40 Clarendon Street, Londonderry, County Londonderry, BT48 7ET

40 Clarendon Street is a mid-terrace, two-bay, three-storey townhouse with an attic over a basement, built in 1864 in the Georgian style using red brick. It forms part of a row of eleven similar houses lining the north side of Clarendon Street, and was constructed at the same time as the adjoining numbers 38 and 42–44. It shares group value with numbers 6–38 and 42–48, which were built over an eight-year period. The house retains much of its original character and detailing, and is situated within the Clarendon Street Conservation Area, whose well-preserved setting adds further to its interest.

The building is rectangular on plan with a projecting rear return. Its principal elevation faces south onto Clarendon Street and sits behind a low cement-rendered wall with a concrete coping and replacement painted metal railings. The pitched slate roof has black clay ridge tiles to both the main roof and the rear return, with a large red brick chimney stack rising from the east side, centred on the ridge and fitted with clay pots. Cast-iron guttering and a circular downpipe serve the front elevation.

The principal south-facing front elevation is laid in Flemish brick bond. All windows are two-over-two timber sliding sashes set within square-headed openings with painted cement-rendered reveals and painted sills. The entrance doorway has a three-centred arched opening with a moulded cornice supported by columns of the Doric order on plain pilasters to either side, enclosing a painted four-panel fielded timber door with a plain fanlight above. There is a single window to the right of the door at ground floor level, and two windows each at first and second floor level, though the upper-floor openings are not aligned with those on the ground floor. The east and west sides are abutted by the adjoining numbers 38 and 42 respectively.

The north rear elevation is finished in unpainted roughcast render and rises three storeys over a basement. A three-storey-over-basement unpainted roughcast rendered rear return stands to the right, built at half-landing height and surmounted by a casement window. The left bay of the rear elevation has a modern timber door with glazed top and bottom panes at basement level, and single six-over-six timber sliding sash windows to the ground, first, and second floors. There is a single rooflight to the left-hand side of the rear slated pitched roof. The north face of the rear return has a single casement window to the right of centre at first and second floor level; the remainder of this elevation was obscured at the time of survey. The east and west faces of the rear return were not visible at the time of survey.

The property is approached at the front from Clarendon Street across substantial granite flagstones leading to the principal entrance door. A yard to the rear is accessed through a large square-headed opening in the rear boundary wall, and a laneway running along the back of the site provides access to the rest of the terrace.

Clarendon Street was laid out in the early Victorian period as part of an ambitious programme of urban expansion beyond the historic walled city of Londonderry. The first edition Ordnance Survey map of 1830 shows the Clarendon Street area — in the townland of Edenballymore — as rural hinterland, with the city's streets at that time extending no further than Waterloo Place, Abbey Street, and William Street. The only significant buildings north of the walls in the early 19th century were isolated institutions such as the Londonderry Infirmary, the Lunatic Asylum, and Foyle College. The sole domestic building of note predating the Victorian development is Foyle Cottage, a Regency house of around 1815. Robert Simpson, writing in his Annals of Derry (1847), recorded that the area that would become Great James Street, William Street, and their surroundings had originally been open meadow ground without a house.

The development of this part of the city was driven by significant growth in both the economy and population of Londonderry during the mid-19th century, as described by John Hume, who notes that between 1825 and 1850 reconstruction within the walls occurred alongside the first development of housing outside them at Bogside and Edenballymore. The new streets — Clarendon Street, Great James Street, and Queen Street — followed a geometric pattern characteristic of Georgian town planning, representing the most ambitious planning project in Londonderry since the construction of the walled city between 1613 and 1619. With their uniform rows of neat three-storey townhouses, these streets quickly became home to the city's merchant and professional classes.

A plan of Londonderry dated 1847 shows the proposed layout of Clarendon Street — then known as Ponsonby Street, after the Rt. Rev. Richard Ponsonby (1772–1853), Bishop of Derry and Raphoe — at least a decade before the street was completed. By the 1850s it had been renamed Clarendon Street in honour of George Villiers (1800–1870), the Fourth Earl of Clarendon and Lord Lieutenant of Ireland from 1847 to 1852. The second edition Ordnance Survey map confirms the new name was in use by at least 1853.

Although the 1847 plan showed Clarendon Street extending from the quay up to Francis Street, only the lower section between the Strand Road and Queen Street had been laid out by 1853. Development progressed slowly through the 1850s: in 1851 Skipton and Miller had advertised building ground on Clarendon Street, Queen Street, and Patrick Street to be let in perpetuity, and Griffith's Valuation of 1856 recorded only nine dwellings along the entire length of the street. Additional leases for building ground on the north side were advertised in 1856.

Number 40 was built in 1864 as part of the second phase of Clarendon Street's development, constructed along with the adjoining numbers 38–44 for William McIlwee, a carpenter and builder with business premises on Foyle Street, as recorded in the Ulster Town Directories. In 1864 the property was originally valued at £27 in the Annual Revisions. By 1901 it was occupied by Rebecca McPherson, described in the census as a house mistress living on investment income; her house was classified as a first-class dwelling comprising ten rooms. Ownership had passed to a Mr. Frances McPherson in 1888, and by the 1930s a Mr. John H. McCrea was recorded as owner under the First General Revaluation of Property in Northern Ireland. By the end of the Second Revaluation (1956–72) the property's value stood at £60 10s.

In 1969 the building was converted from a private dwelling into self-contained flats. In 1978 the Department of the Environment designated Clarendon Street and the surrounding streets a Conservation Area, defined as an area of special architectural or historic interest whose character it is desirable to preserve or enhance. Number 40 was listed in 1979. A photograph taken in 1978 records that the property had a modern dormer window to the front, which has since been removed. In 2000, according to Northern Ireland Environment Agency Historic Buildings records, the building was converted into offices, a use it continued in at the time of the second survey.

Writing in 2013, Calley described numbers 6–48 Clarendon Street as a "delightfully long red brick terrace of the mid-19th century," noting that the buildings are "nearly all the same, being three-and-a-half-storey, two-bay with most ground floors rather inelegantly squeezing in a doorway with two reduced scale window bays," and that "depressed arched recessed timber-framed doorways have simple segmented fanlights and thin Doric columns supporting entablatures." Few of the mid-Victorian townhouses along Clarendon Street now remain in residential use; the majority were converted into offices for dentists, solicitors, and accountancy firms during the late 20th century.