Nissen hut

A Nissen hut is a prefabricated steel structure, made from a half-cylindrical skin of corrugated steel. Originally designed during the First World War by the engineer and inventor Major Peter Norman Nissen, it was used extensively during the Second World War.

A Nissen hut is made from a sheet of metal bent into half a cylinder and planted in the ground with its axis horizontal. The cross-section is not precisely semi-circular, as the bottom of the hut curves in slightly. The exterior is formed from curved corrugated steel sheets 10 feet 6 inches by 2 feet 2 inches (3.2 × 0.7 m), laid with a two-corrugation lap at the side and a 6 inch (15 cm) overlap at the ends. Three sheets cover the arc of the hut. These are attached to five 3 × 2 inch (7.5 x 5 cm) wooden purlins and 3 × 2 inch wooden spiking plates at the ends of the floor joists.

The purlins are attached to eight T-shaped ribs (1¾ × 1¾ × ⅛ inch; 4.5 × 4.5 × 0.5 cm) set at 6 feet 0.5 inch (1.8 m) centres. Each rib consists of three sections bolted together using splice plates, and each end is bolted to the floor at the bearers. With each rib are two straining wires, one on each side, and a straining ratchet (or in some cases a simple fencing wire strainer). The wires are strained during construction. The straining wires do not appear in the original Nissen patent.

The purlins are attached to the ribs using a "hook" bolt, which hooks through a pre-drilled hole in the rib and is secured into the purlin. The hook bolt is a unique feature of the Nissen design.

Interior lining could be horizontal corrugated iron or material like Masonite attached to the ribs. Sometimes corrugated asbestos cement sheeting is used. The space between the lining and the exterior may be used for insulation and services, if required.

The walls and floors rest on foundations consisting of 4 × 4 inch (10 × 10 cm) stumps with 15 × 9 inch (38 × 23 cm) sole plates. On these are 4 × 3 inch (10 × 8 cm) bearers and 4 × 2 inch (10 × 5 cm) joists at 2 feet 10 inch (86 cm) centres. The floor is made from tongue and groove floorboards.

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