For interior designer Charlotte Moss, one of the perks of townhouse living is the ability to host parties for good causes – the New York City Ballet, Unicef, and the Parrish Art Museum, to name a few.

Last week, Ms. Moss’s home, decorated in her signature classical and airy style, seemed perfectly matched to the cause. The cocktail party was toasting the first recipient of the Fashion Institute of Technology’s Couture Council award, designer Ralph Rucci, also known for his classic, timeless designs. The Ralph Rucci suit Ms. Moss wore to the party was the perfect complement to the home’s decor.

“It’s all about giving what you can when you can. I love being at home, so I’m happy to share it,” Ms. Moss said.

Ms. Moss had prepared for company. Candles were lit and full bouquets of peonies covered various tabletops throughout the six-story home built in the 1920s. Ms. Moss and her husband, investment banker Barry Friedberg, have lived there since 2003.

But one by one on this beautiful spring night, guests such as Martha Stewart, Amy Fine Collins, Patsy Tarr, and about 50 others, bypassed the staircase and headed straight to the 100-square-foot garden.

Ms. Moss understood. “It’s probably my favorite room in the house,” she said of the gracious 100-square-foot space whose focal point is a circa-1810 French limestone fireplace, converted to gas. “I love alfresco dining,” Ms. Moss said. “And because you can see the fireplace from the front door, it draws you in and you don’t want to leave.”

So the interior rooms, models of balance and proportion, remained empty. What guests could see from the garden were the striking sets of floor-to-ceiling windows on the second floor. In the living room, they are actually French doors opening onto petite balconies overlooking the garden, framed by curtains in Christopher Norman green and white stripe. What guests did not see were the floral motifs in the carpet and fabrics and the light-pink and green upholstery. They are subtle, ceding the visual punch in the room to the three large paintings of the gardens of Versailles, by Paul Cesar Helleu, and a bust by Louis-Pierre Deseline.

Across the hall the library has a more cloistered and masculine feel, with the same triple set of windows extravagantly draped in bronze Fortuny fabric. The room has high ceilings, but remains cozy because of the intimate scale, set by the shelves of books, an early 19th-century music stand, and a gold clock with a sunflower face at the center of the mantel, which Ms. Moss spotted in a window in Paris.

Ms. Moss has looked after every detail, even in the hallways. On the fifth floor, the antique piece that first greets the visitor is an 18th-century jardiniere table filled with succulents. On the street side are an exercise room and guest bedroom. On the side facing the garden, Ms. Moss’s office showcases the light blue fabric “patterned after a decorative painting technique.” The pattern doesn’t distract from her wall of muses, featuring classic photographs and sketches of women such as Coco Chanel and Grace Kelly. Ms. Moss’s passion for style also shows in the shelves of Harper’s Bazaar and Vogue magazines from the 1940s, elegantly bound in red leather. This is the room Mr. Rucci and the director of the Museum at FIT, Valerie Steele, who is preparing an exhibition on the designer, may have liked best, had they made it past the garden.

It’s likely they’ll have another chance, though, because Ms. Moss loves to throw a party, and does so for charities she cares about “whenever the need arises.”

“It’s my Southern hospitality gene,” the Richmond, Va., native said. How fortunate she has brought her charm to Manhattan.