The Alta Tower by Hamonic + Masson is not the sort of new building you would expect to find in the heart of a Unesco World Heritage site.
With its spiralling, asymmetrical form and gleaming balconies of glass and pale precast concrete, the residential tower neither fades into the background nor fits inconspicuously into its historically significant context.
But then, this is not a typical Unesco site. Alta occupies a prominent location in the grid-like masterplan of Le Havre, the concrete city designed by Auguste Perret – the Parisian architect who pioneered the use of reinforced concrete in architecture – and which rose from the rubble of the northern French industrial port in the two decades following the Second World War.
The 60m-high Alta stands on a key junction in the ordered, classically proportioned streets – one originally earmarked by Perret for a tower – and within nodding distance of the other celebrated addition to the post-war plan: Oscar Niemeyer’s curvaceous Volcan cultural centre, which was completed in 1982. The challenge for Hamonic + Masson, which won the competition for the project in 2015, was to find an architectural language in keeping with these “two sacred monsters”, as the practice puts it.
The twisted geometry of Alta is their response. A matrix of inclined precast concrete columns and 400mm-deep balcony edge beams reflects “the grid and order of Perret”, whose buildings were founded on an expressed structure of repeating 6.4m-long units. But as the tower rises, it appears to turn through more than 90 degrees, as if it is looking over its shoulder. This adds a curve to the silhouette that echoes “the form and sensuality of Niemeyer”.
The complex form required an iterative design process between the architects and structural engineer Legendre, facilitated through the use of a shared BIM model. The structure is based around a 6m x 6m in-situ concrete core, which carries the 230mm-deep floor slabs to the loadbearing envelope. Behind the perception of a spiral lies a more coherent structural form, “like a truncated pyramid, solidly superimposing smaller floors onto larger ones,” explains Jean-Christophe Masson, co-founder of Hamonic + Masson.
The twist is accentuated through the design of the projecting balconies, which vary in width from 1.5m to 3.5m in the corners. To create these large overhangs the slabs were post-tensioned, with the unbonded tendons running from each corner of the 300mm-thick balcony slab towards the core. The contractor had to make bespoke balcony tables for the formwork, as well as developing multi-level cantilever shoring methods. This again harks back through Le Havre’s concrete history: post-tensioning was first used in 1933 on the Le Havre Marine Station project by Eugene Freyssinet (and the modern-day company bearing his name engineered the post-tensioned solution on Alta).
The precast external columns measure 300mm x 400mm in plan but are all unique in their angle and positioning. “An innovative formwork process was implemented to promote the reuse of moulds while producing different columns each time,” explains Masson. “The placing and anchoring of these columns was a significant area of focus, with the structural engineering team and our own project manager overseeing the installation of each inclined post.”
Precast concrete was specified by the architects both to give a precise, smooth appearance and to pay homage to the innovative construction techniques used by Perret’s workshop. Local cements and a stained finish combine to create a light-coloured concrete “that interacts with Perret’s architectural style and engages with the city’s unique light”.
Perret’s adoption of prefabricated elements was partly in response to the need to rebuild quickly after the war. But it also reflected a desire to improve living standards. The 6.4m dimensions of his structural units were derived from his determination to provide 6m x 6m living spaces, while incorporating 1.5m-high windows on every facade.
Hamonic + Masson was anxious that Alta express similar values. The concentration of structure around the perimeter has freed up the floorplates for open, flexible layouts, all with large corner windows. But where Perret offered uniformity, Alta proposes individuality: the 64 apartments across 16 floors have a variety of configurations and the column-free interiors allow residents to customise layouts and even join apartments together to make larger properties.
This freedom and flexibility should endear the building to its residents over the long term – and perhaps one day make Alta a new sacred monster on Le Havre’s skyline.