A subrectangular building, uncovered during excavations and conservation works carried out on the island from the mid-1990s through to 2002, does not fit neatly into the expected pattern of monastic architecture. Its walls survive to a maximum height of only 0.4 metres, built with stone faces enclosing a rubble core of clay and stone, and both the west and east walls are splayed outward, giving the plan a slightly irregular, widening form. Entrance was not through a purpose-built doorway but via a passage broken through the wall of the monastic enclosure itself, which served as the building's southern boundary.

The structure was built leaning against the annulus, the ring-shaped enclosing wall, of a feature known as Cell A, and against the western end of the northern wall of the wider monastic enclosure. An annulus of this kind typically surrounds an early ecclesiastical cell or oratory, suggesting this building was added at a later stage, making use of existing boundaries rather than being part of any original design. Inside, the only features found were two small post-holes in the north-western area of the floor. The excavators noted that these holes were too slight to have held posts capable of supporting any substantial roof structure, which leaves the function of the building genuinely uncertain. Whether it served as a work space, a storage area, or something else entirely, the evidence does not say.