Acorn Bank Mill with associated weir

Acorn Bank Mill with associated weir

A corn watermill of late 18th or early 19th century date, with later alterations and substantial reconstruction from 1989 onwards.

The mill is constructed of squared local Permian sandstone, mainly laid in courses, with later sections using snecked stonework and quoined gables. The roofs are covered with Westmoreland slate laid to diminishing courses with stone ridges.

The building forms a two-storey linear range arranged around the central mill. To the east, upslope, is a kiln and granary block, and to the west is a cart shed and saw mill. The granary is accessed at first floor level through its gable end, connecting through to the kiln's drying floor and then to the mill's first floor and store above the cart shed. The mill is powered by a waterwheel housed in a wheelpit on the north side, fed by a headrace running approximately 350 metres from an east-south-easterly weir. A yard on the south side provides ground floor access to various parts of the complex, with a passage for stoking the kiln running through the range.

Internally, the mill contains a staircase rising via a mezzanine floor formed by the hurst frame supporting the millstones. The main structural timbers are post-1989 reconstructions, but historic timbers survive in parts of the hurst frame, including a substantial bressummer beam formed from three scarf-jointed timbers that retains notches and mortises relating to earlier machinery arrangements. Additional bearing boxes built into the walls mark former machinery positions. A date stone inscribed 1823 is set into the lower part of the west wall. The first floor retains remains of a fireplace that was cut through to form a doorway to the store above the cart shed.

Externally, the mill presents three bays with a continuous roof line to the single-bay cart shed. The kiln and granary comprises four bays with a slightly higher roof, marked externally by two simple ridge vents. Plain verges run along the roof edges. All window and door joinery is traditionally detailed but represents restoration work from 1989 onwards.

The south elevation shows a scar line on the granary marking a former building extending to a bank barn to the south. The ground floor store doorway is quoined, while the adjacent kiln doorway has well-dressed monolithic jambs and appears to be a later insertion. The mill doorway also has monolithic jambs but appears reduced from a former quoined opening, now partly preserved with a window. Additional windows with monolithic jambs, lintels and sills light the first and ground floors. The cart shed entrance is segmentally arched.

The north elevation shows a quoined doorway to the kiln passage and a window with monolithic jambs to the first floor. Windows to the granary, store below, and store above the cart shed are unframed. Two openings between the mill and wheelhouse are shuttered, one with a quoined surround and the other timber-framed. The rear cart shed doorway has a timber lintel and appears to have been reduced in size.

The wheelhouse extends the length of the mill and is open to the west, with a lean-to roof extending from below the mill roof. It is constructed of snecked stonework to eaves level, with the east end timber-boarded above. The timber launder approaches from the east on rubble stone piers. The wheelhouse north wall contains a wall box and sleeved iron bar, both interpreted as relating to reuse of a second waterwheel position for a gypsum mine in the 1920s.

The east gable is built into the rising ground with a single doorway to the first floor granary. The west gable has a centrally placed ground floor window with a bearing box set into the wall above it to the north.

The kiln was reconstructed in 2016 but incorporates some original stonework and ironwork, including perforated cast iron tiles that formed the drying floor.

The mill is powered by two waterwheels, both iron-rimmed timber-spoked centre-drive wheels approximately 3.66 metres in diameter and 1.1 metres wide, with timber buckets. The upstream wheel is a pitchback wheel driving two sets of millstones (including French burr stones) and ancillary drives via a spur wheel. The second wheel, of more complex design, originally incorporated a secondary rim drive and was operated as an overshot wheel, also driving two pairs of millstones and further ancillary drives, though less machinery survives for this wheel. The sack hoist and jigger are reconstructions. Most gearing is cast iron with significant timberwork, much of it restored, and restoration using traditional methods has been ongoing since the 1990s, as documented in a 2010 building survey.

Water supply comes from the Crowdundle Beck approximately 350 metres to the east-south-east, where a simple stone-built weir (excepting the sidewall and sluice) dates to the 19th century or earlier. The listing also includes a stone-lined wheelpit for a third waterwheel position, marked by a surviving bearing stone on its south side, which forms the tailrace discharging directly into the beck below the mill. The headrace, approximately 400 metres long and gently meandering, appears to follow courses shown on early maps but is predominantly an earthwork feature not thought to be stone-lined and consequently not included in the listing. Later 20th-century garden landscaping features including bridges, spillway, revetment wall and viewing platform are also excluded from the listing.