In the medieval period Vaynol was owned by the Bishopric of Bangor, and was made over to the Cochwillan family in 1533. It eventually came into the hands of the Williams family, William Williams being High Sheriff of Caernarfonshire in 1598, and created a baronet in 1608. It was held by this family until 1696, and by 1723 it was in the hands of John Smith MP, who built the new hall.

An inventory of 1660-1690 records a total of 44 rooms, and the building appears to be of three or four phases. It originated in the earlier sixteenth century as a two-unit house with a lateral chimney, on the ground floor it comprised of a hall, passage and small outer room. In the mid-seventeenth century it developed into a E-plan house, with the addition of a storeyed porch over the entrance and a similar oriel bay at the east end. To the rear is a stair wing dated by its close-studding to 1638. Towards the end of the seventeenth century there was the addition of a much larger wing on the west side. In the nineteenth century a number of outbuildings were attached to the west wing.

The hall is built of local rubble, with large quoins, freestone dressings and slate roofs. The main east-west range is two-storeyed, with a perhaps contemporary three-storey wing on the east, which would have held service rooms on the ground floor. The added porch on the north side has an open, outer, moulded Tudor arch with a sqaure frame, the spandrels decorated with shields. The windows are generally of 2-, 3- or 4- lights, and are stone mullioned with round heads to each light, set back in chamfered ashlar surrounds. one of the 3-light windows in the porch gable, and the gabled oriel wing has 3-over 4- lightarched Tudor windows.

The east wing has a door to the undercroft of the main range with 5-over4-light windows and similar windows to the rear wing. At the west end is a balancing wing with crow stepped coping, a 4-light window to the ground floor and a stone mullion cross window above.

The inner arched doorway from the porch has a cahmfered oak frame and boarded door, with flowers and foliage in the spandrels. This directly accesses the main hall which has bar-stopped chamfered ceiling forming a coffered ceiling The room is fully panelled with 17th century, moulded, square panelling which was removed to New Hall but has been returned. The cross passage leads to the rear wing, with a fine 17th century boxed stair. This has square oak newels with inverted urn finials and pendants, and turned, waisted balusters. The stair well is timber framed with wattle and daub, and lath and daub infill.

The great 3-bay chamber over the hall has a stone fireplace with a jogged lintel and an oriel window with two lights. A timer-framed partition has a central pointed arch doorway. The surviving trusses have collars and raking struts and two tiers of purlins. The initials 'TE 1831' appear on the plaster. In the cellars the rear chamber formed the late 17th century kitchen, with a huge fireplace on the south end wall. A stone, chamfered doorway, originally external, leads to the angel below the later kitchen and the stair.

(Based on CADW listing description)

S Fielding, RCAHMW, 23 May 2005