Cart shed at Castle-upon-Alun House

The cart shed at Castle-upon-Alun House is a long, single-storey building dating from the 19th century, oriented east-west. It is constructed from rubble stone and covered with a slate roof. The south-facing front features four wide basket-arched openings with voussoirs. The second and fourth openings from the left have been blocked with masonry. The blocking of the second opening includes a 4-pane window with shutters and no glazing, set on a brick sill. The fourth blocking has a low opening at ground level. Originally, there was an additional range to the west, which is now in ruins. There are no openings on the rear side of the building.

The east gable end has another wide opening at a lower level, which is filled with brick beneath the arch. Above this opening is a loft hatch with a brick surround and shutters. Inside, there is a rubble stone partition between the third and fourth bays from the left, with openings on either side. Steps to the right would have led up to the loft in the eastern bay. There is also a small square opening in the center, possibly for a chute. The structure features simple tie beam trusses.