The Great Barn, Harmondsworth: Medieval Gem
The Great Barn at Harmondsworth is the largest standing medieval timber-framed structure in Britain.
Built in 1425, it's regarded as an outstanding example of medieval carpentry.
This Grade I listed barn ranks alongside the Houses of Parliament and Westminster Abbey for its exceptional architectural and historic interest.
It is one of the nation's most important architectural treasures - and it was dubbed the "Cathedral of Middlesex" by Sir John Betjeman.
It was built with the same skill and attention to detail as the great churches and palaces in England.
The barn at Harmondsworth was built in 1425–7 on land bought by William of Wykeham, Bishop of Winchester.
It was used mainly to store cereal crops before threshing, and it remained in agricultural use until the 1970s.
At 58 metres long and 11.4 metres wide, the barn is one of the largest ever known to have been built in the British Isles, and the largest intact medieval timber-framed barn in England.
It was originally a much larger structure, with two wings, but the north wing was dismantled in 1774 and rebuilt in the now-demolished hamlet of Heathrow, on the site of the modern airport.
The vast majority of the surviving structure is original; it has been estimated that 95 per cent of the timbers, including the external weatherboarding, have survived from the original building.
It has been described by English Heritage as "a supreme example of late-medieval craftsmanship – a masterpiece of carpentry containing one of the best and most intact interiors of its age and type in all of Europe.
The barn's main posts are made of oak. Each is about 14 inches square and sits on a block of Reigate sandstone, a common building material in medieval London.
The posts were cut into shape using axes, adzes and saws, the marks from which can still be seen in some instances.
The builders cut and fitted the timberwork together on the ground and scratched Roman numerals, called assembly marks, on the joints to indicate where pieces of timber were to be combined.
The use of aisles enabled the barn's architects to increase its width and by doing so, provided the maximum space for threshing floors.
The longer the barn was, the more threshing floors could be provided.
English barns went through an evolution in the number of threshing floors; the earliest had just one central floor, a design that became the commonest to be found in Britain.
Harmondsworth Great Barn is unusual in having three threshing floors, allowing much more grain to be threshed at one time.
By 2006, time was catching up with the Great Barn.
Rainwater had started to seep into the building, roof tiles were falling off, weeds sprouted amid its 700-year old timbers, and no fire alarm system or fire-fighting equipment had been installed.
Historic agricultural buildings, especially old barns, are especially vulnerable to damage, accidental or otherwise.
In 2004 and 2005, a series of fires at another huge barn, that at Frindsbury, near Rochester, Kent, destroyed four of its 13 bays. Frindsbury Barn dates from 1403.
Despite pressure from English Heritage and local campaigners, the owner of Harmondsworth's Great Barn failed to carry out any repairs.
In 2009, in the wake of coverage in Cornerstone magazine, published by the Society for the Protection of Ancient Buildings (SPAB), English Heritage served an Urgent Works Notice on the owner, requiring repairs to be carried out.
The barn's owner still refused to co-operate, so English Heritage carried out repairs itself. While seeking to recover the full cost of these repairs from the owner, English Heritage struck a deal with Harmondsworth Barn Ltd to buy the building for £20,000.
It was bought by English Heritage in 2011.
Today, the barn is open to the public, you can check the opening hours via the English Heritage website.
The barn is accessed via the small spur road off High Street to the right of 'The Five Bells' public house.
More about the Structure
Some of the pairs of main posts were made from the trunks of very large individual trees which were cut in two.
They were all placed upside down, relative to the original direction of the tree.
This was because the bottom of a tree is always wider than the top; the greater width was needed to accommodate the joints with the beams that support the roof.
Despite the care that the builders took to get the joints right, they may have made some mistakes along the way, as some of the timbers have holes for pegs and mortises that were never used.
Alternatively, the timbers may have been reused from another construction.
Because such barns tend to be both long and high, they experience high structural loads from the wind.
They therefore have numerous internal braces, acting in much the same way as buttresses, to strengthen the structure.
This gives the barn its distinctive internal appearance, with a lattice of beams and braces holding up the roof.
The techniques used in its construction are similar to those employed on the great cathedrals being built at the time, and some of the same craftsmen were probably involved.
The floor of the barn was originally made of hard-packed flint gravel held together with iron panning, excavated from a local gravel deposit, which was used as a more readily available alternative to stone.
In subsequent years, it was repaired with brick, tile and, ultimately, cement, obscuring the original appearance of the floor.
An indication of how it would have looked can still be obtained from the outside of the west side of the barn.
The design of the barn has provided inspiration to a number of architects in the 19th and 20th centuries who were involved with the Gothic Revival movement.
Sir George Gilbert Scott visited the barn in 1850 and sketched it, using its design as the basis for proposals for the new ChristChurch Cathedral in New Zealand.
The landmark has some great reviews on TripAdvisor.
One recent visitor, said: “An amazing building. Difficult to believe that it's over six hundred years old, some of the timbers are even older than that. Well worth a visit!”
Another person added: “I found out about the existence of the Great Barn after reading about the planned new runway for Heathrow airport.
”Thankfully, the barn will be saved, but will be right next to the perimeter fence.
”If you love history, or just beautiful structures, you MUST visit. It's free and it is amazing. Check dates before you go.”
If you’d like to visit, the address is: The Great Barn, Manor Court, High Street, Harmondsworth, Greater London, UB7 0AQ.
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