There is fifteenth century poetic reference to a house called 'Plas Peniarth' occupying the site of the present house. The earlier house was enlarged by Richard Owen around 1700, as indicated by a stone cartouche. His son, Lewis Owen, carrried out some improvements to the house and probably laid out the surrounding park. A daughter, Jane, married Richard, 5th Viscount Bulkeley of Cashel, MP, in 1731 and his arms appear in the pediment on the front of the house. He probably applied the fashionable Palladian style brick front around 1729 to 1739. Peniarth then passed through the offspring of Jane's second marriage to the Wynne's of Wern, Portmadoc. The later William Watkin Edward Wynne MP (1801-80) became a distinguished antiquary and collector, inheriting and adding to the Peniarth Manuscripts, the most important collection of Welsh manuscripts, now in the NLW. From 1834 repairs and improvements were carried out, including the addition of the portico to the front in 1858.

The building is approximately square in plan, and of 3 storeys, attics and cellar. The earlier part of seventeenth century or earlier date occupies the north-east side, and is built of slate stone, faced with brick, made on the estate. The enlargement to the rear of around 1700 is constructed in a larger gauge rubble stone, with stone lintels to openings, the whole then covered with a hipped slate roof with a central valley. The ground floor was, in 1858, enclosed within a single storey brick portico extending to the full width. There are stone pilasters supporting a continuous Tuscan entablature. The doorcase is of stone, with a moulded eared architrave rising to a pulvinated frieze and cornice, the arms of Wynne are suspended at an angle above.

Source: Cadw listed buildings database.
Source: Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 632.

RCAHMW, October 2009.