17 Penllwyn Park

17 Penllwyn Park is a house that originally served as a service wing. It is constructed from rock-faced coursed Pennant stone, featuring yellow brick dressings and some areas of red tile-hanging. The roof is made of slate, with red terracotta ridges and finials. The building has two storeys and a prominent red-brick stack at the north end.

On the left gable, there are bargeboards above a tripartite cambered headed window on each floor, both framed in yellow brick. The upper window is taller and includes small-paned top-lights, while the lower window consists of three narrow sashes with ten panes each. To the right, there is a projecting porch bay with tile-hanging on the first floor, a half-timbered small gable, bargeboards, and a finial. The first floor features a cross-window, and the ground floor has an arched entry with an arched hoodmould. The door is set back from the porch.

To the right of the porch, there is a two-light window on each floor, with small sashes framed in ashlar. The north end has a lean-to with a broad hipped roof and a small gablet at the apex. There is also a four-light casement window located under the eaves on the ground floor to the west.