Building History

This magnificent building has been owned since late 2011 by English Heritage who then undertook a detailed survey, followed by a complete restoration in 2014.

The repairs were made by Owlsworth, a firm specialising in works to historic buildings, under the supervision of Ptolemy Dean Architects. Previously repairs had been made in the late 1980s by McCurdie, a firm of specialist craftsmen in timber buildings.

The Royal manor pre-dates the Norman Conquest and was acquired in 1391 by William of Wykeham as part of the endowment for his foundation of Winchester College. By 1547 the land was owned by Sir William Paget, whose family farmed it until the 18th century, and it remained in agricultural use until the late 1970s.

Work on the barn itself was begun in 1424-5 when William Kyppyng and John atte Oke inspected timber near Kingston-on-Thames on behalf of Winchester College. It was at least partly completed by 1426 and the tilers were paid for finishing their work in 1427. It replaced earlier storage barns that appear to have come to the end of their economic life and its construction led to an increase in the income from the manor. Documents relating to its planning and construction survive at the College.

Building Description

At 193ft in length, 39ft wide and 37ft high the barn is the largest medieval timber-framed barn to survive in this country. Over 95% of the structural timbers and over half the cladding are original.

The construction of a building on this scale, with the use only of axes, saws and adzes, was an awesome undertaking. It used a complex but effective system of bracing not unlike the nave and aisles of contemporary Gothic church buildings with, in this case, only oak dowels to secure it.

There are 12 bays and three entrances from the east (in the 3rd, 7th and 10th bays from the south), each of which had threshing floors. The base of the walls is a low plinth of natural ferricrete (which slopes 1ft north to south so all the trusses lean a little) and the huge inverted tree trunks of the main posts stand on blocks of Reigate stone. The roof is covered with new hand-made clay peg tiles hung on riven oak battens.

Further details can be found at https://www.english-heritage.org.uk/visit/places/harmondsworth-barn/history and in The Great Barn of 1425-27 at Harmondsworth, Middlesex by Edward Impey with Dan Miles and Richard Lea (Swindon: Historic England, 2017).