Duxford: Building 78 (Hangar 5)

Aircraft hangar at Duxford, one of three identical hangars built between 1917 and 1918 under War Office Directorate of Fortifications and Works Drawing Number 332/17, designed by Lieutenant-Colonel BHO Armstrong of the Royal Engineers. The southern annexe was extended in 1930 and the northern annexe in 1935.

The building comprises paired sheds, each spanning 100 feet with a clear height of 25 feet. The sheds are arranged on an east-west axis and are the westernmost of three hangars standing in line on the north side of the airfield. The building is 170 feet in length overall, divided into 15 bays with brick buttresses spaced at 11 feet 4 inches intervals supporting Belfast roof trusses.

The exterior features Esavian sliding and folding doors with diagonal timber boarding at both the east and west ends, which run on overhead tracks with a deep apron above, terminating in brick pylons at each corner. Personnel access is provided by wicket doors within the aeroplane doors. The north and south walls have raking brick buttresses rising to the eaves, with half-brick curtain walls between. The end bays are plain, while the remaining 13 bays contain full-width steel casement windows in 27 panes set as high clerestory lights. Alternate bays incorporate additional six-pane pivoted opening sections. A deep apron band runs above these windows. The roofs are profiled steel in flat segmental form with continuous ridged patent glazing roof lights spanning the central 13 bays, and additional patent glazing lines each side of the central valley. Eaves have a plain painted fascia with gutter. Above the horizontal apron to the door track is a flat segmental pediment to each shed, featuring close-set vertical joint divisions to metal cladding and a wide central ventilation louvre.

At the north-east corner, the brick pylon has been modified to form part of a bomb dropping training tower, featuring a round-headed open arch on the north side, a corbelled arch on the west side, and a brick box superstructure with an open west side and flat concrete-slab roof.

Lean-to annexes flank the sides. The northern annexe comprises two sections: a seven-bay section spanning bays five to twelve with nine-pane steel casement windows with pivoted central sections to each bay, and a three-bay section spanning bays 13 to 15 with two-light steel casements with square pane glazing. Bays four and twelve accommodate late-twentieth-century double doors with glazed top panels and two-light fanlights. The southern annexe has a four-bay range built around 1930 spanning the width of the first four bays, with two three-light steel casements either side of an off-centre doorway. Set back is an original seven-bay annexe spanning bays five to eleven, with its third and fourth bays accommodating louvered double doors to the boiler house and compressor room, while the remaining five bays each have nine-pane steel casement windows with pivoted central sections. Bay 12 contains a late-twentieth-century entrance door with glazed top panel.

The interior has paired sheds separated by a central row of brick oblong piers with narrow central openings to arched heads. Moulded stone corbels on each side carry the roof strutting. Running between the piers to support the gutter and provide stiffening is a series of diaphragm walls, one brick thick, on flat segmental arches. Each bay is divided by wooden-latticed Belfast roof trusses spanning from the central piers to the buttresses in the outer walls. All trusses are whitewashed, with a flat bottom chord and a bowed upper profile formed from straight members. All truss members are small-section softwood with doubled main members sandwiching a close-spaced diagonal grid infill. At the end supports, the trusses are strutted to shaped stone corbels, with the knee area strengthened by diagonal close-boarded sheeting. Five sets of simple cross bracing run longitudinally, with diagonal sheathing on small purlins carried to the roofing. The end bays have extra horizontal bracing to the bottom chord. Concrete floors throughout.

The building has been subject to late-twentieth-century alterations including fire curtains spanning the four westernmost bays of the south-side shed to partition an aircraft spray area. The four arched piers at this end and the aeroplane doors at each end have been fitted with protective screens, and ventilation flues with associated pipework have been installed.

Materials consist of brick buttresses, curtain walls and internal piers (all painted), and timber roof trusses covered with profiled steel sheeting. Annex roofs are of corrugated steel sheeting.