2006:586 - CORBALLIS: Corballis House, Dublin

Test excavation and monitoring was carried out on the proposed site of a new terminal building at Dublin Airport. The works on site included the monitoring of geotechnical site investigations, monitoring the removal of plaster render from Corballis House and the excavation of test-trenches around the site of Corballis House and within the constraint area of a ‘castle site’ (DU014–011).

Nothing of archaeological interest was uncovered during the monitoring of the geotechnical site investigations. The test-trenches indicated that a layer overlying subsoil consisted of made ground containing a mix of clays and post-medieval artefacts, including red brick, modern glass, wood and post-18th-century pottery. The area has been levelled in recent times and resurfaced as a carpark.

Test excavation adjacent to the castle, described as a ‘castle in ruins’ on the OS maps, focused on establishing if any remains survived subsurface. The test locations in this area were confined to the grassy margins, as the remainder of the areas function as existing airport catering facilities, aircraft hangars and car parking bays. Unfortunately, as uncovered in Trenches 1 and 2, an extensive network of services supply the surrounding buildings. Trenches 4–6 were halted at varying depths above active service conduits supplying power, heating and telephone services to the existing airport buildings. As a consequence, the soil profiles in many instances consisted of modern landscaped ground over backfilled trenches.

At the eastern end of Trench 3, natural ground at 0.4–0.5m was located below present ground level. It lay directly beneath a layer of made ground that included plastics and other modern material. There was no evidence of a buried sod horizon, suggesting that the ground was scarped and levelled in this area. Much of the surrounding area is occupied by buildings and roads.

Trench 9 uncovered a post-medieval field ditch, suggesting that elements of the old ground surface still survive in places. As a consequence, it was recommended that an area measuring 50m by 50m centred on the site of the ‘castle’ as marked on the OS maps be opened as an archaeological exercise in advance of the development proceeding.

The architectural investigations and opening up works at Corballis House were undertaken to assess the structural stability of the house and to examine the fabric of the walls as part of a condition survey. In addition to the removal of plaster render, the opening up works involved the excavation of two test-pits around the foundations of the house.

Test-trench 1 measured 0.9m along the north–south rear wall of Corballis House. It was 0.85m wide (east–west) at the base and was excavated to a depth of 1.2m below the existing ground level. The trench revealed that the foundation of the rear wall of Corballis House extended 0.76m below the existing ground level. This wall was built upon a shallow narrow foundation plinth, 0.22m deep. The plinth was set 0.05m out from the line of the wall and had a slight basal batter. A cobbled surface extended from the foundation plinth, 0.96m below the ground level, laid above the boulder clay. The cobbling (measuring 0.06 by 0.07m by 0.04) included fragments of red brick in its fabric. A shallow depression/drain was present in the cobbles, indicating that water drained along the axis of the house wall. A fragment of an 18th-century wine bottle and a single sherd from a blackware milk pot were recovered from the green sandy clay fill above the cobbles, indicating that the cobbling dates from at least the late 18th/early 19th century. Various other rubble drains and pits were located in the upper 0.6m of the trench. The wall revealed in section was a roughly coursed limestone masonry wall. The boulder clay consisted of a compact and stiff blue/brown natural boulder clay mixed with gravel.

Test-trench 2 measured 1m north–south by 1.2m and was excavated to a depth of 1.15m below the existing ground level. The trench revealed a rectangular sectioned foundation set 0.16m out from the external line of the house wall. The foundation was roughly coursed (with three courses) and was constructed from stones measuring c. 0.15m by.015m to 0.16m by 0.28m. Red brick was occasionally used in the fabric of the foundation. The foundation was 0.43m deep and was identified 0.4m below the existing ground level. The foundation was built upon a compact and stiff blue/brown natural boulder clay mixed with gravel.

Plaster render was removed from key surfaces at Corballis House. The removal of plaster render from the building confirmed the suspicion that an earlier structure was contained within the later extended late 18th/early 19th-century house. This early building appears to be a simple rectangular stone structure; it is likely to have functioned as a dwelling and appears to be the structure illustrated on the Down Survey map in the mid-17th century.

The definitive identification of the c. ad 1600 building is based upon a number of observations. The floor level in the rear kitchen of the house is lower than the floor in the remainder of the building, such as the hall and bow. There is no obvious explanation why this would be so if the building dated principally from the late 18th/early 19th century. The ground plan of the house is unusual and irregular and suggests that the building was constructed sequentially; the unusual ground-floor plan is reflected in the plan of the roof. The wall fabric in the rear house wall is exclusively fashioned from limestone masonry. The wall fabric in the front façade and in the hexagonal bow (adjacent to Test-trench 2) is made from combinations of masonry and red brick. The differential fabric of the walls suggests that these elements of the house belong to two separate phases within the building’s history. Clearly the bow, with its decorative plasterwork, is late 18th/early 19th-century in date. Accordingly, the rear walls are likely to be earlier.

The main dating evidence for the earlier structure is based upon the chamfered masonry identified when plaster render was stripped from the external face of the rear house wall. These architectural fragments, when considered in combination with the wall thickness, suggest a building that dates from the early post-medieval period (c. ad 1600). The building is also illustrated on Rocque’s map of 1760, before it was extended in the late 18th/early 19th century. It is possible that the chamfered stone has been taken from another building, the most likely candidate being the castle site (DU014–011).

The early elements of Corballis House that have survived extensive remodelling are fragmentary and hidden within the later fabric of the building. There is no record of an earlier building in the National Inventory of Architectural Heritage report on the house. The walls of the earlier building appear to survive to roof level, where they have been incorporated into the present house. Further opening-up works will establish this for certain.

27 Merrion Square, Dublin 2