59a Old Mountfield Road, Omagh, Co Tyrone, BT79 7ET

Detached multi-bay one-and-a-half-storey house, formerly a stable block, built around 1875 and located on the north side of Old Mountfield Road, Omagh. This is the only remaining building from the former Knocknamoe Castle Estate. The house is well constructed in squared-and-snecked rubble stonework with tooled sandstone dressings, though it has been compromised by various alterations over time. The loss of the main castle house has also diminished its historic interest.

The building is rectangular in plan, comprising a three-bay house to the south with a coach house and store to the north. The roof is half-hipped natural slate with crenellated terracotta ridge tiles over brick cogged eaves. Three red brick corbelled chimneysstacks are present. Walls consist of squared-and-snecked rubble stone with stepped tooled sandstone quoins. Windows are largely replacement uPVC casements set within stepped tooled sandstone surrounds with projecting stone cills.

The principal elevation faces west. The three-bay house section contains a central replacement entrance door with a window to its left. Two pitched wall-head dormer windows occupy the attic storey—the left dormer features a wrought iron finial with the letter 'S' at its centre, believed to have been inserted by the Stack family. The right bay is blank. A single-storey west wing (the former stable block), also built around 1875, is abutted to the left of the coach house. Its exposed section shows a segmental-headed coach arch to the left, a square-headed timber sheeted door with transom light, and three square-headed loophole openings at attic level. The left (north) gable is abutted by a single-storey extension built around 1995, which forms part of a courtyard housing development to the north. This extension contains two attic windows flanking a central chimneystack.

The rear (east) elevation is partially abutted by a single-storey extension. Its exposed right section contains two original timber sliding sashes at ground floor, each protected by cast-iron bars. Two pitched wall-head dormers occupy the attic; the right dormer contains a replacement metal casement window with partially blocked opening, suggesting it originally held a timber sheeted loft door. The central dormer contains paired windows, and a third wall-head dormer at left features a flat roof. Various square-headed ventilation openings are present at ground floor and attic levels. The right (south) gable contains a blocked door opening to the right and a window to the left. Two windows occupy the first floor—the left remains as an original timber top-hung casement, though diminished in size.

A single-storey lean-to extension on the east, built around 1995, has a lean-to asbestos tiled roof, smooth rendered walling, and replacement uPVC windows. Its east elevation contains a replacement door to the right and a window to the left. A blank section appears at the left cheek, while the right cheek contains two windows, the left being diminished.

The single-storey west wing follows the detailed design of the main house. Its original door and window openings have been largely altered. The south elevation would originally have comprised three square-headed door openings—that at left is now blocked, while the two at right are now half-blocked and replaced with two uPVC windows. The original carriage arch to the right has been entirely blocked and now contains two replacement timber casement windows, though the arch timbers remain visible.

The house and west wing are surrounded by a cobbled perimeter. The north gable has been extended to provide a housing courtyard to the north, accessed through original entrance piers and incorporating the renovated west wing. The house is enclosed to the west by high squared-and-snecked rubble walling, with access via replacement cast-metal gates supported on square-plan roughly coursed sandstone piers with pyramidal coping.

These buildings were constructed as outbuildings of Knocknamoe Castle, first appearing on the third edition of the Ordnance Survey map in 1906 within the castle grounds. They are listed in valuations as part of the 'offices' of Knocknamoe Castle, entered into Annual Revisions in 1873, though a note of 1876 states the building was still 'unfinished'. Richard F. Stack was the original occupier, with George H. Stack as lessor. The property was valued at £82 10 shillings. Various occupiers succeeded until James Campbell became owner in fee in 1922. By 1935, valuers noted the castle was "a very large mansion house, built in 1875" with "very good situation in ornamental grounds" and town water and electrical installation. In 1941 the site was occupied by the military under defence regulations. By 1969 Knocknamoe Castle was in use as a hotel; it has since been demolished.

Historian Alistair Rowan suggested the castle may have been designed by Charles Lanyon, based on architectural details including the entrance porch with paired Tuscan columns and strapwork balcony, curly gables, and square turret with ogee copper cupola. Should this attribution be correct, the outbuildings may also be to Lanyon's design, though the design could alternatively derive from his pupil and assistant Thomas Turner. The outbuildings currently serve as a dwelling. Except for the adjoining west wing, the north courtyard was largely constructed around 1995.