The building sits at the north-eastern edge of Church Island, oriented roughly north-west to south-east, and its walls, though surviving to only about a metre in height, are double-faced with a rubble and earth core and measure between 1.5 and 1.8 metres thick. What makes the structure quietly remarkable is not its scale but its detail: the rounded external angles, a pair of opposing doorways through the end walls, and the remnants of a floor surface made up largely of compacted shells and bone, the accumulated debris of daily meals.

Archaeological evidence places this rectangular building later than a circular stone house at the centre of the island, suggesting the site was occupied across more than one phase of construction and use. The house measured 5.15 by 3.8 metres internally and was roofed with a timber frame carried on fifteen posts, thirteen arranged around the perimeter of the floor and two in central positions. The posts flanking the doorways appear to have doubled as door frames. A hearth containing peat ash occupied the interior, and along the base of the southern wall a slab-lined pit was cut into the floor specifically to collect water, fitted with an overflow drain, a modest but carefully considered piece of practical infrastructure for island living.

The floor deposit of shells and bone is particularly evocative. In the absence of written records, such material gives a direct, unglamorous account of what people were eating and how a space was actually used over time. The peat ash in the hearth points to the fuel source available on and around the island, and the whole assemblage together, walls, posts, pit, and floor, allows an unusually legible reading of a building that would otherwise be easy to walk past as just another low run of stone.