For her family's mountain house in Stone Ridge, New York, Mimi & Hill cofounder Hillary Kaplan strayed from the grown up, colonial-influenced interiors her design studio is known for. Instead, she blended minimalist architecture with natural materials to create a serene retreat that feels deeply connected to the surrounding Hudson Valley. But more striking than the deviation from Kaplan's signature style is the fact that she did it all in a spec house.Not that she just took the out-of-the-box configuration that came standard. Kaplan worked with developer NevelHaus and INC Architecture & Design to customize the floor plan to better fit her familys lifestyle. She started by reconfiguring the main floor of the five-bedroom, five-bathroom home, flipping the proposed dining and living rooms. This allowed ample wall space for a Samsung Frame TV and a prominent corner spot for a wood-burning stove in the living area, where her family enjoys cozy moments together. Another major upgrade to the 4,400-square-foot house involved increasing the number of recessed lights. Sconces and pendants were also put in for variety. "This layering approach added warmth and character, transforming the space from a typical new build into a more inviting and cozy environment," Kaplan says.In the basement, Kaplan divided what originally was an open layout into a shared bedroom and big family room. The latter doubles as a movie night hangout and pool house. In the home's two lofted areas, Kaplan also did some reimagining. She left part of it open for a reading nook, where her family also avidly plays backgammon. The other part of it was enclosed and functions as an additional bedroom with a pullout daybed that converts into a king-size bed.All of these careful adjustments turned the house into a personalized haven. And better yet, "by not moving any major wall placement from the original spec-house plans, we were able to not have to spend any extra cost on construction," Kaplan adds. Related StoriesLiving RoomNicole CohenTo play up the home's scenic mountain setting, visible through tall windows, Kaplan maintained a muted, earthy color palette. She filled the house with local pottery and midcentury art, which "lends a feeling of established architecture to a newer home." Vintage furnishings made of natural materials and textured accents help ground the space, giving it soul."The home was envisioned as a true mountain retreat, and we leaned into that aesthetic," Kaplan says. "The scale of the main living area was central to achieving this, evoking the open, airy feel of mountain spaces and reflecting the expansive natural surroundings."Sofa: Lee Industries. Chairs: Mazo Design. Coffee table: Lock & Mortice. Rug: Orientalist Home. Wall art: vintage.KitchenNicole Cohen"The beauty of the waterfall edge of the silver wave marble is the true eye catching element in this kitchen," Kaplan says. "It almost appears to be petrified wood merging the organic feel with the function of the kitchen."Wall paint: Cloud Cover, Benjamin Moore. Counter: Peter Brooks Stone Works Inc. Pendants: Allied Maker. Chairs: Lee Industries. Cabinetry: Form.Nicole CohenA small patterned Peter Fasano wallpaper adds elegance to the small pantry tucked behind a glass door. Cerused black oak cabinets hide the large family's everyday needs.NookNicole CohenA nook outfitted with bench seating and a stone top table, both from Four Hands, along with reupholstered chairs from the '70s make the perfect setup for family game nights.Pendant: Arteriors. Dining AreaNicole CohenA vintage cabinet from Hollywood at Home nods to the warm, earthy colors of the Hudson Valley landscape. Light fixture: Bone Simple Design. Table: Four Hands. Chairs: Lee Industries. Candlesticks: Lostine.Primary BedroomNicole CohenRoman Clay walls and handwoven window shades from Hartmann & Forbes make for a truly calm setting.BedVanguard Furniture. Bedding: RH and Parachute. Bedside table: Soho Home. Wall paint: Kerri Walsh Faux Finishing. Table lamp: vintage.Kids' RoomNicole CohenThe row of beds in this guest room are ideal for sleepovers, while the neutral color palette suits the home's serene style. Headboard: Norwegian Wood. Sconces: Lostine. Shades: Hartmann & Forbes. Wardrobes: Four Hands. Wallpaper: Cole & Son. Primary BathroomNicole Cohen"The primary bathroom plays with soft marble tones and light woods to create a spa like environment," Kaplan says.Mirror: Arteriors. Sconces: Allied Maker. Vanity: Vanguard Furniture.Guest BedroomNicole CohenNicole CohenA textured wallpaper by Phillip Jeffries and organic linen bedding make guests never want to leave the cozy, cocooning space.Bed and seating: Lee Industries.Sconce: Hector Finch. Nightstand: Soho Home. Wall art: vintage. Table: Four Hands. Rug: Lulu and Georgia.BathroomNicole CohenNicole CohenThe lower level bathroom is clad in handmade green glazed Fireclay tiles and white oak paneled walls.Wallpaper: Fayce Textiles. Rug: vintage.Follow House Beautiful on Instagram and TikTok.