The building, roughly seven metres across in both directions, is set directly on the fosse, the defensive ditch, of an older enclosure, and its eastern wall is not newly built at all. It is simply the pre-existing outer wall of that enclosure, pressed into service as part of a later dwelling. Whoever constructed this house was not starting from scratch; they were working with what the landscape had already provided.

The site at Drumharsna belongs to a small cluster of related structures. A similar house site lies to the south, and a further one occupies the interior of the enclosure itself, suggesting that people returned to this spot across time, finding the old stonework useful rather than sacred or untouchable. The building material is large slabs and boulders set on edge, supplemented with smaller stones, and the whole thing is now grass covered, which softens its outline considerably but does not entirely dissolve it. The date of construction is genuinely unknown, which is itself worth pausing on. Not every ruined structure yields its age, and the honest designation of indeterminate date is a reminder that the Irish landscape contains a great deal of human activity that resists neat chronological labelling. What can be said is that someone, at some point after the enclosure fell out of use, looked at its fosse and outer wall and saw the bones of a serviceable home.