Steam Engine House, Mill Number Three, New Lanark

The Steam Engine House at Mill Number Three in New Lanark was built in 1816, with the engine house added in 1881. This three-storey building, which has four storeys at the rear, features a ten-bay design with a piend roof. It was originally an Institution for the Formation of Character and includes a prominent, pediment-gabled three-bay central section along with an advanced two-bay engine house with arched windows on the north side. The structure is constructed from squared rubble with droved and stugged ashlar dressings and has tabbed quoin strips. The front and rear of the Institute display regular fenestration with slightly raised tabbed margins and projecting cills, while the former engine house features large, tabbed, round-arched windows.

Notable features include a central Doric portico at the ground floor of the Institution, supported by coupled columns, and a two-leaf timber-boarded door. An oculus is present at the apex of the pediment. The Engine House has stone steps leading to a central two-leaf timber panelled door set in a round-arched architrave with a fanlight above. A ramped late 20th-century bridge connects to the former loft door on the south side at the upper level, linking with Mill No 3.

The Institution has 16-pane glazing (with 8-pane windows on the upper storey) in timber sash and case windows, while the Engine House features small-pane glazing in fixed timber windows. The south elevation of the Institution has a wallhead stack with an ashlar cope. The roof is covered with graded grey slates, and cast-iron rainwater goods with hoppers are present.

Inside, the Institution originally had a symmetrical plan on the ground floor, with a larger room on the right occupying two-thirds of the area and a smaller room on the left. The basement retains its original cobbled floor and features cast-iron columns. The top floor includes a hall with a gallery running along three walls, supported by cast-iron columns. The interior of the Engine House was originally plastered but is now exposed stone, with a timber-lined ceiling supported on wrought iron box girders.