The clients didnt want it to feel as if they had inherited their grandmothers apartment, designer Christine Gachot remembers thinking at the outset of a top-down renovation of an Upper East Side prewar duplex for a couple with four young children. Having relocated to uptown Manhattan from Tribeca, they wanted something fresh, but they did want to keep some of that traditional sensibility.Christinewho, alongside her husband, John Gachot, runs the namesake firm noted for dreamy, cinematic interiors that blend contemporary and classic elementsknew at once they could deliver what the homeowners had in mind. Spread over two floors in a 1907 American Beaux Arts building by Delano & Aldrich, the residence had ample space, but, says John, it had really been lived in, chopped up, and adapted for the previous owner. Poring over original floor plans from the building and similar edifices nearby, the designers were able to craft a layout that would feel original but could perform as a forever home for this growing family.The living room of an Upper East Side duplex gut-renovated by John and Christine Gachot, of NYC-based firm Gachot, alongside general contractor Fiocchi Group, for a discerning couple with four young children, blends comfort with old-world elegance. Pastellone plaster walls painted in Benjamin Moores White Dove, ornamental moldings, and an Arabescato mantel from Jamb provide a subdued envelope for a mix of vintage and custom furnishings. The Gunnel Nyman club chairs, sourced by Hostler Burrows, wear a cream wool from ALT for Living and complement the bespoke sofas wrapped in nutmeg mohair from Angela Brown LTD. The round marble-and-brass coffee table was also designed by Gachot. Illuminating the space after sunset are circa-1940 floor lamps by Lysberg and Hansen, sourced by Jackson Design, and a double-silk ceiling fixture from Gong.Architecturally, the aim was to carve out spaces that would adapt with the familys changing needs over time. The apartments working wood-burning fireplaces would become the focal points for the homes public areas downstairs, in what would ultimately become the living room and den. Fortunately, the expansive living room could comfortably accommodate a formal dining table for eight or more, which allowed the owners to transform the former dining room into a sunny breakfast/play area adjacent to the kitchen.Upstairs, on the more private level, one of the abodes six bedrooms was turned into a secondary playroom for toys and books. And, in an especially ingenious gesture, a mudroom for stroller parking was created adjacent to that floors entry in such a way that it could one day be converted into a home gym or office. Phases of life change, so those spaces need to be able to adapt to tweens, teenagers, and then eventually to making closets bigger, explains John. There are these little adjacencies we planned on.The sunny kitchen was designed to be both traditional in appearance and highly functional. The millwork, painted in Benjamin Moores Shadow Gray, oak-herringbone floors by J. Rapaport Wood Flooring, and subtle marble with delicate veining create a soothing atmosphere at any time of day. Waterworks fixtures, RW Guild ceiling fixtures, and Simonini counter stools complete the look. This felt like it could architecturally have fit into that original apartment with a few updates, observes John of the family hub.The breakfast room is the locale of casual family meals and gatherings throughout the day. A custom ceiling light by Gachot and Scandinavian sconces sourced by Bloomberry cast a warm light on the Dedar-covered built-in banquette, oak table by Alfred Newall, and Freda Razor dining chairs by Hati Home. Its kind of the old Parisian apartment trick, says Christine. You put modern furniture in a traditional backdrop and it somehow just looks perfect every time.With the core structural plan in place, the Gachots took the same evolutionary approach to the interior decoration, creating a timeless backdrop for future chapters. They gave traditional architectural detailsplaster walls, crown moldings, baseboards, marble mantels, and trimsa delicate update with profiles, proportions, and finishes that feel clean and refined. Theres so much room for them to add their own layer, says Christine of the brief. When you are looking at a young family, they have a long way to go of collections and travels and experiences that will only add to the breadth of the home. The library, lined in solid white oak, smacks of old-world Manhattan, but its custom sectional and Milo Baughman tub chair, all covered in mohair, are conducive to kicking back on movie nights. Even the formal living room pairs rare piecesa rosewood-and-mahogany cabinet from the 1930s, Gunnel Nyman club chairs, a Fantasia coffee table by Philip and Kelvin LaVernewith durable, plush custom seating and airy double-silk ceiling light fixtures. The timeless English-inspired kitchen, aglow with light bouncing off of subtle marble counters, light-gray walls, and oak-herringbone floors, retains a crisp, New Yorkcentric efficiency.In lieu of having a grand staircase, the team elected to maximize usable space elsewhere. Here, in the upstairs landing, illuminated by a brass-and-silk ceiling fixture designed by Gachot, a mahogany handrail, bronze stair spindles, and stained oak-parquet floors emphasize the apartments timeless quality. On the wall, Jim Shaws The Land of the Octopus 6, adds color and movement.The familys art, too, plays a crucial role in this story of evolution, finding the sweet spot between old and new. Working with personal art consultant Anne Bruder, the Gachots and their clients added another layer of meaningful personality with thoughtfully placed pieces: a textured Dan Colen canvas in the entry hall, serene pieces by Louise Lawler and Katherine Bradford in the living room, and colorful Jim Shaw works in the upstairs landing and primary bedroom. In a home built for change, that latter serene, expanded hideawaywith its walls wrapped in creamy Dedar silk, 1940s club chairs wearing a jaunty yellow Sahco pattern, and Pinch bed covered in a natural C&C Milano fabricis perhaps the only area intentionally given a more permanent, anchored vibe.The clients knew what they liked, and thats really half the battle, says Christine, who, a fellow parent of young children and also a recent downtown-to-uptown transplant, felt particularly close to this project. If you have people that are willing participants and come with knowledge, theyre sitting at the table with you, and its lovely. Reflecting on the process, John nods in agreement: Youre producing their movie.It was a real treat to walk in and be like, Yes, this place is amazingI can do something, John remembers thinking when first visiting the apartment pre-renovation. Here, the team carved out a formal dining area in a space between the commodious living room and den. The expandable custom table, designed by Gachot and fabricated by Fischer Furniture, is surrounded by rosewood dining chairs from Modernity covered in fabric by Prelle. The 1960s brutalist credenza from Spain, sourced by Morentz, is topped by a French crystal lamp from Danke Galerie and an Art Deco coffee and tea set found at Maison Gerard.The building is iconic and beautiful, shares Christine of the venerable address. Its [built to have] room after room of discovery. The oak-paneled library strikes a more traditional note while plush furnishingsincluding a custom sectional sofa covered in moss Marci mohair and swivel tub chair by Milo Baughman in Holland & Sherrys Rive Gauche mohairencourage casually kicking back. The space is illuminated by a circa-1946 floor lamp from Ponce Berga, custom double-silk ceiling fixture by Gachot, and Modulightor picture lights. A side table in the form of a Gunnera leaf by Cox London, custom coffee table by Gachot, and elephant-shaped storage box by Pamela Weir-Quiton stand on a custom area rug by VandenLoom.The idea was to give [the clients] their own little sanctuary, John says of the serene primary bedroom with its own seating area. If the nanny is spending the night, they can close the door and have their suite to themselves and not be disturbed. On one end of the room, a Moreau bed by Pinch is covered in a custom Charvet linen bedspread and flanked by maple-and-brass tables by Tommi Parzinger, sourced by Donzella. The lamps are 1950s Murano Sommerso, sourced on 1stDibs. A pair of 1940s club chairs covered in a patterned silk by Sahco and sourced by H. Gallery populates the other end of this space. The drapery is cut from an ivory Holland & Sherry wool.A view into the wifes own bathroom, where Imperial Danby from Beata & Agnes Stone Gallery and the Venetian plaster walls and ceiling enhance a sense of peace. The unlacquered Waterworks fixtures complement the Scandinavian ceiling fixture, sourced by Bloomberry, and Mr. Shower Door frame. The oak-and-leather stool, meanwhile, is from Nickey Kehoe.Another girls bedroom demonstrates how the Gachots thoughtfully maximized storage throughout; even the bed is tucked into a niche to make room for a built-in bookcase in the threshold leading to a shared bathroom. The wallpaper, by Helen Blanche, was sourced from Temple Studio, while the Pinch bed is covered in a linen fabric from Designs of the Time. Samuel & Sons tassels hang from cabinet pulls from the Brass Center.The girls rooms are as cute as crackers, says Christine. Theyre just so charming. In the twins domain, the Gachots, known for their penchant for calm interiors, answered the homeowners call for a dose of pattern by covering the walls and beds, fabricated by Charles H. Beckley, in a delicate floral print from Peony & Sage. A 1960s glass lamp with pleated shades by Lamptouch adorns a dresser from Trove by Studio Duggan beside a burl-wood table sourced on 1stDibs. The striped Roman shade wears a fabric from Soane Britain.In a downstairs powder room, a hand-painted gold-and-blue silk wallpaper by Fromental adds whimsy surrounding the custom St. Laurentmarble sink from Novo Marble. Waterworks fixtures, an Alix D. Reynis sconce, and mirror by Soyun K. round out the transportive space.