C6 – Barrel vault

Building
techniques :
C6 – Barrel vault
Country :
Syria
PRÉSENTATION
Geographical Influence
Definition
Barrel vault
- Horizontal framework, semi-cylindrical
shape resting on load-bearing walls
- For the building, use or not of a formwork or
formwork supports.
- Used as passage way or as roofing (in this
case, the extrados is protected by a
rendering).
Environment
One finds the barrel vault in the majority of the Mediterranean countries studied. This structure is usually used in all types of environment: urban,
rural, plain, mountain or seaside.
Associated floors:
Barrel vaults are used for basement, intermediary and ground floors for buildings and public structures. This technique is sometimes used for
construction of different floors.
In Syria, the barrel vault is found in urban and rural environments. It is common in all types of environments except mountainous areas.
Associated floors:
In Syria, this technique of construction is used in house cellars and basements, it is also found on ground floors in the shops, workshops and in
old souks.
Illustrations
General view:
Detail close-up:
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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C6 Syria – Barrel vault
CONSTRUCTION PRINCIPLE
Materials
Illustrations
Nature and availability (shape in which it is found)
For the construction of barrel vaults, the most often used materials are limestone and
terracotta brick in all the studied countries. Other kinds of stones are also used according to
the local availability in materials ( schist and granite...). The materials added for the filling of
the interstices of the extrados, or for the composition of mortars are: broken brick, lime,
gypsum plaster, gravel or pieces of broken pots and coal debris.
In Syria, the stone is the principal material to make barrel vaults. It is used in two shapes:
either well cut and dressed to produce a smooth and orderly intrados, or rough stones which
produce an irregular intrados called “Gamce” locally.
The barrel vault is laid in mortar masonry; the filling material is made up primarily of earth.
Modules, Dimensions, Dose ratio
The barrel vault is masonry laid in mortar: the modules are assembled one against the other
according to a sloped plane determined by a radiant wire that shows the angle of each section
from the bottom of the vault to the key, and from the center of the arc. The stone or brick
modules which make up the vault can be cut so as to form a specific key for the vault (2 tilted
faces make up both a stone course and a bearing surface). They are often hardly outlined in
flat stone: mortar catches up any irregularities showing on the surface.
In Syria, the barrel vault is assembled with stones, sloped on a curve drawn by a fixed wire,
determining a ray up to the arch key. The dimensions of the stones of the cross vault are
approximately 35X30X25 cm and the thickness of the vault is 35-40 cm. In addition, the semi
cylinder arch of the vault can vary in shape and dimension. The vault can take on several
shapes: half-circle, Persian arch or horseshoe, depending on the positioning of the centre of
the arch or by drawing multiple arch centres.
As for the dose ratio, the mortar used is made of 70% earth and 30% of straw, sometimes
earth and lime.
Construction principle: perspectives, diagrams
Type of laying
Type of laying, use of a formwork, formwork supports
The building of the vault is generally carried out using a wooden formwork.
The latter is composed of at least two trusses (section of the vault), on which one fixes laths of
wood (sole-piece), the outside shapes the intrados of the vault. The formwork can also
produce a more approximate shape, which is then corrected with a bed of earth or sand...
Anchored directly in the walls (cross beam, retractable) or supported by bolders (projecting
stones left in place after laying ), this unit constituting " the formwork " is held by supports.
The laying of stones and bricks is made from the springer to the key by balancing the loads on
both sides of the vault axis. In the Mediterranean area, some techniques are freed from this
formwork system (low wood supplies? tools are considered as overly cumbersome?,
particular and local know-how?...). Building without formworks is possible with regular shaped
modules (terracotta brick, cut or not), well prepared mortars (adherence of bricks, hardening
speed...) and with a particular laying method. The latter seeks to limit the overhang of a key
stacking, by creating intermediary support joints, by slanting the laying axis
(springer/key/crown) towards the walls.
In Syria today, barrel vault is laid with a wooden formwork. The main formwork is semicylindrical, assembled lengthwise between two load-bearing walls, supported by horizontal
wooden boards and by vertical beams which carry the framework, taking on the shape of the
vault; the vault is constituted on top of this unit.
Trades
Trades, number of people necessary
The barrel vault is exclusively carried out by experts, mason, mason/stone cutter, or stone
cutter helped by assistants (significant handling, mortar to prepare...), and sometimes
assisted by a carpenter for the realization of the formwork.
In Syria, Several people of art are needed to make a barrel vault. Initially, a mason and
mason/stone-cutter are needed, along with several common masons to handle and prepare
the mortar and filling. Sometimes, it would be necessary to call upon a carpenter to make the
formwork.
Construction principle: type of laying, general
view and detail close-up
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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C6 Syria – Barrel vault
CONSTRUCTION PRINCIPLE (CONTINUED)
Tools
Illustrations
In addition to traditional mason tools, no particular tool is necessary for the building of the
vault in throughout the studied countries.
In Syria, the traditional tools of the mason used to make cross vaults are:
1. Hammers in several shapes.
2. Chisel.
3. Hammer with transverse edges: to shape and dress stones.
4. A trowel to spread the mortar.
Performances
Physical (span...).
This construction technique leads to span widths that range from 1 to 7 meters, for a
thickness that varies from 30 to 50 centimeters and can even reach 1 meter on the edges of
the vault in Tunisia.
In Syria, the span of barrel vaults varies considerably according to the type of construction
and the shape of the arch, but the most important point is to keep certain proportions between
the length, width and height. The span can be between 2 and 4 meters in houses and reach
up to 6 meters in old souks. The thickness of the walls varies according to the shape of the
arch; the thickness of the vault is approximately 40 cm.
Thermal - Acoustic.
For a stone construction, limestone in particular, the thermal and acoustic performances have
been reported from rather good to excellent by all the countries concerned. Considering the
significant mass of the vault, its thickness, the materials used in its construction, this piece of
work has remarkable thermal and acoustic insulation qualities.
In Syria, the thickness of this stone roofing allows good performance, the earth and mortar
filling is thick and ensures both thermal and acoustic insulation.
Tools
Construction principle: performances.
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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C6 Syria – Barrel vault
ASPECT, PATHOLOGY
Aspect
Illustrations
Finishing, associated roofing.
The intrados of the vault is generally covered with a rendering. However, in the case of ashlar
vaults or carefully laid bricks, the facing can be left bare. In the case of a vault for a passage
way, the extrados of the vault generally does not get any particular processing; haunches are
frequently filled with various materials (quarry rubble, building site residue), the unit gets a
system to seal the ground. In the case of a roofing vault, the extrados of the vault has regular
lines, and receives an elaborate waterproofing rendering.
In Syria, after the completion of the barrel vault one fills the gaps between the stones shaping
the vault, to a thin and smooth mortar is spread on the extrados. As for the intrados, the slope
is shaped with two layers of lime rendering:
- the first called locally "le cloue" is made up of 50% earth and ashes plus 50% limestone and
left to rest for 3 days before use.
- the second is a smooth rendering: 2/3 lime plus 1/3 hemp, stone powder and soap, left to
rest for 5 days before use.
Ageing pathology
Linked to materials and climatic conditions :
As for stone or brick masonry, pathologies related to materials originate in water (capillarity,
infiltration, condensation...), which dissolves the mortars and weakens them. The control of
water infiltration is more significant in the case of the vaults; Beyond the dissolution of the
mortars it is necessary to note direct erosion, that can affect the rendering mortars.
In Syria, barrel vaults are affected by the climate and moisture which deteriorate and then
damage the external rendering of the vault. It is necessary to carry out repairs with rendering
before the climate affects the stones, and causes any partial damage to the vault.
Linked to the technique:
The vaults produce lateral thrusts, that are weak in the case of the barrel vault. However, not
taking this strain into account in dimensioning load bearing walls leads to a cracking of the
vaults, sometimes even collapse.
In Syria, no ageing pathology linked specifically to the vault technique of was reported; it is
however necessary to check the thickness of load-bearing walls because of lateral thrusts that
can cause collapse.
Ageing pathology: linked to materials and to
climatic conditions.
ASSOCIATED WORKS
Openings
Small openings can be made to ventilate the rooms (in Palestine and Israel) or to give light,
particularly in the souks (Tunisia). The rectangular openings are between 0,5 and 1 meter. A
peripheral frame (rafter) distribute the loads.
In Syria, barrel vaults can have high openings in particular cases, e.g. in a covered souk, but
not in houses. These openings are square or rectangular, distributed lengthwise, contributing
to ventilation and lighting.
Connection framework - Vertical Structure (wall):
No type of connection was reported: the vault is assembled in the continuity of the walls, at
the same time and by the same people. The two works are indissociable.
In Syria, on the last top row of load-bearing walls and beginning the vault, one lays stones
called "main stones" which overhang approximately 2 cm and carry the other superimp osed
stones which constitute this vault.
Associated works : connection framework vertical structure (wall)
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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C6 Syria – Barrel vault
REAL IS A T I O N D E S C R I P T I O N
In Syria : (Text in French)
Les voûtes en berceau sont posées au moyen d'un coffrage en bois construit au préalable sur la longueur ou une partie de la voûte, il vient
s'appuyer sur deux murs porteurs.
Le coffrage en bois est élevé en deux étapes : tout d'abord, des planchers en bois sont montés horizontalement et fixés sur les murs porteurs
supportant ainsi des piliers en bois qui portent le coffrage semi cylindrique qui prend la forme de la voûte en question.
Le procédé est complété par la superposition des pierres qu'elles soient taillées ou brutes avec des dimensions de 35x30x25 environ, ces pierres
sont superposées au fur et à mesure que se dessine le profil de la voûte en utilisant le mortier comme liant.
On commence la construction de la voûte par les deux côtés des murs porteurs en posant une rangée en saillie, puis en montant la paroi avec
son profil pour arriver jusqu'à sa clé. En cas d'utilisation des moellons, les vides sont comblés par de la terre, des petites pierres et du mortier
pour avoir une surface lisse.
Le tout est couvert par une autre couche de terre d'épaisseur entre 50 et 70 cm, formant ainsi le plancher de l'étage du dessus.
En cas d'utilisation des moellons, l'intrados de la voûte est revêtu par un enduit de chaux sur trois couches : deux rugueuses "Cloue et Btaneh" et
une lisse "Dhara".
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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C6 Syria – Barrel vault
U S E , E V O L U T I O N AND T R A N S F O R M A T I O N
Use
Types of buildings
This framework is used for all types of construction : housing, monuments and buildings public, facilities (mosques, souks, hammam, trade, craft
industries, caravanserais)
In Syria, barrel vaults are used in all types of buildings in old cities for long shaped constructions, they are also used for the roofing of
passageways, alleys, Iwans in houses and finally in old souks.
Period when the technique first appeared. Period when the technique is in use – still used today or disappeared :
This construction technique has existed since antiquity. It is on the verge of disappearing everywhere, when it hasn’t already completely
disappeared. It is used, however, in the restoration of certain buildings.
In Syria, the oldest constructions using this technique in old cities go back to
the Byzantine period. This technique remained in use till the end of
th
the 19thcentury. The oldest examples are in old cities and go back to the 10 century. Nowadays, the use of barrel vaults is maintained and limited
to restoration and restoration campaigns.
Reasons why the technique disappeared or has been modified :
The reasons evoked by all the countries are mainly; high cost, slowness of work and skilled labour required for the technique, and a loss of knowhow related to this technique.
In Syria, the emergence of new construction techniques, like reinforced concrete for roofing, together with relatively high cost and lack of
specialized labour have led to a disappearing of this technique in new constructions.
Evolution / Transformation
The materials
The stone barrel vault with lime mortar is used only for rare works of restoration. It has been replaced by hollow floors, using reinforced concrete
girders, soldered trellis, cement. All these new replacement materials replace, on the commercial market, the traditional materials used in the
construction of masonry with mortar. In certain cases, we can consider that it is not completely lost as far as the shape is concerned, and it simply
changed because of the emergence of brick, especially hollow brick, that generalised and replaced stone.
In Syria, there is no major change in the materials used for barrel vaults. On the other hand, cement has replaced lime or earth in the composition
of the mortar used as binding material.
The technical aspects
The hollow bodied floor is the covering system that replaces the barrel vault. The barrel vault is built as a whole with the load bearing wall, without
interruption, whereas new floors are built with reinforced concrete beams that are not embedded in the walls: they thus constitute mere filling
walls, made with hollow bricks, and do not play any structur al role. It is therefore recommended to embed the beams using pins, and sink the steel
elements in an uninterrupted reinforced concrete blanket over the whole floor frame.
In Syria, the proportions of materials are the same but only for restoration. The same old tools are still used for the construction or restoration of
barrel vaults to obtain the same aspect. There is nonetheless an evolution: the stones used are machine cut and shaped in a factory rather than
on the site.
Evaluation of materials and replacement techniques
- On an economic level and given the speed of production, the use of reinforced concrete beams is amply satisfactory
- Reinforced concrete beams undergo rather significant strain under the effect of temperature variation
- Replacement materials are more vulnerable to water infiltration, and less resistant in time
- On an aesthetic level, the aspect of finishing of contemporary reinforced concrete vaults is completely different from traditional crossed vault in
stone or brick.
- Mechanically, the reinforced concrete floor framework undergoes traction, which is not compatible with the bearing structures in masonry which
undergo compression: cracks appear at the contact point of the two structures .
In Syria:
- The use of cement mortar instead of lime is faster, thus more profitable on an economic level, and time saving.
- Replacement materials are more resistant to water infiltration.
This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States
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