The building is roughly 8.3 metres in external diameter, constructed from diorite that appears to have been quarried from the island's own high ground, and the doorway, a modest 0.6 metres wide, faces north-east. The Office of Public Works rebuilt much of the door jambs at the turn of the twentieth century and added a concrete capping to the wall, so what stands today is partly conservation-era work laid over genuinely ancient fabric.

What makes this building particularly legible as a lived-in space is the quality of the archaeological evidence recovered from its floor. The uppermost layer was a thick deposit of carbonised organic matter, interpreted as burnt thatch, with large iron nails embedded within it; beneath that lay a trampled surface of habitation refuse that spread through the doorway and out towards the north-east edge of the island. The material was ordinary and telling in equal measure: shells, animal and fish bones, peat, carbonised grain, a rotary quern for grinding, a net sinker, and several iron knives. A substantial hearth near the doorway held peat ash and more shells and bone. Against the south wall, a cluster of small post-holes suggested a raised seat or sleeping platform. A small drain, covered with slate slabs, ran from the interior out through the doorway, a detail that speaks to some concern for managing water or waste within a confined space. Roof timbers rested on twelve evenly spaced posts set around the perimeter of the interior, two of them flanking the door. After the house was built, a low ring of roughly laid stonework was added around its external base, apparently to hold a turf mantle in place as insulation against the Atlantic wind and damp.