Smiljan Radić uses an intricate tensile membrane construction to shelter the VIK Winery which nestles in the foothills of the Chilean Andes
Even in the benign climate of Millahue, 100 miles south-west of Santiago, roof design requires a disciplined approach, especially in the case of tensile membrane construction and even more so where the quality of building form, as well as performance, is top priority. On one level, architect Smiljan Radić’s VIK Winery is a work of art, like his coterminous 2014 Serpentine Pavilion. The way it relates to its heroic Sub-Andean context, through the controlled choice of forms and materials, is central to this artistic vision. But with its tensile membrane construction, the form of the winery’s roof could have undermined this order.
Specialist contractor Birdair, which developed and installed the winery’s roof, describes building membranes as equal stress fields that behave like soap film unless they are modified by structural members or air pressure. Horizontal membranes are especially problematic and difficult to achieve: large counteracting forces are needed to limit deflection under vertical load from water, snow and wind. Although early concept sketches suggest a more flamboyant roof form, with exposed triangular-section trusses, the VIK Winery is a very different animal from Hopkins Architects’ 1992 Schlumberger Cambridge Research Centre, with its expressive network of masts and suspension cables. In the case of the winery, it is the landscape which is heroic rather than the structure. With a span of 40m, the principal vat room space has an aspirational roof structure, but one which is understated and integrates with the ground plane.
Having a solar transmission factor of 12 per cent, the winery’s glass fibre and polytetrafluoroethylene membrane, or PTFE, composite roof fabric admits natural light to spaces below, where wines are fermented in stainless-steel tanks and visitors promenade through or on catwalks overhead. This has minimised the cost of artificial lighting for these spaces. It creates a stable, diffuse, ethereal, calming, though monotonous half-light reportedly good for winemaking. The roof comprises inner and outer skins spanning between the top and bottom members of lenticular trusses. Both are PTFE membranes, but the inner skin is lighter, with a different make-up of warp and fill reinforcement, lower breakage strength and trapezoidal tear resistance. Its flame spread and smoke generation parameters are also different from the upper membrane’s and, with its sound absorption factor of 0.7, it also has inherent acoustic benefits.
Birdair designed and executed the roof’s structure as well as its membranes. As in the design of glass walls, taking certain structural members out of the consultant engineer’s scope can improve coordination, simplify contractual interfaces, avoid disputes about what is and is not secondary steelwork and improve design quality, although architects are understandably wary of set menu style procurement where it is over-restrictive. Alongside the membranes, the roof trusses are integral to a holistic engineered strategy, where the structure and envelope complement each other. The simple linear boundary conditions and fabric mesh parameters were punched into form-finding software, using finite element analysis to size structural members.
Parallel and battered reinforced-concrete walls with fair-faced visible surfaces, bearing on raft foundations and in some cases used as retaining walls, were cast in situ. Then arrays of cruciform steel bearings were anchored to the tops of these walls, with fixings through their base plates. The painted carbon steel lenticular trusses were too long to be brought to the remote site as single elements, so they had to be assembled in situ before they were lowered onto the bearings. Circular hollow sections connect to the ends of these trusses, forming a continuous profile used to attach the membrane at the eaves. The trusses were then interconnected with diagonal CHS members, which brace the roof structure. This helps to avoid structural loading on the membrane.
Loose rolls of outer membrane were stretched over the top of the trusses and the corresponding inner lining was hoisted into place by pulling up steel cables at the eaves. All joints between these sheets are also PTFE. These connections were sealed using specialist irons at temperatures of 700 degrees F or more and heat-sensitive tape, forming durable permanent joints. Extruded aluminium profiles attached to the roof structure and fixed with stainless-steel fasteners were then used to connect and clamp the membrane panels. The inner membrane also serves to veil the trusses, along with their splice plates, fixings and the diagonal bracing.
At the ends of the vat room the membrane roof construction is reconfigured and cantilevered to form inviting and sheltering canopies, which also shade the curtain walls in these locations. These column-free glass walls open up views across the landscape from the depths of the vat room, as well as keeping out the elements and avoiding a wind tunnel effect. The vat room is not, however, a fully enclosed space. It has continuous unglazed clerestory slots below its projecting, gutterless, eaves. This avoids the clutter of openable window frames.
The winery is not a heavily serviced building, and it relies on the 73 per cent nominal solar reflectance of its PTFE outer membrane to avoid excessive overheating. The building’s external walls, substructure and landscaping also play a role in this passive environmental strategy which uses diurnal settings well suited to the processes it houses and the site climate. Most accommodation is below grade and this, along with its roof and concrete structure helps to regulate its internal climate. The inclined forecourt is a further enhancement. Here, water flowing below boulders of local granite and textured concrete paving helps to cool wine as it ages in barrels in the space below. This watery Ryōan-ji also negotiates the change in level as visitors descend to the level of the vat room mezzanine, helping the winery to sink into the landscape.
Visitors who complete the 130m procession through the squat nave of the vat room emerge in a level courtyard terminated by a pavilion used for wine tasting and sales. Preternaturally large clusters of replica grapes are suspended from its oversailing roof and, like the principal winery building, this is an architecture that forcefully projects itself horizontally into the space which surrounds it, like the best work of Mies, Wright, or Hadid, one of the many signature architects who have recently designed wineries. Early concept drawings suggest a hemispherical diagrid shell of a pavilion, but in the seven years from competition win to completion, the VIK Winery has evolved into something more rectilinear, and its holistic strategy and formal language echo the viticultural aspirations of its owner.
Architect: Smiljan Radić with Loreto Lyon
Structural engineer: Luis Soler P & Asociados
Tensile membrane contractor: Birdair
Photography: Cristobal Palma