Where: 701 Summit Av., St. Paul Cost: Free; suggested donation of $5/person will be given to Keys 4/4 Kids, a St. Paul nonprofit that provides music and art programs for children.

Rob Glynn of Spara Realty has the listing, 612-290-2941, rob@spararealty.com.