Dyffryn House is built in an eclectic design derived from the French Renaissance and English Baroque styles, the former is particularly seen in the Mansard roof and some of the window treatment and the latter in the Great Hall block to the main facade. The building is 2 storeys and attic and has a hipped mansard slate roof with balustraded parapet over the main cornice. The main front is dominated by the tall, square Hall block that projects to left of centre; this has balustraded parapet with urns and a pedimented front over a giant, round-arched window. The symmetrical part of the design is that there are 3 storey 'towers' to the centre and ends. The ground floor is advanced to right of the hall block with similar parapet and urns. In front of the hall block is a projecting lobby/porch and a porte-cochere onto the Carriage Court; this has paired Doric columns and a rusticated entrance surround. There is a symmetrical 13-bay garden front to the south including projecting end 'towers' and broader projecting central bay, which is pedimented in a similar manner to that of the hall block. The 'towers' have niches containing statues to ground floor. Midway between the central and end bays are 2-storey splayed bays; these are linked to the central classical veranda which has paired Doric columns and balustraded parapet with ball finials. A modern extension to the west and beyond that is the converted former stable courtyard with pyramidal clock-tower to south range, originally the coach-house.

Reference: Cadw listed buildings database.