Newtownabbey Borough Council offices, Mossley Mill, Newtownabbey, Belfast, Co Antrim, BT36 5QA

Mossley Mill is a large and impressive L-shaped four-storey local government office complex, now serving as the headquarters of Newtownabbey Borough Council. It combines two large former flax mill blocks dating from the mid to later 19th century with a contrasting late 1990s glazed entrance section, and occupies a site in Ballyhenry townland with an industrial history stretching back to at least the mid 18th century. The mill complex can still be read as a coherent entity, and its conversion to council offices carries added significance for a large part of the local population whose family members would have worked here.

The site sits to the east of Carnmoney Road. The large mill pond and tall chimney occupy higher ground immediately to the west of the building, with a landscaped drive and grounds to the north-north-west. To the immediate east, a large collection of buildings that originally formed roughly half of the late 19th century mill complex have been demolished, leaving only a long three-storey hipped-roof basalt building and an adjoining two-storey rendered and gabled structure at the south end of the site. A channelled stream runs along the north side of the complex and a railway line lies just beyond it. To the north is the main drive, with a recent gate screen and railings to the east side of Carnmoney Road North, and a large paved forecourt and car park to the west.

The two four-storey former mill blocks are set at right angles to each other and joined at their north-west corner by the large glazed late 1990s entrance section, giving the overall plan its L-shape. The entrance section is flat-roofed and completely glazed on its curved west side, with the north side in glass and a large full-height central brick section. It is prominent yet contrastingly more graceful and airy than the typically stark and angular mill blocks it connects.

The northern mill block is the longer of the two and was built some time prior to 1861, possibly around 1850, with its top storey added around 1879. From the later 1800s until recently it was abutted at both its east and west ends by other structures, which have since been cleared away. This block has not been renovated and is currently unused. It is built in semi-coursed basalt rubble with granite in-and-out quoins and in-and-out brick dressings to the windows. The windows are arranged in uniform rows on each floor of the long north and south elevations: those on the first three floors are flat-headed and those on the uppermost floor, which was added later, are segmental-headed. Window frames on the ground, first and second floors are timber with small panes, with metal-framed hopper openings at ground floor level. Those on the third floor appear to have wholly metal frames with margin panes. A few windows on the north and south elevations are now blocked. Between the second and third floors on the north elevation, the stone parapet or eaves course belonging to the original roof line is still in place; on the south elevation there is a deep cement-rendered band between these floors. At the east end the façade projects slightly on both the north and south elevations, within which was or is the stairwell. There are two narrow full-height brick projections on the north elevation, which housed the toilets. The short east elevation has a more dilapidated appearance because it was until recently completely covered by another structure. It has three evenly spaced openings on each floor, presumably originally mainly windows and possibly later used as doors, all of which are now boarded up; the outlines of the former structures abutting this elevation are still visible. The block has a flat roof with a stone parapet and cornice course. At the west end of the roof, spanning across to the late 1990s section, a large mainly brick-built flat-roofed single-storey addition has been made.

The western mill block is somewhat smaller and appears to have been built as a whole in 1879. It has the same stark, uniform character as the northern block, with a coursed basalt rubble façade, banks of brick-dressed windows and a flat roof, but this block has been completely renovated. Because of the higher ground level to the west, the ground floor of the west elevation is only visible up close. At this level there is a row of window-shaped recesses largely filled with basalt to match the façade, but with three on the left-hand side filled in brick. There is a larger light well on this side and these recesses may originally have been proper windows. On the upper floors are rows of segmental-headed window openings, all with new metal frames. The windows on the uppermost floor are slightly shorter than those below, and two of them have been lengthened to form balcony doorways. Between the second and third floors there is a deep rendered band which appears to have been added recently. At third-floor level there is a string course at window arch springing level, which appears to be of sandstone. The east elevation broadly repeats the appearance of the west elevation but is fully exposed on all floors, including at ground-floor level. On the ground floor to the right is a large vehicle doorway with a large painted lintel bearing the date 1879; this doorway appears to be no longer in use and is filled with large timber tongued-and-grooved sheets. At the far right-hand end of the elevation is a relatively narrow section set slightly back from the main face, which repeats the detailing of the rest of the block but has a large segmental-headed pedestrian doorway at ground level with in-and-out granite dressings, a recent timber double door and a large fanlight. Immediately to the right of this section is a recent full-height entirely glazed section which spans across to the northern block. The narrow north elevation has a window on the left on each floor and a brick-filled window-like recess to the right. The south elevation has a metal-sheeted flat-headed pedestrian doorway at ground floor, with a single flat-headed opening on each upper floor filled with what appears to be metal sheeting. The flat roof has a large recent brick-built services section at the north end.

To the south boundary of the site the long three-storey hipped-roof building survives. Built in basalt rubble with brick-dressed openings, it appears to date from some time after 1861. On the long north and south elevations there are uniform rows of relatively small flat-headed windows, mainly filled with mid to later 20th century frames, and several windows have been blocked. On the ground floor of the north elevation there is also a pedestrian doorway to the left and a large vehicle doorway to the right, both relatively recent insertions and somewhat awkward in character. The east elevation is blank. The west elevation has a window on the right on the second floor and a window-like recess to the left. This building is abutted on its west side by a long narrow and somewhat dilapidated two-storey rendered and gabled building of possible pre-1861 construction, recorded in that year as a fine flax store, though much of its façade was obscured from view. The three-storey building has a slated hipped roof with a tall brick chimney stack at the east end and another at the west. On the high ground immediately to the west of the main building stands a tall octagonal tapering brick chimney. There has been a chimney on this site since at least 1852, though the present one may be a later replacement.

The site has a long industrial history. According to the Ordnance Survey memoirs of 1839, an industrial complex of some kind has existed here in Ballyhenry townland since at least the mid 18th century. The earliest known establishment was a bleach works run, in its final years at least, by a Mr Thompson, which closed around 1760. It was replaced by a flax scutching mill and then a cotton factory run by Messrs Stenton and Graham. Around 1805 this was acquired by Edmund and Thomas Grimshaw, who around 1818 converted it to a cotton printing works. They were the sons of Nicholas Grimshaw, a Lancashire-born cotton printer who moved to Belfast around 1770, established a print works at Greencastle in or around 1776 and swiftly became a leading figure in the Irish cotton industry. After Nicholas's death in 1805 his sons continued and expanded the business, acquiring other mills in the Carnmoney area. By the 1830s the decline of cotton manufacture in Ireland and the emergence of somewhat militant combinations among the printers led Edmund Grimshaw to convert the Ballyhenry works — by then named Mossley, in deference to the Grimshaws' Lancashire connections — to a flax spinning factory in 1834. In doing so Edmund rebuilt or refurbished much of the complex and created the large mill pond, which by 1840 fed a large metal wheel of 60 feet in diameter. It is difficult to gauge the full extent of the complex at this stage, since the first accurate map of the area was produced in 1832, a few years before Edmund Grimshaw commenced rebuilding. Little on that map corresponds to the site as it emerged later in the century, though there does appear to have been a structure on the site of the present three-storey hipped-roof building to the south boundary.

In 1859 the Mossley mill was bought by Henry Campbell and his second cousin John Campbell, with Henry supplying the capital and John managing the business. By this point the complex had taken on much of the form it would retain for the next 150 or so years, with the large spinning mill on the north side (at that stage three storeys), two-storey and single-storey office buildings and a manager's house to the north-west, and a scattering of buildings to the south including, according to the 1861 valuation, the old mill referred to above, at that point used as a rough flax store. This may be the building visible today, though the valuers describe it as two storeys, suggesting it was either later replaced altogether or raised a storey; the regularity of the present building indicates it is a replacement. At this date the mill had 7,060 spindles and was powered by two new 40-horsepower engines by Hickson of Bolton working together, each described as beautifully finished and fitted at a cost of over £2,000 each, said to be without the boilers.

The next major change to the complex came in 1879, when a large collection of buildings to the west-south-west — including a two-storey brick drying house and drying loft, a gas house and pumping shed, the old engine house, bundling rooms and coal stores — were demolished and the present four-storey western block was erected. The fourth storey may have been added to the northern block at the same time, as its detailing matches that of the southern block, though this is not certain. Further smaller buildings appear to have been built to the east of the southern block around this date, and with these additions the Campbells were able to add thread-making to the business. Alongside the expansion of the mill went the expansion of the Mossley mill village, with new workers' houses built at Old Row and Sunnyside to the north of the mill and a school established in 1868. Henry Campbell died in 1894 — his money was left in trust for the founding of a school or hospital, and Campbell College opened in Belfast that same year — and John died in 1901, but the Campbell family continued to run the business, expanding throughout the century and introducing the manufacture of synthetic threads in the 1960s and 1970s. Though there were inevitable changes to the buildings over time, the basic form of the complex remained broadly as established in the early years of the century.

In 1978 the company was sold to the London-based Hanson Trust, amalgamated with Barbour Threads of Hilden, and renamed Barbour Campbell Threads Ltd. Thread production was moved to Hilden, with spinning remaining at Mossley. In 1993 Mossley was bought by Herdmans flax spinners of Sion Mills and finally closed in 1995. In 1996 the site was acquired by Newtownabbey Borough Council, and the large south-western block was converted and extended into the new Council Civic Centre. The largest block on the north side was retained but remains untouched, as were the old store to the south end, the large chimney and the mill pond. However, the mass of buildings to the south and east, as well as those to the north-west — roughly half or more of the complex in terms of area — were cleared away.

The listing covers the original mill buildings: the large four-storey mill blocks, the three-storey store block to the south, and the chimney.