Second-floor lounges are trending as a family gathering space. They’re cozier than the living room downstairs and offer more privacy.

One couple calls their second-floor living room the “healing chambers.” Another homeowner calls it the “feasting room.” Others refer to “pajama lounges.”

Regardless of the name, developers, architects and real-estate agents are increasingly getting requests for upper-level living rooms. The spaces are typically located right off the bedrooms and equipped with comfy sofas, kitchenettes and high-tech toys. Homeowners say second-floor lounges are cozier than open-plan living areas downstairs and offer more privacy because they’re above street level.

Kobi Karp, a Miami-based architect, earlier this year created his first spec home with upper-level indoor and outdoor living areas, which was listed for $25 million. The lounge was intended for “the bedrooms [to] spill out and the family can have a space to assemble,” he says. “It’s where you go on a Sunday morning and wait for the rest of the house to wake up.”

Mr. Karp says he encourages children and parents to hang out in the space while focusing on different things. The areas are equipped with a television and multiple nooks where family members can work in proximity without interrupting one another. “We’re seeing more sharing of spaces,” he adds.

Requests for upper-floor living spaces called pajama lounges started trickling in at the request of South American and European clientele who were used to similar rooms back home about 10 years ago, says Miami-based architect Ralph Choeff. More than 50% of the homes designed by his firm, Choeff Levy Fischman, now offer the feature. The rooms have built-in shelving to hide electronic cords and clutter, along with mini-kitchens and comfortable spaces for lounging. To make room for a central living area upstairs, Mr. Choeff eliminates most hallway space and minimizes seating areas in individual bedrooms.

In her previous home, Dianne Burnett says she walked down a hallway “like a hotel corridor.” Last year, Ms. Burnett, an author and producer, paid $3.3 million for a 4,000-square-foot home in Malibu, Calif., with a second-floor living area off the bedrooms. The room is designed entirely for lounging, with a TV, cushy seating and a skylight.

One unexpected perk is that Ms. Burnett uses the communal living area as a way to keep her electronics usage in check without the need to traipse downstairs every time she wants to open her laptop or turn on the TV. “I’m trying to be the type of person that doesn’t have the television in their bedroom anymore,” she says.

Upper-level rooms can be a tricky space to decorate. Many have awkward layouts and uneven ceiling heights because “they are usually more of an afterthought for the builder,” says Donna Mondi, a Chicago-based interior designer. Unlike the kitchen and living areas on the first floor, Ms. Mondi creates a space that’s more casual using indoor-outdoor fabrics, recessed lighting in lieu of chandeliers and cozier seating areas rather than larger sectionals. There’s no need to match the style to the rest of the home. “Because it’s not part of the main area, all bets are off—you can do what you want with it,” says Ms. Mondi.

Two years ago, the designer helped homeowner Sam Tornatore create a “feasting room” in the second-level living area of his Oak Brook, Ill., home. The space has two seating areas, a fireplace and a formal dining table that he uses for holiday gatherings. Positioned near the roof of his 8,000-square foot, eight-bedroom, five-bathroom French Country-style home, the wood beams and iron light fixtures give it a more “Crusader 15th century, Charlemagne feel to it,” says Mr. Tornatore, a 63-year-old entrepreneur in financial services. He purchased the home in 2012 for $1.85 million. Another $95,000 went toward finishing the space, says Ms. Mondi, the designer.

The concept of an out-of-sight upper floor gathering space isn’t new. Piano nobiles, or noble floors, were built inside Italian palazzos, where receptions were often held on the second floor for safety and sanitary reasons, says T. Jeffrey Clarke, a Philadelphia-based architect specializing in historic preservation. Other historic homes would also have an upstairs “retiring room” for mothers nursing children or resting midday, he says. When he designs homes, he makes sure that the upper-floor living room is small enough to feel proportional to the low ceiling height found in some historic homes, he adds.

When developer Francis Greenburger converted part of a former school in New York’s Nolita neighborhood into an 8,069-square-foot townhouse, he decided that he wanted more “discrete living spaces” throughout. In addition to the main kitchen and living space, Mr. Greenburger, the 68-year-old chief executive at Time Equities, worked with architects to create an upper-floor living area located between two of the townhome’s seven bedrooms and has round oculus windows and exposed wood beams. “I used my own life experience, and imagined if I lived there with my four kids,” says Mr. Greenburger about the home, which is listed for $25 million.

In Malibu, Calif., real-estate agent and reality-TV personality Madison Hildenbrand says he has sold a dozen homes with the amenity in the past three years. “After living in [an open-floor] situation, they realized that it’s nice to have the big open spaces, but also a little bit annoying,” he says. “Now there’s a bit more compartmentalizing.”

Upstairs living areas that cater to the entire family are helping larger homes that already have multiple bedrooms sell faster these days, says Mr. Hildenbrand. The feature is popular among families that want extra space to hang out without making an office or playroom serve double duty.

Inely Cesna and Mike Murphy call the upstairs living area of their Spanish-style 11,525-square-foot, five-bedroom home in Malibu the “healing chambers.” It has a fireplace and terrace with water views. When their children were younger, they used the space to eat breakfast or recover from a cold. “It was really the room where we would spend time together,” says Ms. Cesna, 50, an attorney who works as a mediation coach.

Recently the couple listed their home for $7.75 million with Mr. Hildenbrand’s firm. Why? Their children are older—11 and 14—and now want to retreat to their bedrooms for privacy, Ms. Cesna says. Currently they’re renting a smaller home with open spaces so they can keep an eye on the kids or overhear their conversations. “Even when they say ‘don’t bother me’—we want to be in close physical proximity,” she says.