Plas Llanddyfnan

Plas Llanddyfnan is a gentry house of predominantly Georgian character, built of rubble masonry with roughcast rendered elevations and gritstone dressings, under slate roofs with stone stacks.

The principal block is two storeys with attics and cellars, arranged as a five-window range symmetrically planned with a central 19th-century porch of Penmon limestone. The steeply pitched slate roof features hipped-roofed dormers. Tall rectangular gable stacks with capping sit at each end, the southern stack being rendered. The principal elevation is coursed rubble masonry with large boulders as quoins. The raised central entrance is reached by stone steps with flanking plain railings topped with ball finials. The porch is formed by a single slate slab supported on simple tapering limestone columns on brick piers, with a panelled doorway and radial-bar fanlight above. Ground and first-floor windows are hornless 12-pane sashes; attic dormers have modern casement windows.

The rear comprises three gabled wings. The southern return extends back as a single-window bay, lengthened by an additional single-storey bay with lower hipped roofline and canted in plan. Both are roughcast rendered with matching windows and end stacks; the gabled bay matches the main block, while the extended bay has a rendered shouldered stack with capping. A single modern casement lights the first floor to the rear of the gabled bay.

The central staircase wing has modern windows and adjoins a flat-roofed extension between the flanking bays. The extension's first floor has a fixed 12-pane light; the ground floor contains a tripartite window lighting the stairwell.

The northernmost rear gabled wing meets a three-bay service wing marked by a broad squat stack at the junction and a further ridge stack between the first and second windows. The northern gable return of the main block has a single first-floor 12-pane sash; the original wing has windows to each floor including an unequal sash to the attic gable. Between them, steps descend to the cellar doorway—the only external remains of the original late 16th-century house, featuring a segmental stone head and chamfered jambs with broach stops. The service wing has hornless sashes of 12 and 16 panes, with a doorway set between the second and third windows now topped by a modern timber porch. The southern elevation overlooking the garden has a doorway at the left end under a rectangular fanlight with glazing bars, with matching windows to the main block. At the far left stands a semi-octagonal addition at the southwest corner of the service wing; a linking single-storey bay extends behind it to connect the service wing to the outbuildings range. Both have modern casements in gable dormers; the north elevation contains a doorway to the right and 9-paned fixed lights flanking a large 16-pane hornless sash. Service wing and linking bay are roughcast rendered.

The former outbuildings range, now linked to the house, is of cruder rubble masonry construction, limewashed only on its south garden elevation. It is a single-storey range with hipped slate roof and a single ridge stack to the east end with dripstones and capping. The south elevation features a boarded door offset to the right with a small-paned fixed light beyond, and at the far left an unequal 15-pane sash with a 9-pane fixed light to its right. The north elevation has a boarded door to the west under a blocked window in a gable dormer. To its left, the range links to the stable range via an archway under a gabled roof, with a further doorway to the outbuildings range beneath the linking arch.

The principal range dates to the early 18th century and retains a dog leg staircase with clasping rail on stick balusters and dado panelling. Some panelled doors remain along with simple cove moulding. The service wing has been internally modernised. The only documented remains of the earlier house are the cellar beams and doorway.