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

A two-storey mid-terrace building, originally a house and now commercial premises, built around 1880 and located on the east side of the Diamond in Portstewart town centre. The building is the best preserved in the terrace, retaining its original composition and much of its architectural detailing, and forms an important component of the listed terrace group as a whole.

The building is square on plan with a pitched artificial slate roof, blue and black angled ridge tiles, and a cement-rendered chimneystack. Plastic rainwater goods are fitted to the projecting eaves. The walls are painted ruled-and-lined render. Windows throughout are 1/1 timber-framed sash windows with horns and projecting painted sills; those to the first floor are slightly diminished. The principal elevation faces west and is three openings wide at each floor. At ground floor to the left is a replacement six-panelled timber door, slightly recessed with a small step. The north elevation is abutted by the adjoining building (HB03/08/004E), and the south elevation by the adjoining building (HB03/08/004H). The east elevation was not viewed during assessment.

The building is set back from the road with a tarmacadamed public parking area to the front, situated at the south end of the terrace. The terrace is prominently located, facing an important junction on the approach to Portstewart town centre, in an area characterised mainly by commercial units housed in two-storey terraces on the southern edge of the town. A large two-and-a-half-storey modern extension with dormers extends along the north side of the terrace, running to its full length at the rear. To the north side of the Diamond stands Agherton Parish Church (HB03/08/001).

Buildings are shown on this site on the first edition Ordnance Survey map of 1830. However, valuation records of that period describe the dwellings then present as four structures of low value, ranging from £1 to £2 10s, and likely therefore single-storey vernacular buildings. The terrace was remodelled in its present form as seven dwelling houses between 1875 and 1882, reflecting Portstewart's growth into a successful bathing resort, though the row is without architectural pretension and likely retained fabric from its simpler predecessors. The larger house and shop at the northern end operated as a successful commercial enterprise, while the attached terrace was let out to working-class tenants. Number thirteen was entered into valuation records in 1882, newly remodelled and leased from William Martin, suggesting he was the site's developer. The house and its neighbour were both valued at £4 10s. The first tenant was James Dolan, followed by Robert Blair in 1885. By 1900 the tenant was Mary Blair, probably Robert's widow, who ran the premises as a lodging house while raising her five children, the eldest of whom worked as a labourer. Two boarders—a carpenter and a retired farmer—lodged at the ten-room house, which was designated second class. In the 1930s the house contained a kitchen and five bedrooms with a rent of £1 per month. Valuer's notes show a plan of the terrace indicating a communal yard containing a row of brick and corrugated iron WCs, one allocated to each dwelling house from number 9 to number 15, with a further row of coal sheds beside them. The house was listed in 1977. In 1990 renovations took place to the door, windows and gutters. In 2004 internal alterations were carried out and an extension added to the rear to provide a ground floor office and first floor residential accommodation.