When Justin and Samantha Barnes first saw the little midcentury pavilion in Weston, Conn., they knew it would make a fantastic weekend retreat.

The three-bedroom, three-bathroom house with its wall of floor-to-ceiling glass doors was set on a wooded two-acre lot with views of a pond. The couple, who own an advertising agency and live in Midtown Manhattan, appreciated its architectural style.

“We fell in love with it,” said Mr. Barnes, 40. “It resonated with who we are.”

Home renovations, however, are rarely simple. And the 1,747-square-foot house, listed for $795,500, was 70 years old and needed work.

The original wooden windows and French doors were rotting and fitted with drafty, single-pane glass. The radiant heating beneath the concrete floor — a cutting-edge technology in the 1940s — was nearing the end of its life. And the kitchen, updated by a previous owner, had dated granite countertops and a large column that interrupted the flow of the room.

Despite those problems, it was in livable condition. So the couple bought it in March 2017, with a vague idea of what would come next.

“We wanted it to feel very minimal and be this place where we could go to on the weekends and be creative,” Mr. Barnes said. “We got there, but it was a long journey.”

Every renovation has its own set of challenges and triumphs. What follows is the story of this particular renovation — which took nearly a year and, at $629,000, cost more than double the original budget — and how the homeowners survived it.

As Mr. Barnes said, he and Mrs. Barnes, 35, “can laugh about it now, but we were not laughing that whole year.”

The Floors

The house was built around 1948 by Edward Lloyd Flood, a young architect employed by Edward Durell Stone, the designer of a number of high-profile buildings, including the Museum of Modern Art and the United States Embassy in New Delhi, a project Mr. Flood worked on.

At the time, architects like Mr. Flood were experimenting with new ideas on small residential projects, and “Connecticut was really a center for modernist exploration in the U.S.,” said Hicks Stone, an architect and the author of “Edward Durell Stone: A Son’s Untold Story of a Legendary Architect.”

Originally, the Weston house was a single-story structure with rough-hewed pine siding and a lot of glass. But over the years, owners had expanded it with two additions, in the 1960s and the 1980s, substantially changing the footprint.

“Back in the immediate postwar era, this would have been viewed as a daring project,” Mr. Stone said, but “it’s been so brutalized.”

The floors, one of the most forward-looking aspects of the original design, were the first challenge the couple faced.

The poured-in-place concrete tiles were set in a grid of thin wooden strips aligned with the numerous door frames, establishing a geometric pattern throughout the house — “a dominant grid that controlled everything,” said Kevin Lichten, an architect the couple hired after seeing renovation plans he had drawn up for the previous owners.

Mr. Lichten suggested restoring the wood, which was deteriorating, but the homeowners wanted to replace the entire floor with a single plane of concrete — with no sheen or seams.

But replacing the floor would be a huge undertaking, requiring jackhammers to dislodge the concrete tiles, some of them 10 inches thick.

They considered skim-coating the floor instead, or installing new material on top of it. But with seven-foot ceilings, they didn’t have a lot of height to spare.

There was another problem, as well.

Beneath the floor lay a 70-year-old radiant-heating system made of copper pipes filled with water, which, when heated, warmed the concrete floor and the house, a technology that was relatively new in the United States at the time it was installed.

But because concrete reacts with copper, the contractor, Hugh Bilecky of Caperton Company, suspected that this particular system had, at most, five years left in its life. Already, some zones in the house no longer worked.

The new system would consist of a grid of plastic tubes set on top of a layer of foam insulation, with a vapor barrier and steel reinforcement mesh. Once the floors were removed, there would be an opportunity to install a new central air-conditioning system, too.

It was an investment that made sense, but it came at a steep price: $37,000 to demolish and replace the concrete, $30,000 for new radiant heating and another $30,000 for central air. And “the demolition for that was a nightmare,” said Shane Reidy, the associate architect who oversaw the project.

Replacing the concrete wasn’t easy, either.

The couple wanted a single sheet of concrete, but the risk was that, without seams, it might crack.

They also wanted a matte finish with no discoloration, but concrete sealants are usually made of polyurethane, and tend to yellow over time. Leave the floors unsealed, however, and the surface would be dusty and stain easily.

“You spill a glass of wine,” Mr. Barnes said, “and it’s over.”

Mr. Reidy found a manufacturer who made a sealant that would give the homeowners the matte finish they wanted, but when the floors were ready to be poured in April 2018, neither of the local vendors could get the sealant in time. Not wanting to throw off the schedule by delaying the installation, Mr. Reidy scrambled to find an alternative sealant that could be applied after the concrete cured.

For his part, Mr. Bilecky had to make sure the workers laid the concrete precisely — in a single 15-hour day — because it needed to be flawless.

“I told them, ‘It’s a one-shot deal — this is the finish,’” Mr. Bilecky said. “It’s not like it’s going to be covered with carpet or tile.”

Somehow a footprint ended up on the surface. It not only had to be removed, but Mr. Reidy also had to find a new sealant that would give the homeowners the matte finish they wanted without reacting to the cleaning agent Mr. Bilecky used to remove the mark.

The new floors, however, transformed the feeling of the house.

“A lot of people would think the house feels cold and sterile and Brutalist,” Mr. Barnes said. “But when you warm it up, all that changes.”

What they learned: “Don’t count your chickens,” Mr. Reidy said, recalling the stress of racing against the clock of drying concrete to find an alternate sealant. If you see a material that you love, order it. What’s on the shelves one day could be gone by the time you need it.

A Room with a View

Before the Barneses began the renovation, their architect gave them a piece of advice: Live in the house first, to see how you use it.

They discovered that they used the first-floor den (formerly the second bedroom) as a television room, but with a French door facing the front and one side of the room nearly all glass, the glare from the sun made it hard to watch TV. The layout also left few places for furniture.

They weren’t happy with the mudroom, a bare-bones addition by a previous owner that felt more like a screened patio than part of the house.

And then there was the problem of the glass doors. The series of angled French doors along the living room wall gave the exterior an accordionlike appearance. Originally, they all would have opened, turning the living-and-dining area into an outdoor pavilion.

“They are unique in the way that they undulate,” Mr. Reidy said. “Most doors don’t do that.”

But by 2017, few of them were operable, and the single-paned glass made the house drafty and cold. They needed to be updated, but the homeowners did not want to sacrifice character for comfort.

“That’s the whole reason for the house — it’s those windows,” Mr. Barnes said.

But after spending a summer there, they decided they did not need to be quite so open to the outdoors, as New England summers are hot and buggy. And with so many doors, guests often didn’t know which was the main entrance.

So the couple decided to replace the undulating French doors with a wall of fixed glass doors, with only one opening to the front. They created a more formal entryway by renovating the mudroom, installing insulation, a proper foundation and a wooden front door, painted black.

Replacing the original French doors, which had likely been built on site, with similar ones wasn’t an option: The homeowners wanted as much glass as possible, and wood frames tend to be wider.

They decided on steel, which would be strong, maximizing the area of glass and giving the house the minimalist aesthetic they wanted. But it wasn’t cheap. Fitting the entire house with steel-framed windows and glass doors would cost $160,000, a price that came as a shock.

“We were surprised at everything,” Mr. Barnes said. “Why are windows so much money?”

The architects suggested an alternative: aluminum, for half the price. But aluminum isn’t as strong as steel, so most of their options had thicker frames, cutting down on the size of the glass. Finally, they found a manufacturer in upstate New York that made aluminum windows with thin frames, but the double-paned glass had to be ordered from a different company.

The look, while close to the couple’s vision, was not exactly what they had in mind. “We love them, and it looks amazing,” Mr. Barnes said, but with steel, “it could have looked more amazing.”

To reduce the light streaming into the den, Mr. Lichten removed a French door that opened onto the deck, replacing it with a transom window, adding to a row of transoms along the top of the wall. This also created a place to put the television and made the room cozier.

The architects replaced the wall of undulating French doors on the side of the house with the new doors, limiting and focusing the view of the property. They also opened views across the house by removing a partial wall that obstructed the view from the den across the living room.

The original design, with its abundance of windows, Mr. Lichten noted, was similar to a Richard Meier house made almost entirely of glass: “It’s beautiful, but how do you sit there and read when you have this infinite view? A lot of this was about controlling the views.”

What they learned: Not all compromises are worthwhile. At the time, $160,000 seemed like a staggering price tag for steel doors, but looking back on it, the Barneses regret their decision. “We should have spent the money on the steel,” Mr. Barnes said. “It would have looked way better.” But in the middle of the project, they were so worried about the budget that it was hard to see the importance of that particular design element.

Keeping the Water Out

Midcentury modernism attempts to erase the boundary between indoors and out, so that a house blends into the landscape around it, like Philip Johnson’s Glass House in New Canaan, Conn., built around the same time as the Weston pavilion. But nature is not always forgiving, and no homeowner wants the outside to come rushing in during a storm.

“When people naïvely buy midcentury-modern houses, they don’t realize that they come with all these inherent technical challenges, like a flat roof,” Mr. Lichten said.

This particular flat roof needed some patchwork, but otherwise did not leak, although it had no gutters or downspouts to interrupt the design’s clean lines; instead, rainwater traveled through cutouts in the roof, down chain-link rain chains into the ground.

Without a raised foundation, the floor-to-ceiling glass came all the way down to the slab, increasing the risk that water could seep in if snow or ice built up over a long winter. So when the architects replaced the original glass doors, they set the new sills in a bed of silicone caulk on top of the foundation wall to keep water out.

There was just one major water problem: The house was built against a rocky hill, so rainwater traveled down the rocks and around the back. A previous owner had built a trench along the base of the hill to redirect water. But after the contractors removed the floor in the kitchen, which faced the hill, they discovered the fix hadn’t worked.

The following morning, after a heavy rainstorm, Mr. Bilecky, the contractor, arrived to discover more than a foot of water in the kitchen. “It was pouring off the mountain,” he said.

A concrete floor at grade level is naturally prone to water problems: If it’s cool at night, water beneath the slab freezes and expands; in the morning, condensation can seep up from below. “You could literally have puddles on the floors,” Mr. Lichten said — even without the challenge of having a waterfall on site.

Before a new floor could be laid or radiant heating installed, the contractors had to get the water out and divert incoming water away from the house. The lot was too steep and narrow to bring in heavy machinery, so workers had to create a gravity drainage system by hand. The crew dug a trench inside the house and around the back, cutting through six feet of stone and digging under a tree, to run drainage pipes down the hill.

That delayed the renovation and added $17,000 to the cost.

“Everything was put on hold for three weeks while we resolved the water problem,” Mr. Bilecky said. “It was tough going.”

With that water problem solved, the only one that remains is acoustic: Thanks to the flat roof, and no attic to buffer the noise, the sound of rain coming down can be distracting.

“When it rains, it’s so loud,” Mrs. Barnes said. “After 12 hours of rain, you have to go out or you’ll go completely insane. It’s unreal.”

The couple considered installing a green roof, but the structure is not strong enough to hold one, Mr. Lichten said. So for now, they live with the sound of the outside coming in.

What they learned: Plan for the unexpected, because walls, ceilings and floors can hide trouble. Before the construction crew removed the concrete floor, they drilled exploratory holes, looking for potential problems, but didn’t find any evidence of water. It was only later that they discovered the problem. Homeowners should allow for a flexible timeline — and extra money in the budget — to deal with unpleasant surprises like that.

A Chef’s Kitchen in a Small Space

Mrs. Barnes, who studied cooking in Florence and was an owner of a farm-to-table restaurant in the Hudson Valley until 2015, had strong opinions about the kitchen.

“Coming from the restaurant world, and my time in Italy, I knew I wanted a simple and efficient working layout that would be durable and stain-resistant, like a restaurant kitchen,” she said. But she also wanted it to be comfortable and inviting, so she could entertain while she cooked.

To reduce costs, she and Mr. Barnes hired a local kitchen contractor, rather than using the architect and general contractor, and spent about $75,000.

They wanted the kitchen to have a matte, muted finish, like the rest of the house, with clean lines and a minimalist look. “Basically, we wanted the kitchen to look simple and clean on the outside, while having high-end appliances and everything we need hidden,” said Mrs. Barnes, who had a long list of appliances she wanted, including a Wolf stove, Sub-Zero refrigerator and a Holcomb sink in black quartz composite.

Another must-have was an oversized island. The old kitchen had a dated granite island, partially enclosed by a column that housed the washer and dryer on one side and an oven on the other. After removing the column there was enough extra room that “we literally got the biggest piece of Caesarstone we could get,” Mr. Barnes said.

The slab — 51 by 105 inches — was delivered on a flatbed truck and hoisted into the house with a crane. But the full-sized slab was polished, not the matte finish they had selected.

“It was a big deal,” Mr. Barnes said. “We were tired of making compromises. We didn’t want a big piece of shiny countertop.”

So the slab, which had already been installed on the island, was removed, taken back to the factory, honed and reinstalled a week later.

The couple chose Miralis cabinets in a black satin-matte finish, without hardware; the drawers, cabinets and Miele dishwasher open by touch.

The downside? Lean against a wall or the island, and a drawer is likely to pop open.

“The kitchen looks great, but I wish we’d been a little more thoughtful about functionality,” Mr. Barnes said.

There are no overhead cabinets or pantry, which gives the room a clean look, but not much space to store food.

“A lot of people would look at that kitchen and say there’s no pantry or storage,” Mr. Barnes said. “We go out to dinner a lot, or just buy food to eat that night. We don’t have kids, so there’s no food in the house. We keep everything very simple.”

What they learned: When you’re renovating a kitchen, prioritize function. A kitchen has to work well, not just look pretty. The Barneses focused so much on aesthetics that they overlooked practical considerations, like minimalist cabinet doors that open when you don’t want them to — because you lean on them. “Everyone was advising us against them,” Mr. Barnes said. “In the end, they were right.”

Nowhere to Hide

Most homes have attics or basements or, at the very least, enclosed ceilings and closets — places to hide what you need but don’t want to see, like hot-water heaters and ductwork. But the Weston house is basically a box sitting on the ground, with an open ceiling of exposed trusses and beams.

“The problem with a modern pavilion is it wants to sit like a beautiful object on a plane, which makes it really hard for the practicalities of living,” Mr. Lichten said.

And in their quest for a stripped-down aesthetic, the homeowners did not make that situation any easier.

They didn’t want cabinets in the kitchen or extra closets. They didn’t want visible outlets. In the kitchen, they replaced a large pantry with a blank wall.

Without an enclosed ceiling, there was no way to install an overhead light fixture. So the architects installed tiny track lighting along the beams, hiding the voltage transformers in the few closets the house did have. Vents for air-conditioning were tucked between the trusses in the ceilings and returns were built into the floor.

The tiny mechanical closet is only three by six feet, yet it houses a combination hot-water-heater-and-boiler, an air handler and an electrical panel. When the electricians and plumbers came, Mr. Bilecky, the contractor, gave strict orders that measurements had to be exact within a half an inch. “There was a huge amount of work to get all the plumbing in that little closet,” he said.

The homeowners also needed a place for the washer and dryer, as the column that housed them had been removed. So the architects turned one of two full bathrooms on the first floor into a half bathroom with a closet for the washer and dryer.

In the kitchen, outlets were tucked behind drawer panels, in place of storage. “I think they thought we were a little crazy,” Mr. Barnes said. “A lot of times people are thinking about functionality, but we were thinking about aesthetics.”

What they learned: Hire a knowledgeable team. Figuring out how to add luxuries like central air-conditioning to a house with so little storage space would probably not have been possible without a creative architect. “That’s where the architects are really shining on this project,” Mr. Barnes said.

Decorating a Midcentury Space

The couple began collecting art about six years ago, amassing a collection that includes works by Damien Hirst, Ai Weiwei and Joan Miró. And many of the decisions they made — from the light gray walls to the tiny track lights — were to highlight the art.

“The No. 1 consideration for everything was making space for art,” Mr. Barnes said.

But a house with so many windows creates a couple of problems for art collectors: Wall space is limited, and the glare from natural light can damage the artwork and make it hard to look at.

A large black etching by Richard Serra, for example, hangs on the back wall of the dining room, where light bounces off it, despite the non-reflective glass used to frame it. “There is no amount of non-reflective glass that can stop that,” Mr. Barnes said.

The homeowners spent months visiting furniture stores, searching for dark, low-slung pieces that wouldn’t compete with the art and would work with their low ceilings. Some of the furniture, like the credenza in the dining room beneath the Richard Serra, were chosen specifically to complement the art.

“We took the floor plans and measurements of everything and laid it out 100 different ways in Photoshop,” Mr. Barnes said. “We were pretty meticulous.”

For the living room, they ordered a 12-foot Mondrian sofa from Poliform, pairing it with an Eames chair. For the dining room, they bought a large matte-black table and Eames dining chairs.

Getting the furniture into the house wasn’t easy, either.

The spiral staircase to the master bedroom is too narrow to fit anything larger than a laundry basket, so the bedroom furniture and a “huge piece” by the graphic designer Paula Scher had to be hoisted up to the second story on a ladder.

“We might just leave it there if we move,” Mr. Barnes said of the Paula Scher work. “I don’t know.”

What they learned: Consult an interior designer. The couple decorated the house themselves, but in hindsight, they wish they had hired a professional to offer guidance. When they chose the fixed doors for the living room, for example, they failed to consider what sort of curtains might work with the new doors, and they still haven’t hung any. As Mrs. Barnes put it, an interior designer “can help think about the end product a little bit more clearly than you can.”

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