Serving as his own architect, John Penn selected architectural elements for The Solitude that resembled those in English buildings designed by Robert Adam. From his own amateur plan of the interior space, Penn’s layout was only slightly improved in execution by his carpenters.
As one of the first neo-classical houses in America, The Solitude set an architectural trend that others followed. The house, its oval courtyard and detached kitchen—connected to the house by an underground tunnel—occupied a 15-acre knoll overlooking a stream flowing into the Schuylkill River below the house. The tunnel, which led from the basement of the house to the detached kitchen (or kitchen dependency), is still in existence today and is the only apparent example of an underground passage built for the dedicated use of servants.
The Solitude by itself is only 29 feet wide by 29 feet deep with two-and-one-half stories that Penn carefully worked out to be 12, 10 and 7 feet high. Its buff-colored exterior walls are rough stone plastered with stucco and scored to simulate rectangular blocks of limestone, setting off white wood trim. A portico entrance door is its only external ornament. There were no exterior shutters.
Each floor of The Solitude is designed around a single room—the parlor on the ground floor
and the library on the second floor—these are the most elegant rooms in the house. The exquisite
plaster ceilings in the entrance hall, parlor and library remain the best example of the Adam style in Philadelphia. French doors in the parlor open eastward onto a pillared portico, and Penn’s Sheraton-style bookcases still line the library walls.
The room arrangement of The Solitude was built with invisible barriers separating public and
private spaces. On the second and third levels, a combination of squares and other more complex
spaces were arranged without axial symmetry. For example, on the second floor, the library is a near square within the larger square that forms the overall dimensions of this level. However, the
library and a smaller square bedroom are juxtaposed with a semi-octagonal bedroom and stair landing with a diagonal wall. The rooms on this level can be accessed through connecting doors. From the stair landing, however, the diagonal wall hides the library door providing servants with
passages to move throughout the house and to the third level stairwell without disturbing Penn in his
library. Alternately, when Penn occupied the semi-octagonal bedroom, the servants could move
around him by passing through the library. Spatial movement on the second level is essentially diagonal, between the two stairwells placed at opposite corners of the floor. The path chosen by servants or visitors was governed by the position of Penn.