In 1926, Sleeper purchased a brick double house at 90-90A Chestnut St., gutted the interior, refaced the exterior with dark Gloucester brick, added a fourth floor with a limestone balustrade and installed an elevator.

On the Flat of Beacon Hill is a four-story townhouse that was once home to one of the country’s first interior designers and, remarkably, many of his inspired details and embellishments have survived for more than 90 years.

Henry Davis Sleeper is best noted for his magnificent mansion on Gloucester Harbor, which he designed initially as a three-room cottage in 1907 and expanded it during the decades to become the architectural showplace it is today.

Called Beauport, it is now owned by Historic New England and is on the National Register of Historic Places.

In 1926, Sleeper purchased a brick double house at 90-90A Chestnut St., gutted the interior, refaced the exterior with dark Gloucester brick, added a fourth floor with a limestone balustrade and installed an elevator.

For his in-town Boston home, he occupied only the first floor and garden level and leased the three upper stories. Yet the interior is elaborate, much smaller but similar to Beauport, with rich paneling, crown molding with gilt accents along high ceilings and fireplaces with various marble mantelpieces.

During the past six years, the present owners combined the living spaces into a grand 6,500-square-foot single-family residence, perfect for entertaining, restoring architectural details throughout and updating other features.

Tracy Campion of Campion and Company Real Estate has listed this five-bedroom home for $6,500,000.

The exterior has four doorways – the main entrances to 90 and 90A Chestnut, each featuring bull’s eye windows and fanlights. In between are two smaller doors; one is what was the servants’ entrance; the other conceals the elevator. A huge window is in the middle.

Especially unique to this home is the sidewalk in front of the doorways, which comprises three panels of glass blocks that Sleeper designed to draw in natural light for the breakfast room and kitchen on the garden level below.

Last year the owners totally renovated the area, replacing the old glass blocks and adding structural steel and reinforced concrete, thus ensuring its strength while maintaining Sleeper’s design.

The building is trimmed with limestone sills and lintels, and above the middle second story window the lintel is recessed and holds a Romanesque statue of a reclining woman.

Inside at 90 Chestnut, a beautiful mahogany-paneled reception room lies to the right of the entry and boasts a wide bowfront leaded glass cabinet in between a closet and a large window seat. Access to the elevator is just inside the front door.

A carpeted staircase ascends to the spacious main living space with a parquet floor. Three windows face Chestnut Street and in between them are paneled doors that hide the elevator and a wet bar with a refrigerator and brass sink.

Matching glass cabinets above the stairwell and against the living room wall face each other in symmetrical fashion, and the ceiling boasts an oval oculus equipped with LED lighting. Originally, natural light filtered down from a roof skylight.

At the far end of the room is a corner fireplace. In the other corner are stairs to the upper floor. And in the middle is the opening to an L-shaped study, which includes built-in shelving and a charming marble fireplace. Its surround has a carved wolf and crane from Aesop Fables. This room also has a powder room opposite a three-bay oriel.

The next level comprises a large family room with a wide Adamesque mantelpiece and two oculi, the main kitchen and a bedroom suite with a three-window bay. An en suite bath with a combination tub/shower and a stone-topped vanity is next to a wine closet.

At the front of the house are a butler’s pantry with a zinc-lined sink and a tiled floor and a large kitchen with a beamed ceiling and skylight, antiqued pickled pine cabinets, a stainless steel Samsung refrigerator, Miele dishwasher and six-burner gas range. A laundry closet holds a stacked washer/dryer.

Nearby is a second staircase - skylit - that ascends to the master bedroom level and to the roof deck.

The top floor is an outstanding retreat. A Juliet balcony is off the master bedroom, next to another fireplace, and a big skylight with electronic shades bathes the room with light. On an opposite wall, the former owners added a wall of closets and drawers for clothing.

The en suite mirrored master bath has a huge, square water-jetted soaking tub beneath a skylight and a double vanity. A pocket door encloses the commode room, adjacent to a closet.

A second bedroom suite lies beyond the master and includes a fireplace and a full bath. Presently it serves as a home gym.

The 800-square-foot roof deck has recently installed gas, water and electric service for entertaining and comfort, and the views are panoramic.

More living space is available in Sleeper’s original quarters. What was his living room is now used as a spectacular dining room, accessed from the mahogany-paneled reception room or from an octagonal foyer connected to the entry from 90A Chestnut.

At the far end of this space is a room with an en suite bath, which was Sleeper’s bedroom, according to the owners. It looks out to a garden and the back of a brick building on River Street. To please his eye, Sleeper commissioned a faux door with a pediment beneath a faux window.

Next to the octagonal foyer is an angled staircase that mimics one at Beauport and descends to the garden level. At the tiled base of the stairs is a wall of original cabinetry with interior lighting. This stair hall connects to a large Victorian-style oval-shaped room with a fireplace with an elaborately carved mantelpiece. Beyond it are a heated winter garden room with a glass-block ceiling and a guest bedroom with a walk-in closet with a window. A full bath is close by.

At the front of the house is a large kitchen with the breakfast room beneath the glass-block sidewalk. The kitchen has a gas range and a china cupboard accessible from three sides and the breakfast room beneath the glass-block sidewalk. A laundry closet with a stacked washer/dryer and a handy workshop are on this level too.

Around the corner is the Brimmer Street Garage, where a deeded parking space will be conveyed with the sale of the home.