The building, recorded as Structure 9, survived only because the inner terrace of the enclosure wall had effectively buried it, protecting it from the stone-robbing that stripped away the rest of its wall circuit. What remained was a carefully constructed arc of walling roughly 1.9 metres long, made up of five upright slabs wedged tightly together with packing stones filling the gaps.

The projected outline of the house suggests a circular building with an internal diameter of around five metres, a modest but practical dwelling form common in early medieval Ireland. No clear occupation surface survived, but the layer between the floor level and the ground beneath it preserved a telling scatter of everyday life: animal bone and limpet shells from meals, fragments of cooking ware, a bone point, an amber bead, a clay mould fragment, and two corroded iron pieces. Most evocative were the finds from the northern part of the floor area: an early medieval bone comb and a fragment of a second one, objects used for grooming or textile work that speak to the small domestic routines of whoever lived here. The site was one of four possible house structures uncovered in the same excavation, suggesting that at some point people were not merely visiting Dún Aonghasa but living within its walls. A hoard of Late Bronze Age buffered rings, objects that pre-date the medieval occupation by well over a millennium, was found roughly 1.35 metres to the south-west, a reminder that the layers of activity at this site are considerably more compressed and complex than the fort's dramatic exterior might suggest.