Hayes Farm Windmill Sully · Vale of Glamorgan · Wales

Hayes Farm Windmill stands at Sully, between Hayes Road and the industrial estate, opposite Hayes Farmhouse and north of Sully Hospital. It formed part of Hayes Farm, a model agricultural complex built in 1813 by Evan Thomas of the Llwynmadog Estate, Brecknockshire. Thomas had bought the manor of Sully in 1812 and modernised the area's agriculture according to best practice of the period. Seven farms were reorganised into two model complexes, Cog Farm and Hayes Farm, managed by bailiffs, with larger fields and improved facilities.

Unusually for farms of the period, Hayes and possibly Cog had their own windmills to grind corn. Edward Harrie and William Stoddard were recorded as millers between 1821 and 1828. Hayes Farm Windmill was a stone tower mill of the revolving-cap type. It was later enhanced by a horse walk and gearing, and an oil engine was installed about 1902, extending the functional life of the complex beyond wind power alone.

The windmill tower is built of coursed rubble limestone with patches of render. The cap is missing, but iron joists from a former gantry survive at about two-thirds height, with a blocked access opening on the north side. Windows and doorways survive on the west, east, and south sides. The south door opens at first-floor level into the attached granary. The granary and barn form a long rectangular roofless range of rubble stone with red-brick dressings, including former two-storey accommodation with a granary to the west and barn to the east.

The interior makes the site especially important. The tower retains a hurst frame, two pairs of stones and stone nuts, a complete drive post with wallower and spur wheel, and another drive passing through the wall. Hayes Farm Windmill was listed at Grade II on 16 April 1996 as the only windmill in South Wales known to retain surviving machinery and for the historical interest of the model-farm complex created during early nineteenth-century agricultural modernisation.