20 Waterside, Coleraine, Co. Londonderry, BT51 3DP

20 Waterside is a three-storey-with-basement, Georgian-style end-of-terrace building, constructed circa 1866–68 as the final phase of a wider terrace development that had largely been completed by around 1854. It forms part of a largely homogeneous terrace along the south side of Waterside, one of the main approaches into Coleraine town centre across the nearby Old Bridge. The building occupies a prominent corner site at the western end of the terrace, at its junction with Killowen Street, and was designed within a framework overseen by Samuel Angell, the Worshipful Company of Clothworkers' surveyor in Ulster, and surveyor Stewart Gordon.

The building is rectangular on plan with a canted north-west corner and multiple abutments to the rear. The roof is partially hipped slate, with blue-grey angled ridge-tiles and lead-covered hipped ridges; the brick chimney has been removed. Ogee cast-iron rainwater goods are mounted on an in-stepped smooth rendered eaves course, with roughly rendered cogged brickwork to the rear. External walls are painted roughcast render, left unpainted to the rear, with a smooth rendered projecting plinth and sill courses.

The principal elevation faces north and is two openings wide on the upper floors, with single windows to the canted north-west corner. Windows throughout are square-headed 1-over-1 timber sash, generally set within smooth plain rendered architraves with a keystone motif to the upper centre, and plain projecting sills. The first-floor windows on the principal elevation have a moulded sill course. The ground floor has a 20th-century timber shop front with three narrow window openings to the centre, fronted by painted cast-iron railings. There are replacement multi-panelled timber doors to each side — giving access to the shop on the right and to the accommodation above on the left — with transoms above blocked with plain timber.

The canted north-west corner retains a former main entrance, now blocked up. The east elevation is abutted by the adjoining terrace. The rear (south) elevation is largely obscured by a two-storey building to the south; limited inspection reveals a blank main elevation except for a metal-faced modern timber door to the right of the ground floor, with the remainder abutted by a two-storey gabled return. The south elevation has a blocked opening to the first floor right, exposed brick and rubblestone walling on the ground floor, and vestiges of beam inserts indicating that a previous roof or floor extended over the rear yard to the south. The right cheek is blank and abutted by a mono-pitched corrugated plastic and timber canopy. The left cheek has two windows on each floor, all blocked. The west elevation contains three vertically aligned windows to the right side, the lower two of which are blocked.

The enclosed rear yard is bounded by a two-storey flat-roofed outbuilding to the south, built in brick and rubblestone with partial roughcast render, and all elevations appear blank except the west, which contains a 6-over-6 timber sash window with rendered reveals over a large opening fitted with a modern metal roller blind. Single-storey walls of similar construction bound the yard to the east and west; the west yard wall has a metal-faced replacement timber door and window with reveals matching those of the west elevation of the main building, while the east yard wall has a timber-sheeted and braced door opening onto an alley. The left and right sides of the main building are abutted by single-storey brick and partially rendered walls, each pierced by a door opening, with a timber-sheeted door to the right side.

The building is set in an urban context, with its principal elevation directly fronting the main road into Coleraine town centre. A similar terrace stands on the opposite (north) side of the street, and the Old Courthouse is located a short distance to the west. The building sits on the western bank of the River Bann, to the west of the central Diamond.

The historical context of this building and its terrace is closely bound up with the Worshipful Company of Clothworkers, one of the London Merchant Companies responsible for developing and settling County Londonderry from the early 17th century. This area of Killowen Parish — now known as Waterside — was originally a suburb of Coleraine and fell within the Clothworkers' proportion. Over the following two centuries the Company leased out these lands, often to absentee landlords, leading to general decline and little new construction due to uncertainty of tenure. The Company regained direct control in 1840 when the lease expired, and a substantial programme of improvement followed, covering buildings, infrastructure, and education.

As part of this improvement, a new bridge of increased height was built around 1844 to replace a previous timber structure of around 1735, with stabilising works carried out to the western river embankment. The raising of the street level on the Killowen side to match the new bridge height affected the existing buildings, and it was decided to demolish and rebuild the entire Waterside area to create a more dignified approach to the Company's estate from the main part of Coleraine. The general street layout had already been established, so the terrace did not change greatly on plan; however, the design, scale, and style of the new buildings were subject to strict architectural discipline. This was set by the neighbouring Clothworkers' Arms Hotel, erected around 1846, which marked the first stage of the redevelopment and prompted the demolition of neighbouring houses from 1847. According to James Curl (1986), the houses on the southern terrace were erected first to provide visual balance to the then-isolated hotel opposite. Angell designed a suitable corner terrace to complement the hotel and to line the processional approach into the estate via the new bridge. Although designs for the remaining buildings were largely produced by other architects, each was strictly regulated by Angell and Gordon to conform to the overall scheme. The plain, balanced, and unembellished style of the terrace reflects the Clothworkers' Company's conscious decision to avoid the excessive ornamentation embraced by other London Companies during this period of widespread architectural improvement. By around 1854 the terrace was largely complete, with the Clothworkers' Company having spent approximately £4,000 on erecting houses in the Waterside area during this period. The present building at No. 20, along with the immediately adjoining building to the east, was completed later — around 1866–68 — as confirmed by its addition to valuation records in 1868.

Griffith's Valuation of 1856 records a previous house and outbuildings on the site, valued at £12 and described as "very old," indicating an earlier structure predating the current building. The current property was first occupied under the ownership of John Ross by Peter Martin in 1869, when it was valued at £21. Ownership passed to Daniel Christie around 1893, and by 1898 the value had decreased to £18 following periods of vacancy. The value rose again in 1910 after a shop was added to the premises. The building outline has changed little since the Town Plan map of 1882, though field evidence shows that abutting outbuildings to the rear have been modified and partially removed in recent decades.

No. 20 is an important element in the overall redevelopment of Waterside and has group value with the other listed buildings in the terrace. It also holds significance as a representative example of the typical urban form of living accommodation over a shop, characteristic of the period and of this part of Coleraine.