15 The Diamond, Portstewart, Co. Londonderry, BT55 7EA

15 The Diamond is a two-bay one-and-a-half-storey end-terraced building constructed around 1880, now commercial premises but originally a residential house. It is located on the east side of The Diamond in Portstewart town centre and has group value with other listed buildings in the terrace.

The building has a rectangular plan with a two-storey return to the rear. The roof is pitched natural slate with blue and black angled ridge tiles. Rendered chimneystack with terracotta pots and bargeboards to the gables sit above the walling, which is painted smooth render. Plastic rainwater goods sit on projecting eaves.

The principal elevation faces west and is irregularly arranged. Three gabled dormers with 6/6 windows occupy the first floor, grouped more closely to the centre and right. At ground floor there is a 2/2 window to the right and a shop-front insertion to the left. The shop-front comprises a tripartite plate-glass window with timber jambs, flanked by panelled pilasters, with a continuous sill over a slate stall riser. A replacement four-panelled timber door to the right has a fixed timber transom and panelled pilaster. A plain fascia with cornice sits above. Windows throughout are replacement timber sash with projecting painted sills.

The north elevation is abutted by the adjoining building. The east elevation was not viewed, being fully abutted by a full-height gabled return. A modern four-panelled timber door opens to the south elevation. The south gable has a 1/1 window to the right at attic level. At the centre of the ground floor is a large tripartite window with the middle section boarded, with a plain timber fascia over.

The building is set back from the road with a tarmacadamed public parking area to the front. It is prominently sited at the south end of the terrace, facing an important junction on the approach to Portstewart town centre. A large two-and-a-half-storey modern extension with large dormers extends to the full length of the terrace at the rear. Agherton Parish Church is located to the north side of The Diamond.

The site shows buildings on the first edition Ordnance Survey map of 1830, but valuation records describe four low-value structures, possibly single-storey vernacular buildings valued between £1 and £2 10 shillings. The terrace was remodelled in its present form as seven dwelling houses between 1875 and 1882, reflecting Portstewart's growth as a bathing resort. The row shows little architectural pretension and likely retained fabric from its earlier predecessors. The building was newly remodelled and entered valuation records in 1882, leased from William Martin, who appears to have been the developer. At £5 10 shillings in valuation, number 15 was slightly larger than its neighbours. The initial tenant was Robert Blair, who moved to the neighbouring house in 1885. By 1900 the tenant was Margaret Jane McKeown, followed by Alexander Macauley in 1901 (recorded as an unemployed clerk living with his Edinburgh wife and 12-year-old niece), James Black in 1906, Isabella Potter in 1907, James McPeake in 1916, and William John McPeake who was resident in the 1930s. Valuer's notes of this period record that the house contained a kitchen, reception room and six bedrooms with rent at £1 3 shillings per month. The valuation plan shows the terrace with a communal rear yard containing a row of brick and corrugated iron WCs, one allocated to each dwelling house from number 9 to number 15, and a further row of coal sheds beside them.

The house was listed in 1977 when it remained a dwelling house. Shop fronts have since been inserted to the front and side, representing alterations that detract from the original building. Despite these inappropriate later alterations, the terrace remains an important example of late-nineteenth-century domestic architecture in Portstewart.