Kengo Kuma uses the precision of precast concrete to conjure the spirit of the Middle Ages
Japanese architect Kengo Kuma has added a precast-concrete portico to the western entrance of Angers Cathedral in northwest France. The 21m-long structure serves as a gallery as well as a protective canopy for the sculptures that adorn the 13th-century edifice.
Kuma’s design was selected in 2021 from a competition with five entrants, and the studio said its goal was to “put ourselves in the shoes of the builders of the Middle Ages”.
The new portico comprises five Roman arches based on the geometric proportions of the medieval facade. The underside of each element, or archivolt, steps down in a staggered pattern of ever-decreasing arches. The freestanding structure does not touch the cathedral at all. Instead, it is supported on eight mini piles, which are as slender as possible so as not to encroach on the historic foundations.
Precast concrete was chosen because of the precision required for the moulded detailing, and to reduce the impact of construction work on the heritage environment. The precasters modelled the component parts in 3D before crafting the timber moulds.
The concrete itself was specially developed for the project and was based on the various shades of limestone found on the cathedral facade. The aggregates range in colour from ochre to light brown, and were locally sourced from the Blois area of the Loire basin. The sand used in the concrete was also from the Loire.
The roof slabs have the same tone but use a different mix of fibre-reinforced ultra-high performance concrete – reflecting the fact that the structure has a design life of 100 years.
The portico was initially cast in 600 separate pieces, which made it easier to apply the polished finish to the triangular profile of the archivolts. These were then assembled in the factory into three larger components: the vertical walls, arches and roof. Finally, they were delivered by truck through the narrow medieval streets of Angers to the cathedral for final positioning.