Buried under layers of re-deposited natural soil in an area designated Trench N, the remains of an earlier building, recorded as Structure C, turned out to be not a house at all, but most likely a place of industrial work, possibly for drying grain. Three shallow, bowl-shaped pits cut into a raised floor surface each contained dense charcoal-rich soil, and their bases were covered in red and orange oxidised earth, the signature of sustained, high-temperature burning in place. Thirty-six stake-holes encircling these features suggest that timber and wattle superstructures once enclosed them, perhaps acting as the housings for corn-drying kilns, a type of small agricultural furnace used to dry harvested grain before milling or storage. Carbonised wheat was recovered from one of the pits, with smaller quantities of rye and cereal chaff found across all three.

The excavations at Carrickmines were carried out under licences 00E0525 and 02E1532, and the findings were compiled by T. Breen in a 2012 report prepared on behalf of Dún Laoghaire-Rathdown County Council in connection with the M50 south-eastern motorway scheme. Structure C post-dated an earlier phase of occupation on the site, known as Structure B, which is interpreted as belonging to the first period of medieval settlement at Carrickmines. The gullies defining the perimeter of Structure C on its western, southern, and eastern sides were wide and shallow, over a metre across in most places, and one contained a smooth cobbled surface with a step feature. This unusual profile led excavators to initially doubt that they were wall foundation trenches at all. If they were, the building appears to have had only three enclosed sides, open to the north, an arrangement that would suit an industrial rather than a domestic function. The structure is thought to have been broadly contemporary with a horizontal mill recorded nearby in Trench 10, and with Structure D some five metres to the north-west, which is interpreted as a domestic building and may have been associated with Structure C in the same working complex.

Structure C is no longer visible on the ground; the excavated area was recorded and the site subsequently developed as part of the motorway infrastructure. The archaeological record survives in Breen's 2012 report, published in four volumes, which remains the primary source for understanding the sequence of medieval buildings at Carrickmines. For those interested in engaging with the material, the National Monuments Service holds the relevant records, and the site reference DU026-005001- can be used to locate associated entries in the Sites and Monuments Record for County Dublin. The finds themselves, including the carbonised grain, offer a rare and specific glimpse into the agricultural economy operating in the shadow of a medieval castle before its defensive enclosures were even built.