A timber roof structure with a glazed lantern
The single-storey exhibition building has a pitched roof, which rises to 7.5m high at the ridge. A glazed roof lantern, 8.8m long, is set in the ridge above the hall to direct natural light onto the 'submerged' ship below.
The timber upstand of the lantern rests at each side on a truss, which spans 17.6m to paired Douglas fir columns at the gable ends of the hall. Each truss has a top chord of paired 150mm square Douglas fir sections connected with steel plates to a central steel plate strut and a solid rod tie. They are braced with diagonal steel rods to prevent twisting. The trusses create a clear columnfree space for the exhibits.
The pitched roof of the building is supported by a series of canted exposed trusses at 4.4m centres, each with a 150mm square timber top chord, a central steel plate strut and a solid rod tie. At the eaves the trusses rest on 150mm square wall posts. At the lantern they are fixed to fabricated connection plates.
These had to incorporate bearing and tie plates for the truss as well as connector plates for the main purlins, welded together in a single component.
A fabric baffle is suspended below the lantern to direct natural light onto the ship. It is fixed to a braced steel frame, which incorporates a row of horizontal security bars at 120mm centres.
The lantern is glazed and has opening vents at the sides to provide through ventilation.
These work in conjunction with opening vents in the walls below the eaves. Air passes via screened louvres set in the ship-lap boards through opening aluminium vents.
The walls also contain fixed glazed lights, which are protected with a single vertical security bar.