Historically, temple roofs have been made of wood or stone. The first option takes a lot of weight off the structure and transfers the load vertically to the support walls but, despite the advantages, this material requires constant upkeep and the risk of fire limits its lifespan. This is why roofs tend to be made of stone, a material that resolves the issues that wood poses but, on the other hand, comes with inclined forces that must be compensated. To resolve this problem, Romanesque architecture mainly used a juxtaposition of other vaults and very solid walls, while Gothic architecture, with taller, thinner constructions, used buttresses and flying buttresses.
For the Sagrada Família, Gaudí chose stone rooftops without any type of buttresses. Thanks to the mechanical system he designed, the columns are inclined depending on the load they bear and transfer it down to the base of the column without any need for external elements to compensate for the horizontal forces. Plus, from the beginning the Temple roofs were designed to have two layers: one is a vault and the other is the roof itself. This system insulates the Temple from the weather outside with a ventilated chamber, like an attic, as well as creating more space for different uses on the upper floor.
This strategy is used in all the roofs on the Temple, both on the side naves and the central nave. Nevertheless, the space inside the latter, as it is very vertical, is subdivided into three levels supported by the nave columns.
ORIGINS OF THE PROJECT
The project for the Temple roof, which has now been laid out, was taken from a study of the original documents, meaning the models, graphic and written documents from preceding generations, as well as original photos taken prior to the 1930s. At the same time, the solution for the roofs on the side naves, which have a very gentle slope, has been adapted to the verticality of the higher levels.
It is true that Gaudí left designs for many parts of the Temple in plaster models in various scales and in great detail. For the Temple roofs, the solution was laid out in a 1:25 scale plaster model when the last great modification of the naves was being planned. Unfortunately, this model was damaged in 1936.
The work to restore and recover the fragments that could be salvaged has allowed us to rebuild this model, which can now be seen in the museum, and establish the geometry of the elements in it. Today, we’ve used laser scanning technology to create a three-dimensional model that is very true to the original. This model, which can be edited on the computer to eliminate the parts that are not relevant, allowed us to reconstruct the geometry. At the same time, we have studied historical photos of these models using descriptive geometry to determine the proportions and measurements of the whole.
Regarding the graphic documents, it is worth noting the static graphic study of the temple by Domènec Sugranyes, one of Gaudí’s close collaborators, in 1923. This shows how the columns in the main nave work and how they are inclined to balance the loads coming down from the roofs on the central and side naves.
THE ROOFS OF THE CENTRAL NAVE: IN DETAIL
Gaudí proposed two large families of roofs for the Sagrada Família: the ones for the side naves and the ones for the central nave. The former are on top of vaults at 30 metres, above the side naves of the main nave, with a width of two modules on each side; on the naves of the transept, with a width of one module on either side; and on the apse. All of these roofs are quite horizontal. The roofs of the central nave, above both the main nave and the transept, however, are much more vertical, on 45-metre vaults.
Today, of this definitive solution Gaudí proposed for the naves of the Sagrada Família, we are finished with the 30-metre vaults on the apse and the transept and are starting preliminary work on the side roofs of the main nave. The side roofs on the main nave and the central nave still have to be built, although the executive project for them has recently been completed. The first level of these roofs, from 45 metres to 54 metres above street level, is the only one that connects directly to the inside space and is already complete. Work will soon begin on the other two.
Puig Boada, in El temple de la Sagrada Família, described these roofs: “The ones on the central nave, which are the tallest, are made up of a series of pyramids, one on each vault joist, joined together and with the window pediments in the middle of huge paraboloids.” Above the paraboloids, there are five shields, like those on the Nativity bell towers, inscribed with “Amen” and “Alleluia”. The lamp will complete this piece and be topped with a Tau. Natural light will come in through the openings behind the pediments, as well as the three windows on the flat faces between the paraboloids.
The columns of the central nave reach the level of the 45-metre vaults, where they link together to form the base to support the weight of the vaults and outer walls. From this level, the columns continue up to 60 metres with a simpler geometry, octagonal in shape, but the same diameter. The capital is defined by triangular planes and hyperbolic paraboloids, transitioning from the column to the vaults that create the second and third attic levels.
The last section of the columns, two for each module, will be done in reinforced concrete, just like those for the 45-metre level. A reusable form divided into four parts, two per column, will be used to lay the concrete in the various modules of the main nave and transept.
STONE FOR THE ROOFTOPS, FROM SCOTLAND AND INDIA
As we explained in an article published on this blog earlier, there isn’t enough Montjuïc stone left, which is what was traditionally used to build the Temple. This is why we have opted for a combination of stones, from Scotland and Jodhpur Beige from India, to match the colours as closely as possible to the sections that have already been built.
Unlike the roofs on the side nave, the layout won’t be diagonal but in horizontal rows, like on the sections of the lower levels and the crossing that have already been executed. Moreover, the verticality of these walls makes it necessary to incorporate a mechanical fixing system to ensure the roof tiles don’t fall off over time.
The texture chosen for most of the stone blocks is slightly raised. The more complex elements, such as the windows, eaves and interior parts, will have a roughened texture to further emphasise their geometry.
Finally, the mosaic on the shields should be noted, which will be in different tones of white ceramic tile and some golden pieces in the same material as the pinnacles of the bell towers. The proposal will soon be validated with a prototype.
FLAT BRICK VAULTS TO SUPPORT THE ROOFS
To support the geometry of the roof, flat brick vaults have been designed that are interconnected by ceramic joists that coincide with the inflections between the planes of the roof and the paraboloids. Supporting this type of space with joists and vaults is a common resource in Gaudí’s work, which can also be seen at Casa Batlló and the Episcopal Palace of Astorga. In this regard, we also find examples from other works, such as Vapor Aymerich, Amat i Jover and Can Batlló, by architects Lluís Muncunill and Rafael Guastavino, respectively, which have clearly been references in understanding how to use flat brick vaults in our immediate area.
The joists are parabolic and built with bricks turned on the short side. They will be raised with the vaults to ensure they are a single, solid piece.
In planning the vaults, the general criteria proposed by Guastavino was used, with a deflection of 10% of the span. This creates an acceptable curve and ensures the vault works properly. The fact that it is curved means the edges of the vaults are thicker than the centre. This difference is filled in with light cement.
To build the vaults, we have turned to traditional Catalan vault-making processes, which use a grid framework to guide placement of the first layer of tile (single) in a herringbone layout. Between this and the second layer (double), the vault is reinforced with a Basalt fibre mesh to withstand winds and any possible seismic activity. On the roofs of the central nave, where the bending and axial forces will be greater than on the side nave the thickness of the tiles will vary to adapt to the structural needs and will also be reinforced with mesh on the outermost layer. In order to validate this solution, we’ve made a prototype of a section of vaulting at the warehouse in Galera.
Although the flat brick vault is a widely used technique, its performance depends on the materials used: the mortar and tile or brick. This is why we have done extensive trials to see how each of the materials proposed and the vault as a whole stand up.
THE LAMP OR VAULT KEYSTONE
The roofs, according to Puig Boada’s description, are “topped with aediculae that support the lamps.” This element has two functions. On the outside, the lamp represents the culmination of the Eucharistic discourse represented in the Temple naves. This is why each of the stone pieces will be covered in various tones of white ceramic tile, a symbol of purity, and the Tau, like that on the Nativity façade, in red tile, as a symbol of God. At night, this same role will be played by the light itself, which will create a subtle path of light uniting the three façades and the central towers, as a reference to the light of God.
Its other function is structural. The series of vaults used to create the roofs form a dome that requires a keystone to close the arch and generate enough weight to transfer the forces properly. The lamp, which weighs 37 tonnes and is 7 metres tall, will serve as this great keystone. It is pre-assembled with tendons uniting the individual blocks so it will act as a single piece.
So, construction of this part of the Temple is unique in that it is defined by large domes created from flat brick or stone vaults, built in the traditional manner on site, and crowned with a large, pre-assembled stone lamp.
Executing the work on the roofs of the central and side naves will cover the whole Temple and make it possible to see them, from inside and outside, fully completed for the first time.