Zaha Hadid Architects’ Serpentine Sackler Gallery combines the discipline of tensile fabric construction with formal invention, says Felix Mara. Photography by Luke Hayes
Those who found Sou Fujimoto’s Serpentine Gallery Pavilion a bit of a wash-out in July were offered a consoling Indian summer when its new permanent sibling opened in September. The new Serpentine Sackler Gallery completes a 13-year cycle. Its designer, Zaha Hadid Architects, was chosen for the original Serpentine Gallery’s first temporary pavilion commission in 2000. It’s unusual, not just as preternatural seafood at large in a Royal Park, but also as Zaha Hadid Architects’ first permanent inner-London structure and because, like MAXXI in Rome, it involved working with an existing historic building, a buff stock brick gunpowder store known as the Magazine, which was completed during the Napoleonic Wars. More unusual still, the new pavilion, which squelches up against this relic, is the practice’s first permanent tensile structure, so in some respects a new departure.
Working with conservation architect Liam O’Connor, Zaha Hadid Architects restored the Magazine lovingly but not over-zealously, seeing it as the yin counterpart to the yang tensile structure, as the practice’s phase 2 project lead, Fabian Hecker, explains. ‘The Magazine was conceptualised as a house within a house,’ he says. This involved constructing new roofs with glazed slots between the existing external walls and the central twinned barrel-vaulted gunpowder stores they gird, creating a circuit gallery space, like Leo von Klenze’s Neoclassical Glyptothek in Munich.
Some prefer the restrained Magazine to its voluptuous neighbour and may also be interested to know that it is now Grade II*-listed, although on an artistic and technical level it pales into insignificance as you enter the new pavilion, initially intended as a social space, but completed as a restaurant and bar and also seen by Zaha Hadid Architects as a vehicle for researching curvilinear structural surfaces. The practice’s portfolio bulges with convex volumes whose sub-components often work in compression. But at the Sackler, wanting to minimise the weight of materials, it decided to continue its experiments with tensile membrane construction. The anticlastic geometry which typifies this was potentially at odds with Zaha Hadid Architects’ sculptural, freeform vocabulary. Its saddle geometries and tent forms might fit more comfortably into Hopkins Architects’ oeuvre. As the practice wanted neither to abandon sculptural free-form geometry, nor to give up on tension membrane construction, the way forward seemed interesting.
‘We could have cheated and constructed a free-form external membrane on top of ribs spanning the 20m width of the pavilion,’ explains Arup project director Ed Clark. But this wouldn’t have been a bona fide anticlastic structural tension membrane. This involves a unique discipline, with fabric spanning between high points, which avoids flat surfaces that would be vulnerable to ponding. At the Sackler, these high points are provided by five inboard columns and a 21-tonne ring beam, between which the membrane spans, with tensioning rods at 300mm centres. The columns support the membrane and, symbiotically, the membrane restrains the column heads.
To add to the complexity, unlike many tension membranes this one also had to be Part L-compliant. So the roof comprises three independent layers: a high-performance PTFE-coated glass fibre woven textile external membrane about 2mm thick and designed for wind loads; an intermediate cable net supporting fire-rated mineral fibre multifoil insulation and third, a silicone-coated stretch fabric ceiling. The prefabricated internal and external membranes are tailored to the pavilion’s geometry and were laid on the ground before being jacked up, avoiding site welding.
The ring beam supporting the membranes is a ladder truss, which writhes like a roller coaster, beetling over the ground plane, with fixing zones for inner and outer membranes and anchored by base plates at three points.
The sense of freeform geometry, which reads more strongly internally, relies on the soft shapes of the moulded GRP overcladding to the ring beam and soffits, and of the columns, which taper and unfurl like lily flower flutes. These are fabricated from curved steel plates with horizontal and vertical stiffeners: 2.4 tonnes of boat hull construction each.
The project team took care to avoid distortion when their components were welded together and to ensure smooth site finishing. As further refinements, these columns frame lanterns where they meet the roof, ringed with light halos, and are lined internally with fibre-reinforced plastic. As Arup senior engineer Jolyon Smith observes, the lanterns’ angle and frit density are the outcome of form-finding. Arup added other clever enhancements, including a simultaneous heating and cooling GSHP, which until now has only been possible on larger projects and infrared smoke beam detectors in the gallery, inlieu of banal surface-mounted fittings. Unusually, these are only 100mm below the skylights.
As Zaha Hadid Architects partner Patrik Schumacher explains, parametric modelling has enormous potential for passive environmental design. Nevertheless, the roof cantilevers proposed for optimum shading at the Sackler were tamed. The perimeter glazing, however, cantilevers vertically to avoid spanning onto a roof structure subject to some deflection. Curved glazing meets the roof soffits abruptly and here the geometry seems overwrought. Their low-iron spec is also a luxury in such a green setting, but it’s a refinement which can be offset against savings on steelwork made possible by the tension structure. The Serpentine Sackler Gallery’s soft forms belie its iron design logic and tectonic discipline.