Gillbrook, 1 Mullaghcarton Road, Magheragall, Lisburn, County Antrim, BT28 2TB

Gillbrook is a detached three-bay two-storey house with attic, built around 1850 in stone and brick. It stands at a rural crossroads south of Mullaghcarton Road in Magheragall, with its east gable facing onto Cross Lane. A single-storey stone wing in L-plan extends to the west, formerly the house stables. The building exhibits the character and aspirations of a nineteenth-century rural holding through its symmetrical front elevation, exposed stone construction and modest proportions. Despite modern additions including dormer windows to the rear and a lean-to conservatory, the house retains many original features and contributes significantly to the heritage of the area.

The main house is rectangular on plan, with a pitched natural slate roof fitted with roll-moulded terracotta ridge tiles. Redbrick chimneystacks rise from both gable ends. The walling consists of squared uncoursed rubblestone with squared quoins and redbrick surrounds to all openings. Cast-iron guttering on iron brackets runs above a redbrick eaves course, with cast-iron downpipes.

The symmetrical north front elevation is five windows wide with a central square-headed door opening. The door comprises a moulded stepped architrave surround on plinth blocks and a flat-panelled timber door with rectangular overlight, opening onto a footpath to the front garden. The window openings are square-headed with rendered reveals and painted masonry sills; most are now fitted with replacement 6/6 timber sash windows. The east side elevation has a single first-floor window and two diminutive attic windows, now with uPVC replacements. The redbrick chimney flues create an equal stone-to-brick ratio in the walling. A rubblestone boundary wall encloses the gable facing Cross Lane.

The south rear elevation is three windows wide, abutted by a lean-to glazed conservatory and incorporating three flat-roofed dormer insertions to the rear pitch. A replacement tripartite timber sash window occupies the ground floor, with uPVC windows to the remainder including the dormers. The west side elevation is abutted by the single-storey wing, which has a ground-floor door opening and two attic windows.

The L-plan former outbuilding has a pitched natural slate roof and rubblestone walling. Square-headed window openings contain replacement timber sash windows to the connecting north section, steel casement windows to the west section, and replacement timber sheeted doors opening onto the gravel rear access lane.

The setting is prominent. The house faces north on a corner site enclosed by tall rubblestone walls. To the east, a tall rubblestone wall with iron sheeted gates on stone piers opens onto Cross Lane. To the north, a low rubblestone wall with stone coping encloses the front garden, with a pedestrian iron gate on brick piers opening onto Mullaghcarton Road. To the west, a vehicular opening with modern steel gates and a gravel drive runs along the attached wing. The house sits north of a stone railway bridge crossing Cross Lane.

Historically, Gillbrook first appears on the second Ordnance Survey map for the Magheragall area (1857), depicted as an oblong building at a crossroads west of Lisburn. The west extension is shown on that map as a separate rectangular outbuilding. In 1859, Griffith's Valuation records that the Marquis of Hertford let the house to Mr George Gill. The house and its office were valued at £14. George Gill occupied the property until his death in 1860, when his son John Valentine Gill inherited it. Between 1863 and 1865 the valuation was reduced to £11, though the reason is unclear. John Valentine Gill worked as a shopkeeper on the Newtownards Road in Belfast, while his wife Mary Agnes managed the farm at Gillbrook with their four children. The house was recorded as a first-class dwelling of six rooms. By 1901, the current extension had formerly served as a stable and also accommodated a calf house, dairy, piggery, fowl house, barn and turf house. John Valentine Gill died in 1910, leaving the house to his widow Mary, who occupied it until 1928. The connecting extension linking the house to the former stables post-dates the 1920 Ordnance Survey map but appears on the 1973 edition. A sun room was added by 1989. The house was listed in 1988. The listing extends to the house, outbuilding, boundary walls, piers and gates.