Barn with attached cart shed at Berthymaen

This building is a rubble-stone barn with an attached cart shed, located at Berthymaen. It dates from the 19th century and is set on a sloping site, featuring a large stepped boulder plinth at the downhill end. The barn has a slate roof with coped gables.

At the front, there is a lintelled winnowing doorway that has been narrowed with brick jambs added to the right side, and it includes a boarded door. Flanking this doorway are three tiers of narrow ventilation strips, most of which are blocked with brick. A small lintelled opening is present at the right end. The left gable end, which is downhill, has a blocked lintelled opening that leads to the loft above the lower cart shed.

The cart shed, also constructed of rubble stone and topped with a slate roof, features two brick segmental-headed doorways with replaced doors, along with boarded loft openings beneath the eaves. There is a machinery store that is lower than the cart shed, which is open-fronted and supported by a central timber post, with added metal gates.

At the rear, the cart shed has two boarded loft openings. The barn includes a segmental-headed doorway leading to the threshing bay, where the jambs are original but the arch is from the 19th century, and it has a replaced boarded door. Above this doorway is an inserted loft opening, and to the right of it is a late 19th-century bearing box, likely added for steam-powered threshing using a portable steam engine. The doorway is flanked by ventilation strips similar to those at the front, which are mostly infilled. There is also a doorway at the left end, which is probably an insertion for a small stable, featuring a brick jamb on the right side and a boarded door. Additionally, a later large shed is attached to the uphill gable end.

The barn has a four-bay queen-post roof.