A large double pile Jacobean mansion built within the medieval castle (NPRN 25593).
The house was begun in about 1660. From 1702 until the mid nineteenth century it was divided up. A major restoration, from about 1910, was followed by major fires in 1934. Further renovation occurred in the late twentieth century. The house remains half ruined.
The house was approach by a carriage drive from the south and shows its main front to the town on the north-west. This facade is three storeys high and seven bays long. Each bay is topped by a Jacobean curvilinear gable and finial. There are massive brick chimney stacks. A tall first floor window rises over the blocked central doorway. It seems likely that there was a terraced garden between the house and Castle Street. On the north-east the house abutts a surviving castle tower, a massive, butressed, structure that flanks both entrance and terraced garden.
The house walls are of coursed rubble with freestone dressings.
A service range, with stables and coachhhouse appended (NPRN 31181), adjoins on the south-west. A further service range (NPRN 31182) runs parallel to this on the north.
Associated with: grounds and gardens (NPRN 86069)
Source: CADW Listed Buildings Database (7405)
John Wiles 13.03.07
 Tree-ring dating commissioned by RCAHMW reported in Vernacular Architecture, vol 39 (2008), pp. 141-2:
1. HAY-ON-WYE, Hay Castle (SO 299 423)
(a) Castle House roof Felling date range: 1616–46
(b) Castle Keep, fireplace lintel Felling date range: 1576–96
(c) West Gate, north leaf (replacement) Felling date range: 1610-40
(a) Ex situ timbers 1497, 1587, 1610(5); Site Masters 1321-1497 hay8 (t = 9.3 LYDBURY; 8.2 WALES97; 7.7 SALOP95); 1405-1587 hay5 (t = 5.6 BRECON1; 5.4 CRADLEY; 5.2 TYNCELYN); 1467-1610 hay1 (t = 6.8 ELSTEAD; 6.1 BOWDLER2; 5.9 DITTON4). (b) Fireplace lintel 1536 (h/s + 40-60C NM); Site Master 1473-1536 hayL (t = 7.3 CALLGHTN; 7.0 BUILDWAS2; 6.6 RHOSFAWR); c) Planks 1517, 1550, 15702, 1583, 1591, 1593, 1599(h/s), 1599(1), 1603(4); Site Master 1445-1603 HAYGATE1 (t = 8.8 VOWCHURCH; 8.7 CHAWTON6; 8.7 WALES97).
Hay Castle is one of numerous castles in the March, but is unusual in that it has been continuously occupied for the last 800 years. It has a residential keep of c.1200 with a C13/C14th gateway with pointed archway and portcullis slot. The gate has two phases with different styles of carpentry. The north leaf (with wicket) was thought to be 14th century but this work shows that it is a C17th replacement; the possibly original south leaf failed to date. The keep is a four-storey residential tower, now unroofed, in which the upper floors were annexed to the adjoining Castle House. sampling of a first-floor timber fireplace beam showed that the keep had been refitted in the 16th century.
Hay Castle House is a large C16/C17th house built within the medieval castle site and serving as the post-medieval manor-house. The house has a double-pile plan, three-storeyed with shaped attic dormers on the seven-bay main front, and impressive clusters of brick chimneys. The timber spine-wall separating principal rooms from stair and service-rooms was revealed by the disastrous fire of 1977 which destroyed the roof. Nevertheless, some good C17th detail survives including ogee mouldings on the timber partition and beams, and distinctive stone ball-finials on gateposts and dormers. The great Jacobean stair (photographed by Country Life) was destroyed by fire. The doorcase on the north terraced garden side survives. Reanalysis of samples taken by Martin Bridge from the fire-damaged roof timbers shows that the house achieved its mature form in the early C17th. The site is assessed in R. Haslam, The Buildings of Wales: Powys (1979).