Belfast Roof Truss Buildings at Hilden Mill, (off Mill Street), Hilden, Lisburn, Co. Antrim, BT27 4RR

These eight buildings form part of the Barbour Threads Mill complex at Hilden, near Lisburn, and are recorded as a group on account of their Belfast Truss roofs. The wider mill complex is recorded separately. None of the eight buildings has been judged to meet the criteria for statutory listing, though several are of some industrial archaeological interest.

Belfast Truss roofs were a common feature of industrial, commercial and agricultural buildings across Ulster and beyond in the late 19th and early 20th centuries. Because of how they were built, many have since been replaced with more durable roofs or lost altogether through demolition. Their increasing scarcity makes surviving examples a valuable part of local civil engineering heritage.

The Barbour Threads Mill complex as a whole is a large, sprawling, mainly brick-built site on the eastern edge of the village of Hilden, straddling a bend in the River Lagan. Most of the buildings lie to the west of the river, but the eastern portion of the site occupies a narrow strip of land — effectively a river island — between the Lagan itself and the Lagan Navigation canal, which branches off and runs parallel to the river. The mill was established in 1823, but the complex as it survives today dates largely from around 1850 to around 1910. Although some parts of the site were formally planned, much of the complex grew organically in response to commercial opportunities in the mid to late 19th century, in the manner typical of many Ulster mills of the period. Administrative and ancillary buildings are broadly concentrated on the western side of the site; manufacturing, storage and related functions occupied the eastern side and the river island. Some of the Belfast Truss-roofed structures are likely to have been built in the 1880s, when the valuation records document significant construction activity. All of the sites of Buildings 1 to 5 are shown as developed on the Ordnance Survey maps of 1903 and 1904, and the presence of Belfast Truss roofs on these buildings is confirmed by a detailed survey recorded in a valuers' office notebook from 1916. Building 7 is also recorded in that survey. Building 6, an open canopy close to the southern edge of the complex, does not appear on any map up to and including the Ordnance Survey map of 1932, though it appears to be earlier than that date.

Building 1 is a former two-storey administration block near the main vehicular entrance on the northern side of the site, shown on the 1903 Ordnance Survey map. A bay to the eastern side and a southern addition have both been removed, leaving an almost rectangular footprint. On the north facade, a shallow two-storey flat-roofed bay projects to the east, with a single-storey lean-to entrance porch to its west. Walls are mainly plain red clay facing brick; the projecting bay is finished with polychrome brick banding. The east gable wall has been rebuilt in modern metal cladding. Part of the west wall incorporates stone panels, suggesting this building may originally have been an extension to an earlier structure. Window openings are segmental-headed; some original timber sash frames survive alongside various replacement frames. The fenestration is regular with evenly spaced openings. Eaves and verges have painted timber fascias and the roof covering is felt. The building has been modernised internally to provide offices. Although it does not have a Belfast Truss roof throughout, and is an amalgamation of buildings of different dates and styles, it was considered that the building as a whole does not possess sufficient special historic merit to warrant listing.

Building 2 is another former two-storey administration block near the main vehicular entrance on the northern side of the site, also first shown on the 1903 Ordnance Survey map. It is likewise an amalgamation of buildings of different dates and styles. A later two-storey flat-roofed addition is attached to the west side, and a single-storey lean-to roofed section to the east. The original central section is covered with a barrel-vaulted Belfast Truss roof. Walls to this section are of random rubble construction. Window openings are of various types with flat and segmental heads; frames are mainly timber sash. Fenestration is mainly regular with evenly spaced openings. Eaves and fascias are painted timber. The decorative canopy on the north elevation is separately listed. The building was considered interesting but not of sufficient merit to warrant further listing protection beyond that already afforded to the canopy.

Building 3 is a long two-storey block, first shown on the 1904 Ordnance Survey map, situated on the river island and fronting onto both the river and the canal. The roof is predominantly a double-pile pitched roof, but a section of Belfast Truss roof covers the southern part of the building, which also has a small single-storey felt-covered extension on the south gable. Walls are mainly plain red clay brick. Window openings are segmental-headed with mainly sash frames. Eaves are timber. The building is in very poor condition throughout, and although it has some historic interest it was considered not to meet the criteria for listing.

Building 4 is a typically plain four-storey mill building with a projecting stair tower and segmental-headed window openings. It sits at the north-eastern side of the site overlooking a large weir in the river and first appears on the 1903 map. It is an addition to one of the large four-storey mill ranges forming the main conglomeration at the northern end of the site. The building is mostly constructed in plain red clay brick, with the north elevation in rendered basalt rubble. Its gable — part brick, part rendered basalt rubble — shows where it originally abutted a three-storey building that has since been demolished. The building has a Belfast Truss roof but is generally in poor condition. It was considered that it does not possess sufficient historic merit to extend existing listing protection to include it.

Building 5 is located on the southern side of the site, fronting the river, and is roughly rectangular in plan. The building is part single-, part two-, and part three-storey and may have been constructed in stages, though it appears in its entirety on the 1903 Ordnance Survey map. The single-storey section is divided equally into three parts, the last of which has collapsed. The building has a Belfast Truss roof, which has partly collapsed. Walls are mainly plain red clay brick. Window openings are segmental-headed; some have been bricked up. Frames are timber, mainly multi-paned fixed lights. Gables rise to parapets and eaves are formed in timber. The building's condition was considered too poor to merit listing.

Building 6 is an open porch structure attached to the eastern end of a two-storey building near the southern end of the site. At the time of survey the entire area was filled with metal trolleys, making close inspection impossible; only long-range views of the trusses could be obtained. As far as could be determined, the trusses have right-angle bracing, suggesting they are of McTear style. The porch does not appear on any pre-1932 Ordnance Survey map, though it appears to be earlier than that date. The structure was in poor condition and, being attached to a non-listed building, was considered not to meet the criteria for listing.

Building 7 is a small single-storey detached timber building at the southernmost part of the site, sitting at the head of a small branch canal. A later single-storey metal-clad building with a pitched roof is attached to its southern gable. Walls are faced with vertical timber boarding. Fascias and bargeboards are timber. Window openings are flat-headed and have been boarded over. Although of some interest as a piece of 20th-century industrial heritage, the building was not considered to be of special historic or architectural significance.

Building 8 is a two-storey building on the south side of the site, adjacent to the west bank of the river. A two-storey flat-roofed building is attached to its west side and Building 5 abuts its south gable. The building is brick-faced with segmental-headed openings and multi-paned timber window frames. It has a Belfast Truss roof. An 1889 illustration of the mill confirms that this building was already standing by that date. Although of interest, its poor condition and its position abutting other non-listed structures meant it was considered unsuitable for listing protection.

The mill complex has a lengthy history. It was founded in 1823 by William Barbour (1795–1875) on the site of a bleach green originally established by Samuel De La Cherois, one of the Huguenot settlers responsible for developing the linen industry in the hinterland of Lisburn in the early 18th century. William was the son of John Barbour Senior (1755–1823), who had moved from Paisley to Lisburn around 1784 and established a thread manufactory at The Plantation in Ballymullan townland, almost two kilometres south of the Hilden site. On the death of their father, The Plantation works passed to William and his elder brother John. According to the historian Kathleen Rankin, while William had ambitions to twist thread using power-driven machinery, his brother John Junior preferred to continue with the more conservative methods already in use. This prompted William to establish his own enterprise. Following the untimely death of his brother in 1831, William purchased the goodwill and assets of the original concern and transferred all operations to the new factory at Hilden, where he had also built himself a new house, Hilden House, described as a very commodious square building.

The house and some mill structures appear on the Ordnance Survey map of 1832 to 1833. By April 1835 the site already included a thread mill measuring 71 by 25 by 22 feet, a barn and store of 27 by 19 by 13 feet, drying houses, a boiling house, a dipping shed, and various other sheds. The Ordnance Survey Memoirs of late 1837 describe the Hilden works as the most extensive thread factory in Ireland, noting a three-storey stove house and water mill, two-storey offices and yarn stores, and all other buildings as single-storey and slated throughout. The breast wheel measured 15½ feet and drove 20 thread mills, each with 48 spindles for twisting thread, along with a double beetling engine and sets of rollers. The works produced between 200,000 and 300,000 hanks of yarn annually and employed 300 people of both sexes.

Between 1837 and the revised Ordnance Survey map of 1858, the site was transformed, expanding significantly in the area between the early buildings and the River Lagan. A long row of mill workers' dwellings along the south side of what is now Bridge Street formed the nucleus of the village of Hilden. By the early 1860s much of the large multi-storey conglomeration at the northern end of the site was either in place or taking its present form. The massive five-and-a-half-storey main mill block, with its distinctive rounded stair projection, was standing by this time, though without its westernmost all-brick quarter. The rubble section of this block bears a date stone of 1851, with brick additions dating from the later 1850s or early 1860s. The rateable value of the mill buildings was £900 in 1862, rising to £1,160 by 1867 and to £1,390 by 1880, reflecting both new construction and the prosperity of the business. Much of this expansion was driven by the boom in linen sales caused by the cotton shortages of the American Civil War years.

Significant further building activity took place during the 1880s, including a four-storey flax store, a single-storey tow store, additions to the dye house, a bobbin store, and later the raising of the flax store by two storeys. By 1888, according to Bassett's County Antrim directory, the firm of William Barbour and Sons was ranked as the largest manufacturer in the world of tailors' thread and shoemakers' thread for hand and machine sewing. A description published in 1889 records the works as covering 34 acres with 30,000 spindles spinning thread and 8,000 twisting it, driven by engines of 2,000 horsepower consuming 200 tons of coal each week, with approximately 5,000 people employed at Hilden and at two other sites in Sprucefield and Dunmurry, along with 1,200 at a branch of the firm established at Paterson, New Jersey by William Barbour's second son Thomas.

In 1890 to 1891 the western end of the main mill block was completed, with a large metal water tank, a two-storey engine house, and a boiler house added to the south. In 1898, William Barbour's eldest son John Doherty Barbour (1824–1901) brought together the Barbour businesses in Ireland and the United States, along with a Scottish company, Finlayson Bousfield and Company of St Johnstone, to form the Linen Thread Company. Five further companies subsequently joined, including Dunbar McMaster of Gilford and Greenwich New York, F W Hayes and Company Limited of Banbridge, and Crawford Brothers of Beith in Ayrshire. This commercial consolidation was reflected in further physical expansion, and by the time of the Ordnance Survey maps of 1903 and 1904 the site had reached much of its present extent. A coloured illustration dating from shortly after 1916 shows the works at what was arguably their zenith.

Thread production continued throughout the 20th century despite a gradual fall in demand after 1945. In 1978 the company was sold to the London-based Hanson Trust and amalgamated with the Campbell Mill at Mossley, Newtownabbey, to form Barbour Campbell Threads Limited. Thread production continued at Hilden, but reduced orders — driven mainly by cheaper overseas competition — led to a steady decline in output and the eventual closure of the mill in 2006. At the time of survey the site was undergoing development.