Riverdale Mill Complex, 24 Aghalee Road, Aghagallion BT57 0AR

Riverdale Mill Complex is a threshing mill complex dating from around 1870–72, located on the western side of Aghalee Road approximately 0.3 kilometres north of Aghagallon, close to the south-western shores of Lough Neagh. The complex has been restored, and in parts rebuilt, and converted to a wedding venue trading as 'Riverdale Barn', with the conversion work carried out from the late 1980s through to around 2000. All of the structures within the complex were restored around 2000 or later, and much of their detailing and layout dates from this period. The complex is of vernacular character and of industrial archaeological interest, though it does not retain sufficient historic fabric to meet the legislative test for listing. The threshing machine itself is missing, and its fate is unknown.

The mill is first recorded in a Valuation revision book entry of 1872, alongside a house and offices, all belonging to James Gilbert, with a combined rateable valuation of £15 10s 0d. No outbuildings appear on the first edition Ordnance Survey six-inch map of 1832, and though several small structures are shown nearby on the 1858 edition, their dimensions do not correspond to any of the buildings now present on the site. Later maps confirm that the mill was powered by water drawn from an adjacent pond fed by the Goudy River. It would have been used to mechanically separate and winnow grain from straw. The Valuation revision books record an increase in the property's valuation to £20 in 1878, falling back to £14 the following year, suggesting some construction work took place, though the nature of this is unspecified. From 1887 onwards, Jonathan Gilbert is listed in place of James as owner. The 1900 Ordnance Survey 25-inch map shows the threshing mill and pond among a number of buildings on the site. A detailed description survives in a 1912 Valuation notebook, which identifies sixteen buildings then extant, constructed variously in rubble masonry, brick, corrugated iron, or open-sided, with roofs of slate and corrugated iron. The surveyor described them as "all farm buildings in first class repair and fully utilized." The threshing mill itself was noted as rated at four horsepower and "only used for a short period each winter by Mr Gilbert for his own use." The 1920 Ordnance Survey 25-inch map is substantially identical to the 1900 edition, with only a few minor additions. Valuation notebooks from 1924 to 1934 record the mill's continuing operation by Jonathan Gilbert; valuations from 1934 onwards make no specific mention of the mill, likely because it was included within the general rating of the outbuildings. The mill appears to have remained in use into at least the mid-20th century, with someone employed on the premises until at least 1954. The Gilbert family are believed to have retained the whole site until around 1925, when the house to the north, known as 'Laganville' (now 26 Aghalee Road), was sold to James Mulholland. Around this time both houses to the north of the mill (now numbered 24 and 26 Aghalee Road) were damaged by fire and subsequently remodelled. The Gilberts continued to occupy 'Riverdale', the large formal dwelling built opposite at what is now 19 Aghalee Road and dating from 1911–12, until at least 1954, with a mill employee occupying the much-reduced number 24 until the same date. In the late 1980s the farmyard complex, by then disused, was purchased by its present owner, and over the following decade the buildings were converted into a wedding venue. This work included re-watering the dried-up mill pond, lining it with concrete, and refurbishing the waterwheel.

The site retains a legible historic setting on its south-western side, where the mill pond survives. Access from Aghalee Road is via a short drive leading to a vehicle gateway set within a tall rubble wall, which abuts Building 1 to the south and connects to a further gateway immediately south of the southernmost house (24 Aghalee Road) to the north. The gateway has square piers in polychrome brick with what appear to be original wrought-iron gates. To the north of the complex, and originally associated with the mill, are two houses of pre-1832 origin, both remodelled around the 1920s following the fire. On the opposite side of Aghalee Road stands the more formal mill-owner's dwelling of 1911–12, set within a garden containing ornamental rocaille structures dating from approximately 1880 to 1910.

The complex comprises four principal buildings arranged around a yard, with a more recent link structure connecting two of them.

Building 1 is the main mill building, positioned at the southern end of the site with its long axis running roughly east–west, backing on to the mill pond. It is a long, double-height and part two-storey range with a slate roof, constructed partly in rubble and partly in brick, with gabled ends. The building appears to have been constructed in two phases: the westernmost third, which housed the machinery and may in part be older, is largely in brick and has two levels, while the remainder is in a more unified combination of brick and rubble and contains a single double-height space. The north elevation of this eastern section features a series of tall semi-circular headed arches, now adapted as windows; a modern link to Building 4 largely covers the westernmost arch. The piers between the arches are in a markedly different shade of brick, which may reflect reconstruction. The east gable directly overlooks the mill pond and is rubble-built, rising from a rougher rubble base, with a series of small, regularly spaced circular ventilation holes dressed in brick and now glazed. The south elevation, also facing the pond, is similar to the east gable but additionally has two relatively large arched doorways dressed in brick: the left-hand door, which has a slated hood over it, opens on to a walkway built on top of a former sluice gate leading to a narrow stepping-stone causeway crossing the pond, while the right-hand door opens on to a recently constructed decked platform.

The westernmost third of Building 1 is mainly rubble to ground floor level and brick above, with a wholly brick lean-to at the west end. The north elevation of this section, partially covered by the modern link, has two brick-dressed windows and a doorway at ground floor level, with three further openings at first floor level, all with timber frames, and a timber door. On the south elevation, the original waterwheel is housed in a lean-to-like open-fronted projection in polychrome brick and rubble with a slated roof, with the opening for the millrace on the eastern face. This is a breastshot waterwheel with six arms and thirty or thirty-six buckets (the precise number was not discernible during survey). The hub and rims are of cast iron; the arms, buckets, and sole plate are of timber. The waterwheel has been restored and is original, representing the principal item of technical interest within the complex. The waterwheel gearing, or at least a portion of it, remains in place. To either side of the wheel housing is a window matching those on the north elevation, with a further two windows to the upper floor. The south face of the lean-to at the west end has a slightly larger window with a square ventilation opening immediately to its right, and this face is set at a slight angle to the rest of the building. A doorway and window are present on the western face, and above these, on the gable of the main mill building, there is a further window. To the north, the lean-to abuts another lean-to built against Building 2.

Building 2 is a two-storey rubble and brick gabled block attached to the west end of Building 1 via the lean-to, and resembling a small dwelling house in character. Its north elevation is in brick and features an unusual ground floor arrangement of two broad elliptical arched recesses with a smaller recess centrally between them. The left-hand recess contains a central doorway; the right-hand recess has a high-level window; and the central recess contains a small stone drinking trough. The piers separating these features and the outer edges of the larger recesses are all in yellow brick. At first floor level there are two windows matching those in Building 1. The south elevation is in rubble at ground floor level and brick above, with two large windows at ground floor level each having a slated awning-like hood, and two matching windows at first floor level. The west gable is in rubble and is featureless. The east gable is also in rubble but is largely covered by the lean-to, which is itself in rubble and has a large window with a doorway to its right, and a further window on the short north face.

To the north of Building 2 is a small yard enclosed to the west by a tall rubble wall. Building 3 closes the northern end of this yard and is a single-storey gable-ended block, largely in rubble with brick dressings and a slate roof. The south elevation has a large central section in what appears to be render made to resemble whitewashed rubble, presumably indicating that this portion was originally open or contained a large vehicle access opening. This section has two closely positioned doorways with a squat high-level window to the left of them. The west gable has a centrally positioned roundel dressed in brick. The north-facing rear elevation has four recently inserted high-level windows matching that to the south.

Building 4 is a large former barn forming the eastern side of the yard, with a long double-height form and walls of part rubble, part timber, and part corrugated-metal sheeting under a curved roof covered in similar sheeting. The south frontage and north rear elevation have been reconstructed in timber in recent years and are of little architectural interest; the south side was originally completely open. The east gable is largely clad in corrugated metal, while the west gable is mainly rubble with the uppermost third in corrugated metal sheeting. At high level on the south-east elevation there is an enamel maker's plate reading 'Smith & Pearson Ltd Dublin'. Smith & Pearson's Newcomen Foundry in Dublin exported metalwork and agricultural buildings worldwide from 1901 until the 1970s.

Connecting Building 4 to the main mill is a relatively recent single-storey flat-roofed structure in timber and glazed construction, extending roughly from the mid-point of the southern side of Building 4.

All of the structures have been converted to serve as parts of the wedding venue, accommodating function rooms, a bar, kitchen, storerooms, and toilet facilities. Roof trusses in the barns, doors, and floors all appear to be replacements in keeping with the originals, or in the case of tiled and timber flooring, entirely new introductions. The toilet block was not accessible during survey but is presumed to have undergone the most radical alterations within the complex.

External materials throughout the complex are as follows. Walls are in coursed rubble stone with sand and cement pointing, brick, and corrugated iron sheeting. Roofs are in natural slate and corrugated iron sheeting. Windows are in timber and aluminium. Doors are in timber and aluminium. Rainwater goods are half-round cast-iron guttering and downpipes.