18 Lower Castle Street, Glenarm, Ballymena, Co Antrim, BT44 0AT

18 Lower Castle Street is a plain, two-storey rendered terraced house dating from around the 1840s, forming one of a short block of three largely identical properties on the east side of Lower Castle Street, a short lane branching southwards from Castle Street itself. A two-storey flat-roofed return has been added to the rear in relatively recent times, probably around the 1980s. The house has been reconstructed and altered, though some internal detail survives.

The front elevation faces roughly west and is asymmetrical. To the left on the ground floor is a timber sheeted door with a five-pane rectangular fanlight. To the right of this is a sash window with Georgian panes in a 6/6 arrangement, and there are two similar sash windows on the first floor. The front façade is finished in painted roughcast.

At ground-floor level on the north gable, there appears originally to have been a large lean-to belonging to the property immediately to the north, No. 16 Castle Street. The west side of this former structure survives flush with the front elevation of No. 18, but only a small shed now remains against the gable itself. At attic level on the north gable there is a small two-pane window. The gable is finished in roughcast, partly painted.

To the right side of the rear elevation is the large two-storey flat-roofed return of probable 1980s construction. On its south face there is a door and a modern window at ground-floor level, with a similar window to the first floor. The rear façade of the main body of the house has an enlarged window with a modern frame at ground-floor level and another on the first floor. The rear elevation is finished in dry dash. The roof is gabled and slated, with a rendered chimney stack to the south. Rainwater goods are a mixture of cast iron and PVC.

Castle Street is the shortest of Glenarm's four principal original streets, running westward from the intersection of Toberwine and Altmore Streets to the bridge over the Glenarm River, with Lower Castle Street branching off southwards near the western end. The street formed part of the main road from Larne, a route of possible medieval origin that wound northwestwards through The Vennel to Castle Street and over the river bridge before curving north toward what is now the Straidkilly Road. The earliest leases within the Antrim Papers relating to plots and buildings along the street date from 1711, though at least one building — the old parish church — was already standing at the southwest end of the street as early as 1683. The old 13th-century Bisset castle, probably a tower-house type structure, is reputed to have stood at the northeast end of the street, and the still-extant former courthouse, believed to have been standing at least since the 1750s, is thought to incorporate part of its ruins. The bridge at the west end of the street was erected in 1682 — prior to this, travellers forded the river — but had to be largely rebuilt in 1713 following flood damage. For obvious reasons the street was originally known as Bridge Street, a name that appears to have persisted until the mid-19th century.

On John O'Hara's map of 1779, the earliest surviving plan of Glenarm, the street is shown fully developed on both sides, with rows of properties to the same extent as shown on the Ordnance Survey map of 1832. Given the evidence of the 1859 valuation, most of the buildings indicated in 1832 are likely those standing today, with the short terrace on Lower Castle Street appearing around 1835 to 1840. O'Hara's map clearly shows Castle Street's pre-eminence as part of the main northward route from Larne, with the road skirting the grounds of Glenarm Castle on the west side of the river. In the early 19th century this arrangement was radically altered: the old road was superseded by the new Coast Road and the new Glenarm Bridge, built in 1813, at the north end of the village, and the grounds around the castle were enclosed. This process, complete by the mid-1820s, appears to have led to a gradual diminution of the street's status. It is perhaps telling that while a notable such as Lord Antrim's agent could be found living in Castle Street in the late 18th century, by the mid-1830s the agent had moved to the south end of the newly widened, and considerably grander, Altmore Street.

The short terrace to which No. 18 belongs is recorded in the valuation of 1859 but does not appear on the Ordnance Survey map of 1832, and on the evidence of the valuation grading was probably built around 1835 to 1840. In 1859 the terrace was in the hands of a Mrs Eliza Boyd, with this particular property occupied by a Rachel Murphy and a Thomas Watson.