Ystrad Isa

This is a medium-sized F-plan house, dating from the early 19th century, with a two-and-a-half storey L-shaped main block, a rear wing, and a lower service wing recessed to the northeast. The primary structure is built of red/brown brick, with the service wing featuring a limestone rubble plinth. It has slate roofs with a stone ridge to the main block, and slab-coped gable parapets. Simple, flush end and lateral chimneys are present.

The symmetrical front facade features three bays, with a two-storey porch projecting centrally. The porch has chamfered corners to the lower stages and a gabled upper section that is curiously squinched out with large corbels of shaped limestone. A flat-arched entrance is framed by fine brick voussoirs, with a panelled Regency wooden doorcase and a contemporary six-panel door. A cross window is located to the left return. Segmental-arched windows have wooden ovolo-moulded mullions and transoms with leaded glazing, and feature projecting tiled sills. Two-light attic floor windows are contained within flat-roofed early 20th century dormers.

The rear (southeast) elevation is C-shaped, facing the garden. It has projecting outer wings to the left and right, with the right wing being slightly longer. The first floor of each wing has three-light mullioned and transomed windows, while the ground floor has five-light mullioned windows. A recessed central section has a four-light transmullioned window to the first floor and a five-light mullioned window to the ground floor. All rear windows have early 20th-century chamfered sills and lintels of brown sandstone, and decorative iron window furniture.

A two-bay brick service wing is located to the northeast, with windows matching those of the rear elevation and a boarded door providing access to a rear entrance.

Internally, the former hall features stopped-chamfered spine beams with run-out stops, and plain joists. A wide, depressed-arched brick fireplace includes small round-arched flanking niches, each with a six-panel fielded oak door. A fine, full-height dogleg staircase has turned columnar balusters, paired broad baluster newels, a moulded rail with flat capping, and scrolled tread ends. The staircase ascends to the attic, terminating in a short gallery. Galleries are also present on the first and second-floor landings, designed in a similar style to the staircase. The principal ground-floor rooms each have lugged and moulded doorcases framing six-panel fielded doors. The drawing room has two such entrances, suggesting it was originally two rooms combined during an early 20th-century restoration. The room is characterised by moulded plaster cornices and an early 20th-century Adamesque wooden fireplace.