South-west Farm Building at Mostyn Hall Farm

This is a long, two-storey range with a projecting gabled block to the right of the centre, built of rubble stone and covered by a slate roof with raised copings to the gables. An entrance to the upper storey is on the north-west side of the gabled block; it consists of a wide opening with a segmental arch of stone voussoirs leading to stone steps. A boarded door, with an overlight above, is to the left, and two narrow, stone-lined windows are above. The gable end has a two-light stone mullioned window to each storey. A similar window is on the south-east side, but is infilled with brick, to the right of which is a reduced chimney stack. A lean-to extension is against the lower storey, with a door and window, and a boarded opening with a segmental brick head at the end.

The main range flanking the gabled block has two-light stone mullioned windows to the upper storey, with six windows to the left and four to the right. Alternate windows are blocked with brick, the others fitted with glazing and louvres. There is evidence of alterations to the lower-storey openings, most of which are boarded doors under segmental arches of stone voussoirs. To the far left is a two-light boarded window with a timber lintel, filling the space of a former doorway. A stable door is followed by a window, then a further stable door flanked by ventilation slits, and a boarded hatch. A short wall extends at a right angle to the left, with an infilled doorway. To the right of the gabled block are three boarded doors; the third has a timber lintel, and there are blocked ventilation slits. The jambs of earlier openings are also visible. The north-west gable end abuts a later farm building.

The rear side has a recessed first-floor doorway, offset to the right, flanked by stone mullioned windows as on the front elevation; there are five to the left and two to the right. Three of these windows are infilled with brick, and the mullion is missing from the first and third windows on the left. The lower storey has a blocked doorway to the far left, two doorways as on the front, window openings with stone voussoir heads containing louvres and ventilation slits. An infilled window opening is on the south-east gable, below which is an added single-storey unit with an attic, likely adapted in the mid-19th century as a weighbridge house and listed separately.

Inside, a staircase leads to a small room in the advanced gabled block, divided by a box-framed partition, and featuring a shaped timber doorhead. The room is plastered and includes a small fireplace. In the main range, the upper floor is missing, but large cross-beams remain.