20 Clarence Avenue, Londonderry

No. 20 Clarence Avenue is a mid-terrace, two-bay, three-storey red-brick townhouse built in 1900 to designs by Robert Eccles Buchanan, a local architect and civil engineer active in Londonderry between 1887 and the 1920s. It forms part of a continuous terrace of eleven similar houses — Nos. 2–22 Clarence Avenue — lining the north side of Clarence Avenue on a steep gradient within the Magee Conservation Area. The street was originally laid out in 1897 and named in memory of Prince Albert Victor, the last Duke of Clarence and son of King Edward VII, who died in 1892 aged 28. The northern terrace comprising Nos. 2–22 was erected in 1900, as recorded in the Annual Revisions and reported in the Irish Builder of 15 January 1900.

The house is rectangular on plan with a projecting rear return built at half-landing level. It sits behind a low red-brick wall with painted metal railings above, set back from the pavement with a small front garden.

The principal (south) elevation faces onto Clarence Avenue and is finished in Flemish bond red brick. It is two bays wide. To the right, a two-storey canted bay rises through the ground and first floors and is surmounted at second-floor level by a rectangular gabled bay window cantilevered on large timber brackets with carved timber corbels to either side, finished with diagonal half-timber panelling to the gable and a plain, wide, painted timber fascia board. All openings are square-headed. The entrance doorway is reached by two steps up and features a moulded cornice supported on console brackets, with moulded pilasters to either side of a pair of fielded timber half-leaf panel doors with a stained glass square-headed fanlight above. All windows to the principal elevation are timber sliding sashes: 1/1 pane with stained glass upper lights to the canted bay at ground and first floor level and to the window above the door at first floor level; 8/2 panes to the box window at second floor level; and a single sliding sash with 4/2 panes above the entrance door opening at second floor level. There is a painted rendered band to the ground and first floor window heads, and a painted sill course to the first and second floor windows. Cast-iron guttering and circular downpipes serve the front elevation.

The east and west sides abut the adjoining Nos. 18 and 22 Clarence Avenue respectively. The north (rear) elevation is three storeys in height and is cement rendered with an unpainted finish. The two-storey rear return, built at half-landing level, has a small red-brick chimney rising from the gable end. This steps down to a single-storey duo-pitched abutment of smooth rendered, unpainted finish. Windows to the second floor of the rear elevation and rear return are timber sliding sashes with 2/2 panes; all floors below have timber casement windows, with uPVC casements to the abutment. A margin-paned sliding sash window is set within the west face of the two-storey return, overlooking the yard of No. 18. Within the yard, adjacent to the main house, a single-storey lean-to abuts the return to the adjoining No. 22; this is painted white and has a flush painted door with a glazed top panel to its north face. The ground floor rear return was extended in approximately 1995.

The main roof and rear return are covered in natural slate with terracotta clay ridge tiles. A large red-brick chimney stack with dog-toothed corbelling rises from the east side, centred on the ridge, with clay pots above. The rear elevation guttering and downpipes are a mixture of cast iron and uPVC.

The rear yard is bounded by smooth rendered walling with precast concrete coping, and contains a timber-sheeted painted gate within a square-headed opening. The yard backs onto a shared alley with the University campus beyond.

The leaded stained glass upper lights and half-timber work to the gable reflect a Late Victorian Arts and Crafts influence. Despite some replacement windows to the rear, the character of the original design survives in good measure.

Clarence Avenue was developed as part of the broader northward expansion of Londonderry, a process driven by economic growth and prosperity from the 1860s through to the end of the 19th century. Earlier phases of this expansion had produced Georgian-style terraces on Great James Street, Queen Street and Clarendon Street. By the 1860s–1870s, the Victorian terrace of Crawford Square was built when the area around Edenballymore and Northland Road was still largely rural in character. From the 1880s onwards, new red-brick dwellings at College Terrace and Clarence Avenue were erected to provide accommodation for students and staff of Magee College, whose campus was developed in tandem with the terrace.

No. 20 was initially valued at £26 and was first owned by a Mr Henry Thompson, with the house occupied by William Cunningham, a retired insurance agent. The 1901 census described it as a first-class dwelling of eleven rooms. By the time of the First General Revaluation of Property in Northern Ireland, the property had passed to the McCullagh family, who continued to live at Clarence Avenue until the 1970s. In the 1930s, a Mr James A. Thompson was recorded as owner, with the valuation having risen to £39. By the end of the Second Revaluation (1956–72) this had increased further to £44.

Buchanan was responsible for a number of domestic commissions in the city throughout his career, as well as church alterations including the repair of St Columb's Cathedral in 1911. The terrace as a whole has been praised by commentators: the Ulster Architectural Heritage Society described it as a "fine terrace" that is "excellently modelled", and Calley characterised Nos. 2–22 as a "generously proportioned terrace of eleven three-storey red brick houses" whose "second floors have oversized cantilevered box-like pedimented square bay windows resting on the bay window below and supported by robust timber brackets." The Magee Conservation Guide identified the dwellings along Clarence Avenue as representing "some of the city's architecturally finest and grandest townhouses" and noted the terrace as "very unified architecturally and virtually intact." The terrace was listed in 1979 and incorporated into the Magee Conservation Area in 2006.