Extended information on the architecture of Notre Dame de Paris

— Nick Breur —



The original plan
The construction of the cathedral of Notre Dame de Paris began between 1150 and 1155. Despite the fact that construction required many decades under supervision of a succession of masterbuilders the basic plan was implicit in the work done by the first builder who directed work on the chevet from around 1155 untill perhaps 1170. He designed one of the strictest floorplans of his time. He excluded all apsidal chapels or additional spaces. Instead, he created a cruciform main space with a uniform character. The transepts, as so often in the Paris region, did not project beyond the aisle wall. The plan called for a double-aisled columnar basilica, perhaps reflecting the plan Suger had intended for the nave at Saint-Denis, although it might have been equally inspired by the five-aisled Merovingian cathedral of Saint-Etienne. Two double-rows of free-standing columnar pierses, culminating in the two hemicycles of the double ambulatory, are only interupted by the transept and the crossing with its four piers. On the east end the builder eliminated the gentle bulges of chapels (as in Saint-Denis) in favour of a smooth continuous curve with wall responds on the inside and buttresses on the outside. Further, in a conception that looked ahead to the plan of the nave, he preserved a regularity of spacing between the columns, even devising a complex vaulting scheme for the ambulatory ceilings that eliminated devisions between the bays. In effect, the builder sacrificed the compact unity of the chevet in order to achieve a wonderful sweep of space around the east end, visiually linking it to the western extension of the cathedral. The interior elevation was originally of four levels, with an arcade of columnar piers; a tribune, originally covered with transverse barrel vaults, and lit by round windows; decorative oculi opening into the tribune roof spaces; and small clerestory windows. The high vaults are sexpartite, covering double bays. Although these vaults are very high the walls which supports them are thin and articulated by very slender shafts. The ornament chosen to articulate the interior spaces was an inportant issue because the length and height of the building meant that the builder had to deal with huge walls. He had to balance horizontal and vertical lines in a grid so that neither overpowered the other. As usual in those days he found the solution in devising a systhem of ornament that created a sense of structural lines. But at Paris the moldings and arches are exaggerately thin. Not because the builder wished them to be overlooked, the thin ornament was part of a general strategy of emphasizing the wall surface in stead of concealing it as at comtempory buildings like the Laon cathedral and the Saint-Denis chevet. The builder sought this effect in other details as well. Relatively large area's of blank wall surface were left around the oculi and windows. This wall did not suggest mass or thickness. The very thin moldings created the impression of a delicate thin wall, a membrane spread between wall shafts, a smooth surface with little sens of depth. This implied thinness of wall is one of the most important aesthetic aspects of Notre Dame, and one that was continued and exaggerated still more by the second master.
The church was planned to be the tallest space in Gothic architecture. Its vaulted ceilings rise some 33 meters above the floor, more than eight meters higher than those of any of its early Gothic predecesors. The relative increase in height over previous buildings, more than one-third, was the greatest of the entire era. Nevertheless the structural configuration was essentially similar to that of earlier, smaller churches. The outward thrust of the vaults against the high window wall (the clerestory) was resisted only by stone quadrant arches hidden under the sloping roof of the adjacent gallery. The first Paris builder seems to have been unprepared for the decrease of light reaching the floor of the church resulting from its significantly higher walls.

The eastern parts
Generally speaking, the building of the church took place from the east to the west. The first masterbuilder constructed the ambulatory and most of the choir conform the original planning. Changes in the vaulting of the choir from bay to bay reveal that the masons were experimenting with ways to achieve this vaulting even as they constructed it. Designers of medieval buildings learned from experience. They used the actual buildings to ascertain the structural behaviour of a design. The observation of cracking in weak, newly set mortar, for example, often led to structural modifications that were undoubtedly an important source of design innovation.
The choir and transept were completed in 1182.

The nave
The work on the nave began circa 1170-75. Beginning with the upper stories of the chevet that also date from the early 1170s, the direction of the construction passed to a second builder. This builder began the nave, increasing its height and width. He was a master engineer. Although stone vaults had never been attempted at such heights, these vaults are amongst the finest and most accomplished medieval stonework, quite different in that regard from the chevet. The navebuilder also faced the technical problems imposed by the ambitious design: he introduced flying buttresses in Paris and he redesigned the gallery walls. But the basic schema followed that laid out by the first builder. Even the moulding profiles for the nave were clearly based on those originally used in the chevet.
The problem of the darkness of the central space must allready have been apparent when the choir was finished, because in the subsequent construction of the nave the second builder raised the height of the gallery vaults and enlarged the gallery windows.
At Note Dame flying buttresses were first used in the nave. In designing the somewhat wider nave, with its lighter and more open structure, the Paris builders evidently decided that the quadrant arches were insufficient to support the high clerestory. The increased width meant that the outward thust of the vaults was greater than the thrust in the choir. The basic idea, bracing the wall with quadrant arches to contain the outward thrust of the stone vaults and timber roof, had precedents in the chevet where the quadrant arches hidden by the gallery roof were intended to support the high window wall. Although similar in structure to these concealed arches, the flying buttresses are fully exposed and supported the wall at a higher level. The introduction of the flying buttress may also have had another reason. In building the choir the craftsman must have become aware of a new problem for which experience with lower churches could not have prepared them: wind speeds are significantly greater at higher elevations. Wind pressure, it is now known, is proportional to the square of windspeed, and so it has a much stronger inpact on tall buildings. Concern for wind loading may have been the principle reason for the builder of the Paris nave to introduce the flying buttress, just before 1180. Archeological evidence suggests that the original buttressing scheme included two separate tiers of flying buttresses: an upper tier above the gallery roof to brace the high clerestory wall and a lower tier to strengthen the outer gallery wall and to help resist the outward thrust transferred by the upper fliers. The upper fliers must have abutted the main wall at a point about halfway up the original window opening.
Flying buttresses anable the builder to contain the greater thrusts produced by the wider spans of flatter vaults and by windpressure, while at the same time reducing the weight of the walls by opening wider clerestory windows. As an elegant solution to the problem of building on a grand scale without massive walls, this innovation spread rappidly. Before this time flying buttresses were quite generally used, but in a casual manner, when trouble developed in the vaulting. By the time when the nave of Paris Cathedral was built, the new Gothic vaultings had shown that they needed buttressing even more than the older and heavier Romanesque vaults. The experience gained at one building site was transmitted to other construction projects: the earlier building acted as an approximate model to confirm the stability of a new design. In less than two decades the flying buttress became the stylistic hallmark of Gothic Building.

The 13th-century rebuilding
The developments in gothic architecture went fast. By the time the nave was finished the building was allready oldfashioned. Beginning in the 1220's an extensive rebuilding took place in which the clerestory and the buttressing scheme were changed dramatically. It was an effort to allow more light into the cathedral. The changes in the design of the gallery that were made so far to dispel the darkness in the church were insufficient and this led to the dicision to enlarge the clerestory windows to their present size. To lower the base of the windows it was necessary to lower the roof and outer walls of the gallery. The builders then also modified the flying buttresses. The upper flying buttressses were replaced by the buttresses that are still seen today: giant fliers that span both side ailes. This major redesigning may have been nescessary because the original buttresses were structurally part of the gallery wall that was changed. However, it is more likely that they were a response to structural problems inherent in the original design. Modern experiments have shown that after particulary severe storms cracking of the medieval mortar would have been apparent in two regions of the windward buttressing: where the upper fiers abutted the clerestory and where the lower fiers joined the gallery wall. It is doubtful that major problems would have arisen because repairs after every great storm would have prevented general deterioration. Such regular maintenance, however, would have been difficult because the regions were relatively inaccessible. The 13th-century rebuilding effort eliminated these regions of localized tension. The point of abutment of the new giant fliers with the clerestory was considerably higher, and they also significantly reduced the thrust in the gallery-level fliers. On groundlevel the builders took advantage of the enlarged buttresses by using them as separation walls for chapels that were build between them. The need for chapels reflects the growth in civic welfare and conciousness. Guilds and rich families could afford having their own place for praying or burrial. The facade walls of the transepts were brought in line with the new outer walls of the nave and the choir. The chappel windows are larger than the original aisle windows must have been but the effect on the lightening of the central space is diminished by the larger distance. Whereas the structural problems of the original flying buttresses were effectively solved, the benefits derived from the larger windows were at best slight. As anyone who has visited Notre-Dame de Paris will remember, the transept excepted, it remains a dark building.