Former Mast House and Mould Loft

The Former Mast House and Mould Loft, now a museum, was built between 1753 and 1755 and altered in 1833. It features a weather-boarded timber frame and a slate roof. The building has a rectangular open plan with the mould loft occupying the three middle bays. It is a single-storey structure, with a second storey in the middle three sections and an attic above. The exterior displays a near-symmetrical arrangement of five gables, with the central gable being taller and having a raking roof that extends to the flanking bays above the mould loft. The ground floor has continuous garage doors and wide windows above, which include seven first-floor six-over-nine pane sash windows and five attic nine-pane windows in the middle range, while the flanking ranges have two first-floor six-over-six pane sash windows. The middle range also features large flat-headed dormers, three small ridge louvres, and flat roof lights in the other ranges, with the end ones having four dormers.

Inside, there is an extensive open space, with the mould loft supported by large posts featuring diagonal and ships' knee braces. The outer sections have a king post roof, and the central mould loft floor is supported by a 13-bay collared queen post roof. Historically, the building was used for shaping and storing masts on the ground floor and for drafting plans in the spacious first-floor loft. The mould loft was extended in 1833 to include parts of the flanking bays and was used to layout HMS Victory in 1759 and HMS Achilles in 1860, the first all-metal warship in the world. From 1855, it served as a store. This is the last surviving timber mast house in a naval yard, showcasing ship-builders' techniques in its joints and members, and is part of a significant group of naval buildings within a complete Georgian dockyard.