Llanerchaeron, including rear Service Courtyard Ranges (previously listed as Llanaeron House)

Llanerchaeron is a two-storey house of roughly square plan with a lower service wing to the north and a single-storey service court beyond. The main block and service buildings are constructed in rubble with colourwashed roughcast elevations over red brick. Slate hipped roofs are valleyed to the north of the main block and service wing, with broad bracketed eaves. The chimney stacks are of red brick, largely renewed around 1900, with three stacks to the inner slopes of the main part, two thick stacks to the north wall, two to the inner slopes of the wing, and four to the courtyard ranges.

The entrance front to the east comprises three bays with a recessed centre bay. A large projecting Greek Doric porch was added after 1845, featuring paired fluted columns, an entablature and balustrade. The inner door is a four-panel example with side lights and a large traceried fanlight. The first floor has 12-pane hornless sash windows; the window to the right is set lower, a modification made in 1920 that reflects the lower level of the earlier house, which the architect John Nash had ignored in his original fenestration. The ground floor left window contains a Venetian window set within a round-arched recess, with tripartite sashes of 4:12:4 configuration and pilaster jambs to the narrow side lights; the arch is in stucco with fluted enrichment. Though glazed, this window is blind. The right-hand ground floor has a canted bay window of 1854 with 12-pane sashes.

The south front is of five bays with 12-pane hornless sashes and painted stone sills. Ground floor windows are set in round-arched recesses. The west front comprises three bays, with similar sashes to the first floor, the left window set lower for the same reason as the east elevation. The ground floor features Venetian windows; the left one has been altered and lacks an over-arch, though the glazing pattern matches the east front. The other two have early 20th-century plate glass.

The service range is plain in design, constructed in rubble with a modillion eaves cornice. It is double in depth with a five-window range of 12-pane sashes to the west, with brick surrounds. On the ground floor, the second window from the right has been relocated, and at the centre is a canted 4:12:4 timber bay window. The east side has paired windows under broad cambered brick heads, with two pairs of 6-pane sashes to each storey. The right pair is partially obscured by a single-storey gabled kitchen addition.

The rear of the service range forms the north side of a picturesque enclosed service court with single-storey ranges on three sides. The rear elevation of the service block has wide cambered windows to each side on both storeys and a pair of six-panel doors with four-pane overlights at the centre. The upper windows are low with paired 6-pane sashes. Most lower windows are boarded over. Slate sills are throughout. A pent roof covers the ground floor, currently undergoing restoration; paired putlogs above the doors suggest a large porch may once have been intended. The service ranges have blocked doors to each return wall adjoining the service block.

The single-storey ranges have deep overhanging slate or corrugated roofs, with supports on the east side probably of secondary date. The eaves to the west range have been cut back. Construction is of colourwashed render over rubble. The west and east sides are matching, each featuring a large elliptically headed recess at the centre containing a tripartite window and two round-arched doorways either side with tripartite fanlights. The second door from the left on the east has been altered. Red brick surrounds frame the openings throughout. The north range is slightly later in date and contains a central entry passage. The courtyard elevation has a central round-arched entry with stone voussoirs. Arched doorways flank this entry, each with six-panel doors and fanlights with stone voussoirs. Outer doors to either side have brick surrounds; the left has a six-panel door and the right is blocked. The north (outer) elevation features a cast iron fanlight to the entrance and a boarded door. Two wide windows flank the entrance on each side; the outer ones have 2-light 16-pane glazing, with stone voussoirs throughout. The outer elevation of the east range has a wide elliptically headed 12:24:12 sash at the centre with slate sill and brick surround, replacing two earlier brick-arched openings. Two 9-pane windows to the right have slate sills and brick dressings to the left and timber lintel to the right. Small hipped water closets occupy both outer angles with the rear wing, each fitted with a 12-pane horizontal sliding window.

The older house occupies the site of the rooms on the north side of the main block, which are on a lower level and have stone-vaulted cellars, creating an interesting ground floor plan. The entrance hall, with a modillion cornice, opens into a square domed inner hall with arches on four sides. The west arch leads to the Drawing Room, which has a shallow elliptical south end, an early 19th-century neo-Grec fireplace, plaster cornice and panelled window shutters. To the south is the Dining Room with a modillion cornice and Victorian fireplace. Both rooms have six-panel doors with outer raised beading. An arch to the north gives access to a top-lit stair hall containing a double return cantilevered stone staircase with scrolled wrought iron balustrade and wooden handrail. The timber top-light was added in the early 20th century, when the roof was slightly reordered. The older part of the house has oak floors, whilst the remainder are of deal. The doors in the older section feature six raised and fielded panels, which may be of mid to late 18th-century date. The Library has a simple plaster cornice, as does the Morning Room, which contains a late 19th-century fireplace.

The first floor features a domical vestibule with a glazed cone, probably not original, over a moulded plaster circular opening fluted on the inner face with guilloche work to the underside. The plain southwest and southeast rooms are accompanied by a Dressing Room between them with plaster cornice and coved ceiling, the upper part framed by reed moulding, and a simple marble chimneypiece probably of 1794. The northeast and northwest rooms are also plain. Of principal importance are two oval dressing rooms. The east one has curved corner niches and a large ceiling centrepiece of radiating feathers with a wreathed cable-type cornice. The west dressing room has a cornice, plaster ceiling roundel, curved corner niches and a simple late 18th-century chimneypiece. Both rooms are fitted with curved six-panel doors.

The first floor of the service block contains a suite of three rooms to the west; the southern room has a concave chimney-breast and a plain Nash fire surround, with round-arched eight-panel doors to each side. An early 20th-century back stair replaces an earlier spiral staircase, dating from when attic rooms were lost due to roof alterations.

The ground floor of the range is served by a spinal corridor, with two large kitchens to the east featuring substantial fireplaces, the larger with an elliptically arched opening. Housekeepers' rooms to the west contain fitted cupboards. The service ranges include a large room to the west with a segmentally arched plaster ceiling, currently derelict, and slate salting troughs. The northeast room has a brick oven. A brewhouse occupies the northwest corner.

The building was undergoing restoration by the National Trust at the time of listing documentation (summer 1995).