The Fifth Desk · Evaluation
Act I · The Map
Félix Candela · a restaurant under one thin shell, scored as the shell as it stands and the building it makes: the vault, its eight supports, the room it covers and the enclosure and use beneath it as they now are · a reinforced-concrete thin shell, a groined vault of four hyperbolic paraboloids intersecting on a vertical axis, giving eight segments about one centre on an octagonal plan, each a ruled surface formed on straight timber boards · the vault brought down at eight points, where the groins between the segments meet the ground, thickened there into V-section ribs; the outer edge of each segment cut obliquely to the surface, so that every lobe ends in a free, upturned edge rising to a point, with no edge beam · on the canal bank at Xochimilco, Mexico City · completed 1958 · Félix Candela, as designer and builder, through his firm Cubiertas Ala · as it stands, the shell as built, the glazing and fittings of the room beneath it altered since
Mode
A restaurant roofed by one structure; a demonstration of the thin shell made the figure of a place of pleasure
Mythos
The canopy held over a gathering; the centred figure of eight, a mandala in plan; the flower on the water in the place of flower fields
Phase
Completed 1958, at the summit of Candela’s work with the hyperbolic paraboloid begun in 1951; the canonical case of his shells since; its enclosure and fittings altered since, to an extent not established
Presentation
Four intersecting hypars giving eight segments on an octagonal plan; eight groins thickened into ribs at eight supports; free edges cut obliquely, with no edge beam; a glazed room beneath
Register
Buoyant, graceful and lyric; festivity and shade over water; delight rather than awe
Scale
One room under one roof; a meal by the water, a canal bank, the light on concrete
Governing Proposition
Eight lobes of concrete lift their points above a canal bank at Xochimilco, and the vault between them comes down to the ground at eight points only, over a room for eating open on every side. The wager of the building is that concrete, the material of mass, can be made to stand as a membrane a few centimetres thick when the form and not the material carries the load; that a surface chosen because carpenters could build it on straight boards can be the figure of the whole; and that a place of everyday pleasure can be given a roof as considered as a church’s.
Act II · The Essay
Movement I
The restaurant at Xochimilco, in Mexico City, was completed in 1958. Its shell was designed and built by Félix Candela through his own firm, Cubiertas Ala, which built what it designed. The shell is Candela’s by every account, and whatever share others had in the restaurant is not charged against it or credited to it. Because the firm built as well as designed, the stake was Candela’s twice over: if the shell had failed, the failure would have been his as engineer and as contractor. That is the first fact of the building, and it governs the rest. The form was chosen by a man who had also to make it stand.
Candela had been building with the hyperbolic paraboloid since 1951: a pavilion at the university, the umbrella roofs of warehouses, a church. Behind him stood the thin concrete shells of Torroja and Freyssinet and the German barrel vaults, and behind them the old groined vault of masonry, where two vaults cross and the load runs down the valley between them. The thin shell answered a particular economy. Where steel was costly and skilled labour cheap, a roof could cover much with very little material if enough care went into the form and the formwork. In Mexico in the 1950s that economy held, and Candela’s roofs were built in it.
By 1958 the hypar and the groined form were his and proved, and the shell at Xochimilco is the summit of that path more than a turn off it. What is new is the combination and the figure: a radial groined vault of intersecting hypars with every edge cut free and no edge beam anywhere, so that the efficient roof of a factory becomes a figure lifting off the ground. It was built at a thinness the theory of the day did not comfortably cover. Candela worked by membrane theory and his own judgement more than by full analysis. Mexican modernism of the time was otherwise mural and massive; this roof was neither.
Movement II
The geometry is simple to state. A hyperbolic paraboloid is a saddle, curved two ways at once, and it is doubly ruled: through every point on it run two straight lines that lie wholly in the surface. Four such saddles are set to intersect on a vertical axis. Where they cross they cut one another into eight segments about one centre, on an octagonal plan, and the lines along which neighbouring segments meet are the groins, the valleys of the vault. The whole roof is one surface type repeated eight times round a point, and every part of it, from the crown at the centre to the tip of each lobe, belongs to the same four saddles.
The surface was chosen because it could be built. Being ruled, each segment could be formed on straight timber boards, laid side by side so that together they made a curve. The carpenters did not have to shape anything curved; they had to set straight boards in the right order. The means of building was chosen together with the form, and the labour that made the roof is written into its geometry: the ruled surface is the record of a formwork that skilled hands could raise cheaply and quickly. That economy, more than any doctrine, is what made the shell possible, and the shell shows it in every line of its underside.
The shell is a few centimetres thick across the whole room, in proportion thinner than an eggshell. It stands because the form and not the material carries the load. The load is gathered into the groins, and the groins are thickened just where the stress requires, into V-section ribs that come down to the ground at eight points. Take one segment away and the vault is no longer in equilibrium; take away the ribs and the load has nowhere to go; thicken the shell and the form loses the point of itself. Little in architecture resists the subtractive test so nearly absolutely.
Movement III
The decisive cut is at the edges. The outer edge of each segment is cut obliquely to the hypar, so that each lobe ends in a free, upturned edge rising to a point. There is no edge beam anywhere. A shell is usually stiffened at its border, where the surface ends and has nothing to lean on; here the border is left as thin as the rest, and the oblique cut is what lets it stand. It is the hardest decision in the building and the most beautiful, and the building’s beauty and its structure depend on it together. Modern re-analysis by computational methods still asks how near those edges come to their limits.
From outside the effect is of weight that should not be possible. The eight points lift off the ground and the water like petals, or the hem of a skirt caught by wind, and the whole vault seems to rest on the ground at a few points only. The eye runs down each groin to its support and up each edge to its point, and finds the same surface doing both. The two most distant elements of the building, the lifted point of a lobe in the light and the groin rib meeting the ground in shadow, are the thinnest edge and the thickest part, and they obey one law: one ruled surface read from its free edge to its valley.
Few buildings are as single in law. Every line of formwork, every curve of edge and every rib follows from the four saddles, and the eight lobes are one law repeated round a point. The narrowness of that law is also its limit. The range is one surface, one material, one gesture, and narrowness is not coherence. Below the shell a second and plainer law takes over. The enclosure and the restaurant’s fitting, the glass walls and service spaces, are set under the vault and not generated by it. The craft of the building is the shell’s more than the room’s, and the room is ordinary where the shell is not.
Movement IV
Xochimilco is, by its Nahuatl name, the place of flower fields: a district of canals and chinampas, the cultivated plots its farmers have worked for centuries. The canals and the chinampas are the building’s setting, not part of it. The restaurant stands at the water among the flower gardens, opening on all sides, and the site compels part of its form: a room for eating by the water wants to be open, and the shell, bearing at eight points only, leaves every side free. The eight lobes stand on the canal bank as a flower on water. The form constructs that image rather than decorating itself with it; the lotus and the shell often seen in it are allusions only.
Inside, the vault floats over the room and rises toward the glazed edges, so that light enters where the roof is highest and the ceiling descends toward the middle. It is a dome inverted: where a dome is darkest at its rim and lightest at its crown, this roof is lowest at its centre, over the diners, and opens at its edges to the sky and the water. In plan the eight segments radiate from that low crown, a mandala whose centre is the table. The groins draw the eye down to the eight supports. The elevation recurs at every hour, with the light on the concrete and on the water, and it is of one kind: buoyant, graceful, lyric.
Put the room under a flat slab on columns and almost everything it gives is lost: the rising edges, the light from where the roof is highest, the openness on every side with no wall bearing, the sense of dining under a canopy that hardly touches the ground. The form makes a meal an occasion, and makes the structure the thing the visitor comes to see. It does not make the restaurant. Kitchen and service are indifferent to the vault and fitted in under it. The building’s fainter truth lies there: a place of everyday pleasure in a working district, given a roof as considered as a church’s, in a country where labour was cheap and steel costly.
Movement V
The shell made Candela’s name worldwide and became a fixed point in teaching and in the history of structure. Hypar roofs spread widely in the late 1950s and 1960s, many of them lesser, and the expressive concrete shell of those years grew in a climate it helped make. The TWA Flight Center (8.0), of the same moment, is the nearest building on the desk: its shells are sculpted to a figure, where here the structure is the figure. The Sydney Opera House (8.6), which took Candela’s shells into its inheritance, took the larger stake and reached much further. The Cathedral of Brasília (8.4), a Latin American concrete work of the period, holds far more of disclosure and archetype than a restaurant can.
The line the shell crowned was cut short. Within a decade shell building waned, on the cost of formwork and labour, and the economy that had made the ruled surface cheap to build was gone. The later revival of free-form roofs owes it homage more than method. Candela himself returned to the form late, in a restaurant at Valencia. Engineers and historians have returned to it steadily: in monographs and exhibitions on Candela, in the literature on structural art and on shells, in re-analysis of how so thin a shell stands, and in the history of shell building’s decline. The questions are mainly how it stands, and once the geometry is grasped the form is lucid.
What stands is the shell as built: the vault and its eight points, legible and unaltered in their governing idea, sixty-eight years after completion, outliving the economy that produced them and reading as no period piece. The room beneath has changed. Its glazing, enclosure and fittings have been altered, how often and how far is not established here, and the present condition of the concrete is not established either. Neither change touches the law of the roof. The building holds the water, the gardens and the light, the pleasure of eating together, the place and, faintly, the labour written into its boards; the state, the sacred, the family and history beyond the name of the place lie outside it. It is a single room under a single roof for a single pleasure, and the roof is complete.
Act III · The Twelve
Judged on structure, purpose and site. The shell resists the subtractive test almost absolutely. Remove a segment and the vault is no longer in equilibrium; remove the groin ribs and the load has nowhere to go; thicken the shell and the form loses the point of itself. Even the oblique cut of the edges is required, for it is what lets each edge stand free without a beam, and the eight identical segments are the logic of the intersecting hypars, not repetition for ornament. The site compels part of the rest: a restaurant at the water among flower gardens, opening on all sides. What yields is the purpose. The room needs a roof, not this vault, and kitchen, service and enclosure are fitted in rather than generated. The structure is compelled; the restaurant is permitted.
Score: 8.4 / 10
What can be stated, and holds: concrete, the material of mass, can be made to behave as a membrane over a whole room when the form and not the material carries the load. The building shows it to anyone who stands under it and sees the edges against the sky. A second truth is fainter: a place of everyday pleasure in a working garden district can be given a roof as considered as a church’s, a disclosure about who receives architecture in a country where labour was cheap and steel costly. What holds the axis: the first is a disclosure of structure more than of a human or social condition, which ranks below an articulated human truth, and much of what the building gives is mood, lightness, festivity and shade over water.
Score: 7.5 / 10
Elevation is high and frequent, and of one kind. From outside, the eight points lift off the ground and the water like petals or a hem caught by wind, and the whole seems to rest on a few points only, a weight that should not be possible. From inside, the vault floats over the room and rises toward the glazed edges, so that light enters where the roof is highest while the ceiling descends toward the middle: a dome inverted. The groins draw the eye down to the eight supports. It recurs at every hour, with the light on the concrete and on the water. What holds the axis is register: buoyant and graceful, never awful; the room is small enough that grandeur yields to delight, and the height is lyric, not tragic or vast.
Score: 8.4 / 10
Built into plan and section: the canopy held over a gathering, the tent or umbrella of shade, and the centred figure of eight radiating from one point, a mandala in plan whose centre is the low crown over the diners. The flower on the water is close to built rather than read in. Xochimilco is, by its Nahuatl name, the place of flower fields, and the eight lobes stand on the canal bank as a flower on water, which the form constructs rather than decorates. The popular images of a lotus or a shell are allusion and are not credited. What holds the axis well below the gate: the archetype governs the roof, not a procession, threshold or rite. Nothing in entering or using the room enacts it, and a restaurant asks little of it.
Score: 7.7 / 10
The inheritance: the thin concrete shells of Torroja and Freyssinet and the German barrel vaults; Candela’s own hyperbolic paraboloids from 1951, in a pavilion at the university, the umbrella roofs of warehouses and a church; and the old groined vault of masonry. The departure: a radial groined vault of intersecting hypars with every edge cut free and no edge beam anywhere, the efficient roof of a factory turned into a figure lifting off the ground, at a thinness the theory of the day did not comfortably cover. Candela worked by membrane theory and his own judgement more than by full analysis, and the stake was his as builder as well as designer. What holds the axis: the hypar and the groined form were already his and already proved; this is the summit of a path more than a turn off it.
Score: 8.4 / 10
Put the restaurant under a flat slab on columns and see what is lost: the rising edges, the light entering where the roof is highest, the openness to water and sky on every side with no wall bearing, the sense of dining under a canopy that hardly touches the ground. The form makes a meal an occasion under a lifted roof by the water, and makes the structure itself the thing the visitor comes to see. That is the form’s doing. What holds the axis: the form serves the purpose in mood and openness only. The workings of a restaurant, its kitchen and service, are indifferent to the vault, and the enclosures and fittings set under it, altered to an extent not established, temper the openness the form proposes. The form serves the structure’s knowledge more than the use’s.
Score: 8.3 / 10
Evidence over promise, across sixty-eight years. Engineers and historians have returned to the shell steadily: as the canonical case of Candela’s hypars in the literature on structural art and on shells; in monographs and exhibitions on Candela; in re-analysis by modern computational methods, asking how a shell so thin stands and how near its free edges come to their limits; and in the history of shell building’s decline after the 1960s as labour costs rose. Candela himself answered the form late, in a restaurant at Valencia. What holds the axis: the questions are mainly structural and historical. Once the geometry is grasped the form is lucid rather than inexhaustible; it yields understanding of how more than of what it means, and the restaurant as a place has drawn little reading.
Score: 7.9 / 10
Field: the thin shell in twentieth-century building, and modern architecture in Mexico and Latin America. The intrinsic force is high: the clearest demonstration of what the hyperbolic paraboloid could do as figure, and of the free edge as a structural and expressive means, reorganising what a concrete roof could look like when Mexican modernism was otherwise mural and massive. Achieved reach is scored with intrinsic force: real but bounded. It is a fixed point in teaching and in the history of structure; it made Candela’s name worldwide; hypar roofs spread widely in the late 1950s and 1960s, many lesser; and the expressive shell of Sydney and of Saarinen grew in a climate it helped make. But shell building waned within a decade on the cost of formwork and labour, and the later free-form roof owes it homage more than method.
Score: 8.3 / 10
Weighed on form, use and fabric together. The form survives whole: the vault and its eight points as built, legible and unaltered in its governing idea. It has outlived the economy of cheap skilled formwork labour that produced it, does not read as a period piece, and after sixty-eight years remains the case the literature on shells turns to. Use and fabric are weighed with less certainty. The enclosure and interior beneath the shell have been changed, how often and how far is not established, and the present condition of the concrete is not established either; the figure carries that uncertainty and is held a little below the usual step for its age. Presence is wide among architects and engineers and narrower among the public, and earns little. What holds the axis is what cannot be shown of the fabric, not what is known of the form.
Score: 8.7 / 10
Judged as command of building, structure and engineering included. The making is load-bearing in the strictest sense. The geometry was chosen so that the surface is ruled and could be formed on straight timber boards: the means of building chosen together with the form. The shell is a few centimetres thick across the whole room, in proportion thinner than an eggshell; the load is gathered into the groins, thickened just where the stress requires; and the free edges, cut obliquely to the surface, stand without beams, at once the hardest decision and the most beautiful. Few buildings anywhere carry their making so completely. The costs: the enclosure, glazing and fitting of the room are ordinary and later altered, and the craft is the shell’s more than the building’s.
Score: 9.0 / 10
Take the two most distant elements: the lifted outer point of a lobe in the light, and the groin rib meeting the ground in shadow. One is the thinnest edge and the other the thickest part; one rises and the other descends. They obey one law: the same four hypars, one ruled surface read from its free edge to its valley, so that the eight lobes are one law repeated round a point, and every line of formwork, every curve of edge and every rib follows from it. Few buildings are as single in law. What holds the axis: narrowness is not coherence, and the range is narrow, one surface, one material, one gesture; and beneath the shell the enclosure and service obey a second and plainer law, set under the vault and not generated by it.
Score: 8.3 / 10
The orders held: the natural order, in the water, the gardens and the light on the vault; structure and material as an order of their own, the law of the membrane made visible; the social pleasure of eating and gathering; place and memory, faintly, in a vault set as a flower in a district named for flowers and worked by its chinampa farmers for centuries; and labour, faintly, in a form made possible by cheap skilled formwork and written into its ruled surfaces. They are held in one structure but lightly, present more than integrated. What holds the axis lowest is what is absent: the state, the sacred, the family, history beyond the name of the place, and individual consciousness. A single room under a single roof for a single pleasure: the figure describes the form.
Score: 6.3 / 10
Act IV · The Reckoning
8.1 / 10 · Final Average
Placement: Tier IV · Canonical
Strongest Dimensions
The Made at 9.0, then The Imperishable at 8.7. A shell a few centimetres thick, its surface chosen so that it could be formed on straight boards, its load gathered into thickened groins and its free edges cut obliquely to stand without beams, the making load-bearing in the strictest sense; and a form that survives whole and unaltered in its governing idea, outliving the economy that built it. Behind them stand The Inevitable, The Sublime and The Swerve at 8.4: a structure that resists the subtractive test almost absolutely, an elevation renewed at every hour, and the summit of a path of shell building carried to a figure with every edge cut free.
Limiting Dimension
The Encompassed at 6.3, then The Unconcealment at 7.5. The building holds the water and the light, the order of structure, the pleasure of a meal and, faintly, place and labour, while the state, the sacred, the family, history and individual consciousness stay outside; and what it discloses is chiefly a truth of structure, concrete made a membrane, with a fainter truth about who receives architecture, and much of the rest is mood. Then The Archetypal Deep at 7.7 and The Bottomless Well at 7.9: the canopy and the flower on the water govern the roof but no rite of entry or use, and once the geometry is grasped the questions it raises are of how more than of what. The facts are one: a roof complete in its law, over a room that asks little of it.
The Necessity Cap clears at 8.4 against a threshold of 7.5. The Coherence Floor clears with room: The Made at 9.0, The Living Form at 8.3, The Inner Law at 8.3, each against 7.0. The Epochal Gate is unmet: The Imperishable at 8.7 clears the bar of 8.5, but The Swerve at 8.4 falls a tenth short, Pressure on Tradition at 8.3 two tenths short, The Archetypal Deep at 7.7 eight tenths short and The Unconcealment at 7.5 a full point short. The Universal Minimum is met: The Unconcealment at 7.5 meets it exactly, and no other axis but The Encompassed falls below 7.7. The Encompassed, which it exempts, clears its own floor of 6.0 at 6.3. Four of the five summit conditions are met. The work stands where its aggregate places it: 8.1, from a sum of 97.2, in the lower part of the band of Tier IV, short of the 9.0 that the summit requires.
Basis · a reading from knowledge of the building and its documented structure. No plan, image or written source was consulted. The work scored is the restaurant shell at Xochimilco as it stands, completed in 1958, scored as the building it makes: the vault, its eight supports, the room it covers and the enclosure and use beneath it as they now are. The canals and chinampas of Xochimilco are setting and are not scored. The shell is credited to Félix Candela, who designed and built it through his firm Cubiertas Ala; others who shared in the restaurant are not named here, and collaboration is not charged. The glazing, enclosure and fittings of the room beneath the shell have been altered since it was built; how often and how far is not established, and the change is weighed under The Imperishable and The Living Form only. Nothing is quoted. Facts that could not be verified, among them the patrons and any architect credited beside Candela, the exact thickness of the shell, its span and the heights of its points and crown, how the thrusts of the groins are taken in the soft ground of the old lakebed, the building’s record through later earthquakes and any repair, the continuity of its use, the dates and extent of the alterations, and the present condition of the concrete, are not given.