Y Garreg Filltir with rear low wall and railing

Y Garreg Filltir is a house built with painted stucco and features a slate hipped roof, bracketed flat eaves, and tall stucco end stacks. It is two stories high and has a three-bay southeast front, which includes hornless 12-pane sash windows above two French windows that have marginal glazing bars and a central arched niche. The left southwest end wall has two 15-pane hornless sash windows closely set in the center of the first floor, and a large arched window (which was converted into a door in 1981) on the ground floor right, featuring a radiating-bar fanlight above a fixed window that was likely a former door, all with marginal glazing bars.

To the left, there is a 20th-century lean-to conservatory with an arched window, a former door with a traceried fanlight, reeded pilasters on each side, and a moulded arch. A 20th-century window is also present. The right northeast end of the house has an arched window in the center of the ground floor with 20th-century glazing, a 20-pane sash window each floor to the center right, and a 10-pane sash window each floor to the right.

At the rear, there is a 12-pane sash window to the right and a northeast rear wing set back to the left with 20th-century glazing and alterations. This wing features an 8-pane window in the angle above a door, and on the first floor, there is a 12-pane sash window above two 16-pane windows. There are also two 20th-century ground floor arched openings to the left. The northwest gable end is two stories with an attic, featuring two 9-pane attic windows, two 12-pane first floor windows, and a large porch, all from the 20th century.

The northeast side of the wing has a three-window range that is continuous with the right end of the main house, with close eaves, sash windows, and a door to the left in a 20th-century glazed porch, along with a raised truncated side-wall chimney breast to the right.

A short quarter-circle low wall and railings are located by the northwest end of the house; the wall is made of painted brick with stone coping, and the iron railings feature fluted columns on a vase form with finials, similar to those in front of Furnace House on St Peter's Street. The house has undergone significant alterations during renovation, including arches in the end walls of the southwest rooms, with one arch in the southwest room now converted into a window.