Built from random rubble, the structure was rendered and painted to mimic ashlar, the finely cut dressed stone associated with wealth and permanence. The effect, in its day, would have been convincing enough: a castellated mansion with a complex ground plan, numerous projecting towers, and a north-facing doorway flanked by further towers. The large window openings carry mullions, tracery, and hood-moulding, the kind of decorative stonework that frames and caps windows to deflect rainwater, all the architectural vocabulary of Gothic Revival ambition compressed into what was, structurally speaking, a rather more modest construction.

The house was built by John Coltsman between 1809 and 1815, a period when the castellated style was fashionable among Irish landowners who wished their properties to suggest antiquity and solidity. The choice of render painted to resemble ashlar was not unusual for the era, but it does give Dromhumper a slightly theatrical quality, a house performing a grander version of itself. The wider estate had the expected supporting cast: an enclosed farmyard lies roughly 400 metres to the south-east, and an ornamental tower stands approximately 300 metres to the north-west, the kind of eye-catching folly designed to be glimpsed across the grounds and lend the landscape a sense of romantic composition.