Plas Dinam is a well preserved and nationally significant example of the Domestic Revival, or 'Old English' style fashionable in the mid-late Victorian period, exhibiting a skilful use of traditional materials to create a successful composition. The mansion was designed and built in 1873-4 on a site previously known as Penybryn, by architect, William Eden Nesfield (1835-1888).

The house is organised around the large medievalising hall on the north side, with withdrawing rooms to the west, domestic arrangements to the east, and various ancilliary accommodation in linking west wing. It is built of red brick and local greywacke rubble, tightly jointed, with limestone dressings, a timber framed storied porch with infill panels, and has silvery-grey small slate hanging. The Gothic pointed door is set behind the recessed limestone ashlar porch. Inscriptions carved each side read: PAX INTRANTIBUS and SALUS EXEUNTIBUS. Flanking columns support shaped timber brackets for the deeply jettied first floor, with moulded and brattished bressumer. There are large stone mullioned and transomed windows and a deeply projecting gable with carved bargeboards. A tall ribbed brick chimney is attached to the west wall. The leadwork has the sunflowers and pies characteristic of the Domestic Revival movement. The kitchen and service rooms are independently gabled, with similar stone dressed windows to the ground floor, the kitchen single storey with a lead and timber roof ventilator and pyramidal spirelet.

Internal features include a moulded plaster ribs ceiling in the medievalising hall, 17th century wall panelling in the dining room (probably taken from probably from Llandinam Hall), a lateral fireplace bearing the date, the Crewe arms and monogram initials, a moulded fire beam obtained from the timber framed house, Pertheirin, in Caersws and a small library in the SW corner with original fittings.

After Lord Davies of Broneirion acquired the house for his residence, it was altered and extended to the east in c.1897-8, including the construction of a Billiard Room wing, and later to the west by E. S. Hall c.1926, using a hard red mechanical brick. These latter extensions have now been removed and the house returned more nearly to its original form.

Associated with:
Park/gardens (Nprn265609).

Reference: Cadw listed buildings database, 2010.