Dunderg House, 276 Drumcroon Road, Coleraine, BT51 3QT

Dunderg House is a detached, symmetrically planned three-bay residence set over a basement, with Georgian origins and substantial later alterations. The main block was constructed around 1840 as an extension to an earlier late eighteenth-century house, and was significantly remodelled around 1870. The building is T-shaped in plan, facing southeast, and formerly had an additional lower wing of eighteenth-century origin to its north, which was demolished around 1970. A three-storey stair tower now abuts the centre of the rear elevation, with a steel and uPVC conservatory to the southern re-entrant angle.

The exterior is rendered in painted cement with a pitched roof carrying replacement natural slate and clay ridge tiles. Two rendered chimneystack pairs sit symmetrically on the roof. Replacement steel rainwater goods and fascia complete the upper works. The front elevation displays six regularly spaced square-headed window openings with painted masonry sills, fitted throughout with uPVC windows. Three staggered basement window openings occupy the north end. A central entrance porch projects forward, with a shallow pitched roof and an elliptical-headed door opening. The doorcase is modern timber with a replacement fanlight, flanked by fixed-pane sidelights repeated to each cheek and framed by Doric corner pilasters supporting an entablature enriched with triglyphs and a diminutive depressed pediment. The door opens onto a stone-flagged area within the gravel forecourt.

The gabled side (south) elevation is two windows wide and abutted by a central canted bay window with flat roof. The rear elevation shows irregular fenestration including a single round-headed window opening with leaded coloured glazing. The three-storey gabled side elevation to the north has a single window and door opening to the right at basement and ground level, with a sheeted timber door to the basement.

Historically, the site was the location of Greenfield House, a linen mansion built in 1785. The original structure and its associated bleach green were documented in the first edition Ordnance Survey map of 1830, situated beside the Macosquin River. The house was the seat of Stephen Bennett, a linen merchant and proprietor of Macleary bleach green. The Ordnance Survey Memoirs of 1835 describe it as "small and…highly ornamented in front, particularly by many creeping plants and shrubs" with a pond in front containing an island, a temple, and swans, approached by an extensive and well-planted avenue. Bennett improved the house in 1820 and also built himself a summer residence at Portrush in the 1830s known as Seabank. Following Bennett's death in 1861, the property passed to his wife Frances. The house and its grounds, comprising over 76 acres, was listed in Griffith's Valuation of 1856–64 at £25 and was leased from Thomas Richardson. In 1868, James Sinclair took over the property and commissioned the new three-storey wing in 1869, whereupon the valuation rose to £45. At the 1901 census, the house was occupied by Catherine Sinclair, a widow living on income from land, with three adult children and a grandson, supported by a staff of nurse, cook, parlour maid and housemaid. The twelve-room house was designated first class. The property subsequently passed to Catherine's son, Robert A Sinclair, a land agent, and thereafter to successive tenants. Valuer's notes from the 1930s record the accommodation as kitchen, scullery and pantry in the basement; hall, two reception rooms and bathroom on the ground floor; and four bedrooms, a lumber room and WC on the first floor. The house was then lit by oil lamps, with water supplied by rainwater tanks and sewage draining to the nearby river.

The building stands at the end of a long bitumac avenue to the west of Drumcroon Road, shared with two neighbouring properties. The landscaped grounds contain mature trees and a walled garden to the southwest. Rubblestone castellated garden walls to the west and north are lined on their inner sides with red brick laid in English garden wall bond, including matching castellations. A small paved yard to the rear is enclosed by a single-storey over basement rubblestone outbuilding with a brick vaulted wine cellar, abutted by the garden wall which features a double-height brick arch surmounted by stone ashlar coping forming a double ogee. To the west of the site, a small river is crossed by a track leading to a former yard and the north side of the house. A pair of spear-headed wrought-iron gates, hung on lime-rendered stone piers with conical capstones, marks the entrance to the property.