Ynysfach Engine House

Blast engine house, 4-storey rectangular building of dressed blue Pennant sandstone with white-ashlared limestone quoins and dressings and hipped slate roof with deep eaves, in the house-style of the Crawshay ironworks. Windows have segmental heads with deep voussoirs and dressings, and small-paned replaced sash windows. N elevation has the main entrance through a round-headed arch approached by a modern stair, and one window above. The principal facade, to the E, is 4 bays long with equally spaced windows on 3 storeys, a semi-basement with round-headed arches, and cast iron brackets at the N end. The S end, facing the furnaces, has no windows. The W elevation has 6 irregularly spaced windows, cast-iron fittings, and a tall blocked archway at the S end.

Not accessible. Said to have new floors and partitions inserted, the bob wall for the beam engine passing through the centre of the building, and cast iron brackets for the engine''''s supporting structure and components visible in many places.