The Hafod Copper Works was built by John Vivian in 1808-9 on southern part of level land enclosed by a loop of the tidal River Tawe. The area occupied by the works was bounded on the west by the Swansea Canal and later, to the north, by the Morfa Copper Works. In 1910 a new mill and engine house was built to house a single-cylinder Musgrave Uniflow engine. this comprises a full height machine hall, some 2m above exterior ground level, and a basement beneath, a freestanding chimney on the southwest side at the west corner, and an extension to the southeast shielding the cable drive. To the south east of the building, a flywheel and a set of rollers are also in situ.

The machine hall is full height, open to the roof. The northeast half of the hall is occupied by the engine which is installed on a solid concrete base that continues through the basement. Over the basement voids, the floor is a concrete slab reinforced with steel girders, and is surfaced with terra cotta quarry tiles in walkway areas. In several places the basement is open; these areas would have been covered with removable wooden or sheet metal flooring. Along the long sides, between each window opening, pilasters support rails for an overhead lifting gantry which is in situ; a plate on the hoist cradle John Musgrave & Sons Ltd., Bolton. 1910. The window openings have wooden frames with six large panes, the top pair in some forming opening lights, while in the east corner is an external doorway. Timber king-post trusses support the roof. The basement comprises two large voids either side the central solid engine block.

The Uniflow engine was the last major development in reciprocating steam engine design, being an attempt to overcome the heat loss experienced through condensation of steam in the cylinders during the exhaust period by allowing the steam to move in one direction only. A license was obtained by John Musgrave & Sons, Globe Ironworks, Bolton in 1909 and manufacture of Uniflow engines by them commenced in 1910. This engine is therefore one the earliest Uniflow engines to be constructed, the type continuing to be made by Musgraves well into the 1920s.

The walls are of grey-black brick with two intermediate horizontal bands of terra cotta bricks and a third, dentilated, course just below the eaves. The north and west corners below the lowest band are rounded and have imitation quoins in red terra cotta bricks. The hipped roof is covered with slates. The chimney stands a little away from the engine house, connected to it below present ground level. Square in plan it stands to a height of 27 metres and tapers from the base to the top. The main body is constructed of orange-grey brindled brickwork but the top two metres are in red brick and may be a later extension. Seven horizontal iron-bar tie frames set at approximately 1.5 metre vertical intervals clasp the upper part of the chimney. At ground level, in the northwest face, is a small, camber-headed open archway set in a larger, round-headed blocking. Immediately to the northwest is an open, concrete-walled sump.

The Rolling Mill lies to the south east of the engine house. The flywheel is by Musgraves, the gearbox by Taylor & Farley of West Bromwich, the rollers by the Glanmor Foundry, Llanelly. The surviving machinery is situated to the southwest of the flywheel. There was most probably similar equipment to the northeast, driven directly from the flywheel, and more driven by a secondary drive
The former No.1 Rolling Mill Engine House is a good example of early 20th century upgrading of industrial plant, where the building and the machinery contained therein are designed as a single entity. This structure is particularly unusual because of the survival, not only of its engine, but also of a substantial part of the machinery for which it provided power. The engine is one the first Uniflow engines to be built and it is a particularly rare and important survival.

The Engine House forms a part of the Hafod Copperworks complex (NPRN 34089), which includes a tramway viaduct (NPRN 34891), 1860-2 engine house, (NPRN 33743), locomotive shed (NPRN 300188), and offices (NPRN300190).

RCAHMW 9th March 2009