La Sagrada Família: a collaboration in digital and stone

We modelled each and every component in 3D to a construction level of detail (including nuts, bar threads, couplers, fillets and chamfers). Carefully designed and constructed connections ensure that when panels are craned into place, they fit together accurately like Lego blocks, without further adjustment. 

Our prestressed stone panel method echoes the pure masonry construction used in the earlier construction of the Sagrada, while the more modern off-site manufacture approach has guaranteed consistently high quality and fast assembly. Over 870 panels weighing up the weight of two London double-decker buses have been constructed and installed on site. On average, they were installed in under 30mins, saving time and enabling a safer construction process – important as the basilica has needed to remain open during the final years of the build.

The Jesus Cross – Gaudi’s crowning achievement

At the centre of the temple is the largest tower dedicated to Jesus Christ. Rising highest of the eighteen towers and culminating in a monumental four-armed cross, clad with hand-made glazed ceramic tiles, the recent completion of this tower makes the Sagrada Família the tallest church in the world. The structure of the Jesus Cross is a self-supporting monocoque shell, combining slender ribs of duplex stainless steel with a thin skin of ultra-high-performance concrete to create a structural system of extraordinary lightness, performance and durability.

A structural engineering puzzle for the ages

The Jesus Cross is a truly monumental construction. Standing 17m (about 5 storeys) tall above the top of the Jesus Tower  and spreading 13.5m wide at the arms, it would be an imposing presence even at ground level.

During his lifetime, Gaudí defined the Jesus Cross in both form and function. He described its impression as ‘brilliant’, with glazed tiles scattering light from its surface like crystal. A spiral staircase allows visitors to ascend into the onyx lined interior of the cross itself, and look down through windows to the city of Barcelona below. The outer surface is defined by ruled surfaces – hyperbolic paraboloids and helicoids – which can be described in pure mathematics using a series of straight lines.

With the shape, materiality and function of the cross defined, the design team turned their hand to the technical challenges, chief of which was space. Just twenty centimetres, roughly a hand’s breadth, separate the outer surface from the space for visitors inside.

Within this zone, the cross needs insulation to ward off the summer heat and a supporting structure, strong enough to protect the brittle tiles and glass from extremes of wind and temperature, and even a potential earthquake, and a beautiful internal lining.

An efficient and elegant solution

Typical structural solutions quickly proved to be unsuitable.

To make best use of the space and materials, the Jesus Cross brings the structural frame and outer skin together into a single structural shell – a monocoque. The ultra-high-performance fibre-reinforced concrete gives the structure form and stiffness, supporting the tiled outer surface and keeping the elements at bay, while a web of high strength duplex stainless steel ribs strengthen the frame and control cracking. No material or space is wasted, creating a composite shell that is both thin and robust. The tiles on the outer skin, and their supporting steel frame, trace the lines of the parabolic surface, weaving Gaudí’s vision once again into every part of his masterpiece.

Validating the design

Having created the new composite shell system, the Jesus Cross team needed to verify and develop the design in detail. Working from fundamental physical principles the team derived a new theoretical model for how the combination of materials would behave, testing and refining our ideas to predict the structure’s behaviour under each potential scenario.

For this unique system, engineering design must go beyond theoretical models. The team carried out full-scale testing on a collection of sample panels, designed to replicate the most important effects they had predicted on paper. The samples were tested to destruction, proving the strength, stiffness and robustness of the system that they had assumed.

The 2026 completion of the Jesus Cross was made possible by the combined efforts of the whole design and construction team, whose inventive combination of architectural vision, physical theory, cutting-edge analysis and practical mock-up testing, are rooted the best traditions of the basilica’s long history.

Human, digital, physical 

In all our work on the Sagrada Família we have used the latest digital tools to produce workable structural designs. This parametric design approach combines deep human knowledge of the structural variables in the Towers’ form and position, with powerful algorithmic tools that could model the hundreds of subtle variations of geometries for the design. This human-plus-digital ethos was the best way to make Gaudí’s inspirational design pragmatic to construct in a realistic timeframe, and would have been unrealistically laborious to carry out without cutting-edge technology.

Our experience working alongside 2BMFG Architects and the Sagrada Família Foundation has demonstrated how the near-limitless capacity of digital tools, used creatively by human beings with their experience and insight, can solve almost any engineering and construction challenge – even on projects as singular as Gaudí’s remarkable church. 

Spiritual building, human collaboration

The topping out of the Sagrada Família in February 2026, after over a century of endeavour, embodies the true potential of human ambition and collaboration.

At Arup, we’ve always held to our founder’s conviction that truly excellent and enduring work in design and engineering can only be achieved by teams who commit to developing a ‘whole’ solution that is greater than the sum of its parts. To be able to come together with inspiring collaborators, around a shared vision, and to approach each challenge with both bravery and humility, is the surest way to achieve success and realise a vision as ambitious as Gaudí’s.

Our approach to, and experience of, delivery on the Sagrada project has demonstrated this total design ethos at every stage – it’s been an incredibly rewarding joint effort by the client team, their architects, their builders, our and other engineers, specialist subcontractors, local stone masons and other craftspeople, digital innovators, materials experts, historians, city leaders and countless others.  

Images and video © Fundació Junta Constructora del Temple Expiatori de la Sagrada Família