The Great Barn, Harmondsworth

The Great Barn at Harmondsworth

This is a barn built in 1426–7, substantially of that date, with later work of various periods including restoration by Peter McCurdy & Co. in 1987.

Materials and Construction

The barn is built with an oak frame and exterior cladding, though some modern softwood pieces have been introduced. The roof is covered with clay tiles of many periods. The aisle posts stand on blocks of Reigate stone. The sill walls are constructed of ferricrete (a local iron-rich conglomerate), flint, and brick, with some Reigate stone. The building contains abundant post-medieval ironwork of many periods.

Plan and Dimensions

The barn is oriented almost due north–south and measures 58.5 metres (192 feet) by 11.4 metres (37.5 feet). It consists of a broad central nave flanked by an aisle on each side, articulated transversely into 12 equal bays.

Exterior

The low sill walls are largely built of ferricrete in unusually large blocks, interspersed and galleted in flint. The dressings, originally of Reigate stone at the quoins and door-jambs, have been largely replaced in brick of many periods. The barn has three doorways, all facing east, none of which ever had a porch. Seven openings with single or double planked shutters have been inserted on the western side at various periods, all above sill-beam level. The western and eastern walls were originally covered with vertical oak boards fitted to rebates in the sill beam, wall-plate and main wall posts; approximately 80 per cent of this boarding remains, an exceptional survival rivalled perhaps only by the Kentish barns at Littlebourne (1307–27) and Frindsbury (1404). The north gable wall covering dates substantially from 1987, as does the south wall, the original having been fire-damaged in 1972.

Interior Structure

The main structure consists of large square-sectioned arcade posts with thickened jowled heads jointed to both arcade plate and tie-beam. The arcade posts are braced to the tie-beams by large slightly concave braces, with similar braces to the arcade plates. The main roof is a simple principal rafter with collar and crown-strut, and a butt purlin with windbraces but no ridgepiece. The aisles have ties which interrupt the wall plates and have a raking strut which engages with the principal rafter and clasps a single purlin for the aisle. The aisle trusses are braced by a pair of braces meeting under the aisle ties, and each truss has a sill beam which engages with the aisle walls at one end and supports the arcade plate at the other. The wall framing to the aisles consists of a centre stud and middle rail, resting on a high sill beam. The ends of the barn similarly have a centre post, a heavy middle rail set just above the aisle ties with subsidiary rails above and below. The half-hipped ends of the roof are supported by an arch-braced, intermediate, principal rafter collar truss, which receives the end of the purlins and supports the hip-rafters in mid-span. There is a small gablet above each hip.

Notable Structural Features

The carpentry is remarkable for a number of structural oddities. The butt-purlin joints to the principal rafter over the nave are formed of diminished haunch tenons arranged upside-down; although an inept arrangement, this represents a very early use of the diminished haunch tenon. The roof structure includes crown struts, which are both precocious and outside their normal geographical range. The aisle purlin is clasped by a raking strut, which is itself an early example (most dating from the 16th century). The aisle wall plates are tenoned into the sides of the aisle ties, perhaps the earliest such arrangement in Britain, although an odd one to use here, as this lacks longitudinal strength.

The framing shows evidence of changes of plan during construction, resulting from the failure of the door-positions in the timber-framing, as first set out (probably off-site), to match the positions of two of the doorways anticipated by the builders of the masonry sill-wall. In bays 8 and 11 (counting from the south), the sill-beam and mid-rail have been pieced in, while the empty mortices in the underside of the wall-plate were clearly intended to house the door posts, identifying these bays as the intended doorway positions. As completed, the doorways were placed in bays 7 and 10.

The building also has a notable range of apotropaic marks—symbols to ward off evil and bad luck—and an almost complete sequence of carpenters' assembly marks and other graffiti.