L-Plan range of outbuildings at Treginnis Uchaf

The building is an L-plan range of outbuildings at Treginnis Uchaf, constructed from rubble stone and originally featuring grouted slate roofs. Most of the structure is single storey, with two-storey sections at each end. At the northeast end, adjacent to the house, there is a two-storey symmetrical range with an asbestos roof. This section has a brick eaves course with dove-holes and a slate shelf, with two upper window heads interrupting the shelf. The windows below are similar, all originally small-paned, and there is a centrally located ledged door. The building features painted cambered brick heads throughout and has a plaque above the door stating, "Built by John Mortimer AD 1854."

The range continues to the left with a slightly lower roofline and similar dove-holes under the eaves. This section includes one door, three windows, another door, and two windows, with the last two windows obscured by a later lean-to. The roof has an 11-bay collar-truss design and a hipped southwest outer angle.

The southwest range mirrors the first half, featuring dove-holes under the eaves, one door with a vent loop on each side, and a window to the left. Beyond this, there is a two-storey section with a door and a central window, along with a boarded loft door above. The roofline is continuous, and the eastern end has external stone steps leading to the loft door, with an additional window to the left and a ground floor door set in a recess under the stairs.