23 Clarendon St, Londonderry

23 Clarendon Street, Londonderry is a mid-terrace, two-bay three-storey townhouse with attic over basement, built in 1862–63 in Georgian style to match the adjoining houses at nos 25–27 (built 1853–56). It forms part of a row of twelve similar early to mid-Victorian townhouses lining the south side of Clarendon Street, within the Clarendon Street Conservation Area.

The building is rectangular on plan with a projecting rear return. The principal north-facing elevation sits behind a low rendered wall with painted stone coping and replacement black painted metal railings. Access to the front entrance involves five steps up, with the bottom two steps projecting beyond the boundary wall onto the pavement.

The principal front elevation is constructed in Flemish bond red brick with a rendered basement terminating at a string course at ground floor level. The entrance doorway features a three-centred-arch opening with moulded cornice supported by Doric columns, framing a painted timber four-panelled door beneath a single-pane overlight. All window openings are square-headed with painted cement-rendered reveals and painted sills. The fenestration comprises 6/6 timber sliding sash windows throughout, arranged as two diminished windows to the left of the door, with two windows each to the first and second floors (these upper windows are not aligned with the ground floor openings). Two casement windows serve the basement level, positioned directly below the ground floor windows.

The pitched slate roof carries a single rear dormer and black clay ridge tiles. A large brick chimney stack rises from the east side, centred on the ridge with seven clay pots. Cast-iron guttering and circular downpipes front the property.

The east and west elevations are abutted by adjoining buildings at nos 21 and 25 Clarendon Street respectively.

The south (rear) elevation is cement rendered and comprises a three-storey main block with attic over basement, together with a cement-rendered pitched-roof four-storey rear return (over basement) to the left, and a small single-storey lean-to boiler house to the right. The right bay of the main block features a modern uPVC door with sidelights to the basement and single 6/6 timber sliding sash windows to ground, first and second floor levels, topped by a pitched roof timber-clad dormer with a single 6/3 timber sliding sash window. The left bay is fully abutted by the rear return.

The rear return's south gable exhibits irregular fenestration: a single casement window to the basement, a single 2/2 timber sliding sash window to ground floor, and a canted timber oriel window to the first floor comprising margin-paned timber sliding sash windows (2/2 round-arched, 4/4 segmental-arched, 2/2 round-arched). Two diminutive 1/1 timber sliding sash windows serve the second floor, with a 6/3 timber sliding sash window to the third floor. The east face has a flush fire door to basement level, a diminutive 1/1 timber sliding sash window to the first floor, and a round-arched margin-paned timber sliding sash window to the second floor; upper floors were not visible at survey. The west face is blank.

At the rear of the site stands a two-storey pitched natural slate-roofed whitewashed stone mews building with brick dressings. Its north elevation has a vertically sheeted timber door left of centre surmounted by a square-headed three-pane overlight, with two square-headed timber louvered openings to the first floor. The east elevation is blank. The west elevation is fully abutted by the mews building of no. 25 Clarendon Street. The south elevation has a square-headed timber louvered opening to the first floor left and a vertically sheeted timber opening to the first floor right; the ground floor was not visible at survey.

Materials include slate and cast-iron guttering to the north-facing roof, with uPVC guttering to the south. Walls combine brick and render. Windows are timber throughout the north and south elevations, with uPVC panels to the south elevation.