, November 1916 outside their Nissen hut billets in
Rouen, France, 18 June 1918. Note the wartime censorship of the sign on the door. 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 slightly more than a semi-circle so that the bottom of the hut curves inwards slightly. The exterior is formed from curved
corrugated steel sheets by , laid with a two-corrugation lap at the side and a overlap at the ends. Three sheets cover the arc of the hut. They are attached to five wooden
purlins and wooden spiking plates at the ends of the floor joists. The purlins are attached to eight T-shaped ribs () set at 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
hardboard attached to the ribs. Sometimes corrugated
asbestos cement sheeting was used. If required, the space between the lining and the exterior may be used for insulation and services. The walls and floors rest on foundations consisting of stumps with sole plates. On these are bearers and joists at centres. The floor is made from
tongue-and-groove floorboards. At each end the walls are made from a wooden frame with
weatherboards nailed to the outside. Windows and doors may be added to the sides by creating a dormer form by adding a frame to take the upper piece of corrugated iron and replacing the lower piece with a suitable frame for a door or window. Nissen huts come in three internal spans (diameters)—, , and . The longitudinal bays come in multiples of , allowing the length of the cylinder to be any multiple of that. The corrugated steel half-circles used to build Nissen huts can be stored efficiently because the curved sheets can be cupped one inside another. However, there is no standard model of Nissen hut, because the design was never static and changed according to demand. ==History==