A flying buttress is a specific form of buttressing most strongly associated with Gothic church
architecture.
The purpose of any buttress is to resist the lateral forces pushing a wall outwards by
redirecting them to the ground.
The defining characteristic of a flying buttress is that the buttress is not in contact with
the wall like a traditional buttress; lateral forces are transmitted across an intervening
space between the wall and the buttress.
Flying buttress systems have two key components - a massive vertical masonry block on the
outside of the building and a segmental or quadrant arch bridging the gap between that
buttress and the wall.
History Although fully-fledged flying buttresses only
developed in the Gothic period, they are described in the Bible in the Book of Ezekiel, chapter
41, verses 6 and 7, as part of the detailed design of a new temple, and architectural
precursors can be found in Byzantine architecture and in some Romanesque buildings, such as
Durham Cathedral, where quadrant arches were used to carry the lateral thrust of the stone
vault over the aisles.
However these arches were hidden under the gallery roof and only transmitted the forces
to the massive outer walls.
By the 1160s, architects in the Île-de-France were employing similar systems but with longer
and finer arches running from the outer surface of the clerestory wall, over the roof of the
side aisles to meet a heavy vertical buttress rising above the level of the outer wall.
The main advantage of such systems is that the outer walls no longer need to be heavy
and massive enough to resist the lateral thrusts of the vault.
Instead the wall surface could be reduced, with the vertical mass concentrated into external
buttresses.
Early flying buttresses tended to be far heavier than is required for the static loads involved,
as for example at Chartres and around the apse of the Basilica of St Remi in Reims,
which is thought to be among the earliest examples still surviving in its original form.
Later architects progressively refined these designs and slimmed down the flyers until
typically they were constructed from no more than one thickness of voussoir with a capping
stone above it (see for example the cathedrals of Amiens, Le Mans and Beauvais.
Later Gothic buildings continued to use flying buttresses but often embellished them with
crockets on the flyers and figural sculpture in niches or aedicules set into the buttresses.
Renaissance and later architecture eschewed the flying buttress in favour of thick-wall
construction.
However the design was revived by Canadian architect William P. Anderson to build lighthouses
at the beginning of the 20th century.
Construction
To build the flying buttress, it was first necessary to construct temporary wooden frames
which are called centering.
The centering would support the weight of the stones and help maintain the shape of
the arch until the mortar was cured.
The centering was first built on the ground by the carpenters.
Once that was done, they would be hoisted into place and fastened to the piers at the
end of one buttress and at the other.
These acted as temporary flying buttresses until the actual stone arch was complete.
Because the majority of the load is transmitted from the ceiling through the upper part of
the walls, making the buttress as a semi-arch extending far from the wall provides almost
the same load-bearing capacity as a traditional buttress engaged with the wall from top to
bottom, yet in a much lighter and cheaper structure.
And because the flying buttress relieves the load-bearing walls with a much smaller area
of contact, much larger voids are able to be built into those walls, such as for windows,
than would otherwise be possible.
Often on Gothic churches, two arched 'flyers' were used one above the other.
In such cases the lower flyer is designed to take the lateral force of the vault while
the upper one resists the effect of wind-loading on the roof.
The vertical buttresses at the outer end of the flyers were often capped with pinnacles
that provide additional vertical loading to help resist the lateral thrust transmitted
by the flyer.
Gallery
Remedial
Another application of the flying buttress is to prop up a leaning wall in danger of
collapse.
An example is found at Chaddesley Corbett, where a flying buttress has been added as
a more practical option instead of dismantling the leaning wall and rebuilding it.
The aisle was built in the 14th century, and dismantling it would be a major work.
See also Buttress
Cathedral architecture Flying arch
Gothic architecture Seismic retrofit
Notes ^ For the mechanics of how flying buttresses
work in practice see the pioneering study by Alan Borg and Robert Mark in "Chartres
Cathedral: A Reinterpretation of Its Structure", in The Art Bulletin, Vol.55, No.3, pp.367-372
^ John James, "Evidence for flying buttresses before 1180", in Journal of the Society of
Architectural Historians, Vol. 51, No. 3, pp. 261–287.
^ Prache, Anne, "Les Arcs - boutants au XIIe siècle", in Gesta, Vol. 15, No. 1, pp. 31–42
^ Russ Rowlett, Canadian Flying Buttress Lighthouses, in The Lighthouse Directory.
^ Alex Lee, James Arndt, and Shane Goldmacher, Cathedral Architecture.
^ Mark, R. & Jonash, R.S., 'Wind Loads on Gothic Structures' in Journal of the Society
of Architectural Historians, 29:3, pp.222-230.
References Chisholm, Hugh, ed.. "Flying buttress".
Encyclopædia Britannica.
Cambridge University Press.