Vaynol Estate was given to the the crown after the last of the Williams family died without issue in 1696. Before 1723 the estate was granted to John Smith MP, Chancellor of the Exchequer and Speaker of the House of Commons. In 1764 it was let to Thomas Assheton of Cheshire, who took the name Smith; marriages of various descendants introduced the names Duff and Vivian into the name. The estate was enlarged enormously from the wealth created by the Dinorwic Slate Quarries, although much of the property was sold by Sir Micheal Duff in 1967, the rest of the estate sold after his death in 1980.

Vaynol Hall replaced the Old Hall as the main residence of Vaynol Park. It was built in the mid 18th century, and extensively remodelled in the 19th century to create the present mansion. Alterations in the early and mid 20th century, later converted into flats.

The building is three storeys on an L-plan, and has white stucco walls with a slate roof behind high parapets which have a band and slight cornice. The south-east front is of 10 bays, with a canted three-storey bay and a right hand wing also advanced and canted. The ground floor windows are in shallow recesses and are16-paned, horned sashes. The canted bay holds a panelled door with an overlight. Set back at the south-west end is a two-storey stair projection with a tall window.
The north-east front has the main entrance from the driveway in the re-entrant angle. A classical portico was added in 1910 with awinged symbol on the fascia. Behind this is a lobby with a domed roof.
The south-west front is of seven bays which includes a splayed ground floor on the right. The garden on this side is bordered on the south-east side by a rebuilt brick wall with acorn finials and closed to the south-west by a balustrade with a concrete handrail, terracotta balusters and oval fluted urns.

It has a mid Georgian interior with complex plan. the principal rooms are in the eastern part leading of a rectangular innner hall. Many rooms have elaborate plasterwork, and there are panelled doors throughout. Many areas especially corridors have panelling, and there are many fine marble fireplaces. Grand staircase is in a panelled hall and has a cantilevered upper flight. It has barley-twist balusters, foliate tread ends and a marbled handrail, and the stairwell is lined with striking plasterwork in vertical, naturalistic trails. One of the public rooms has a Roccoco ceiling, while the main drawing room is fitted in the Palladian manner, the quality of work being very high and reflecting the most up to date fashions. There is an added circular lobby in the grecian style decorated with trompe l'oeil paintings depicting local scenes including Dinorwic Quarry and Vaynol.

A gasometer was marked on the 1913 to 1949 OS maps, indicating a private gasworks to the estate.

(Based on CADW listing description) S Fielding RCAHMW 17/05/2005