Technical and architectural history of the minimalist window

The reduction of the frame from sliding to mere edge (by the possibility of using glass as a structural element) is actually an extremely simple idea. This technical, formal choice was synthesised, very effectively, by the Swiss architect Andrea Bassi and the entrepreneur Eric Joray, who launched the Vitrocsa trade name in Saint-Aubin en Sauges (Switzerland) in 1992. However, knowing that the development of a product is a time-consuming technical process – as we discussed in the previous chapter – may help explain the gap between the launch of minimalist frames and their commercial success. Indeed, the Vitrocsa “3001” series had to wait more than a decade for companies from different countries to show any interest in marketing the system following its presentation at the “Intérieur” Design Fair in Kortrijk (Belgium). The product was of disarming simplicity and elegance and included a series of truly revolutionary elements: a modular roller bearing track that allowed better performance than any previous solution and very easy maintenance and replacement; the extremely slender and sturdy bolt latches; and a structural bonding system that ensures that glass and aluminium are perfectly solidary and geometrically accurate. In addition, the vertical profiles were slimmer than any other system thus far (18 mm thick), which has made it a landmark in sliding frame systems.

In 2003, Jofebar introduced the product in Portugal. Its first application was in the houses of two Jofebar shareholders, the emblematic Houses in Ponte de Lima, designed by Eduardo Souto de Moura. Shortly afterwards, in the Braga Stadium, minimalist windows and doors are again used, associating the product with Souto de Moura’s architecture. The widespread international dissemination of these projects along with other large-scale buildings, such as residential towers and real estate developments with hundreds of houses, form the outline of a market that had never existed for this type of frame. In 2005, Jofebar launched the product in Spain and, two years later, in the United Kingdom and the United States of America, where it supplied and installed Goldbrecht’s first projects (currently Vitrocsa’s US distributor). The market grew very rapidly and, in the ensuing years, reached an unparalleled success, with Jofebar becoming Vitrocsa’s main client, transforming and installing much of its production.

Although the product was technically innovative and operated with sliding panes up to 6m², allowing seamless floor, ceiling and walls integration (which ensures total transparency between the interior and exterior), it was still a compromise solution when it came to watertightness and thermal and acoustic insulation. This was a technical limitation that was hardly compatible with the extremely demanding Swiss market but has found, in the more temperate climate of Portugal and Spain, an environment suitable for the rapid and exponential success of the product.

High-performance glass was now easily available and as of 2007 it was clear that the market for minimalist windows required a much larger industrial capacity so to meet demand. It was imperative that minimalist windows would keep pace with this improvement in glass performance and could overcome their deficiencies, of water leakage, air permeability and energy efficiency.

Other competing companies start to gain ground and build a truly industrial project, the most important one being the Swiss Sky-Frame, and the system is subject to improvement and progressively overcomes its initial limitations, becoming technically more efficient, economically more competitive and more varied in the range offered. This unfolding of events has led Jofebar, without the support of its Swiss counterpart, to forcefully focus on the development of custom-made solutions, almost tailor-made, that allowed them to bridge clear performance gaps. This would eventually lead both companies to progressively move apart from each other.

Taking advantage of its metalwork experience and know-how in doors and windows, Jofebar has continually risked pushing the possibilities of the materials to the limit and simultaneously developing its products in tandem with the creative designs of the architects and each project’s specificities. Very early on, it began the task of adapting the system, being particularly interested in replacing glass with other materials and transforming the system in a process for moving any structural element. As early as 2005, therefore, the profiles of minimalist frames were accommodating different types of shutters in non-scalable solutions, since they were detailed specifically for certain projects. This is the case of the wooden shutters of Rocaford House (Valencia, Spain), to the design of Ramón Esteve, and the geometric meshes with irregular motifs, initially designed by the Israeli designer Itamar Burstein, which served as a basis for applications in various works. In the following year, Jofebar took part in a project which, although not completed, became emblematic for the company: the residential and tourist complex of Porto Senso in Altea (Spain), designed by Jean Nouvel with Ribas & Ribas. The first test with a hidden bottom track has been developed for this project, and built into a system of sliding shutters in a metal structure with stone gabions. This project paved the way for the development of solutions where the sill was invisible – a kind of execution detail long tried by different architects, such as the sliding walls of Alvar Aalto’s Imatra Church (Finland, 1958) and the Capela das Aparições in Fátima (Portugal, 1982) by José Carlos Loureiro. The motorisation of window frames was also developed, in sliding prototypes for Casa Fez (Porto, Portugal, 2006), by Álvaro Leite Siza, and the first large sash window in the House on Bassett Road (London, United Kingdom), by Paul+O Architects, completed in 2008. Note that the first use of minimalistic window frames with a sash opening – without motorisation – had been launched shortly before, with the Vitrocsa sash series, used in the Edifício Transparente (Porto, Portugal, 2006), renovated by Carlos Prata.

It is only in the post-2008 economic recovery that minimalist windows had become a mainstream product and other players like Keller Minimal Windows (1)1.  A former Vitrocsa partner, Keller AG established Keller Minimal Windows in 2007 and filed for bankruptcy in 2020. Info: Luxemburger Wort. have appeared, and that established multinationals such as Schüco, Sapa and Reynaers got genuinely interested in the technology. For Jofebar, the focus on larger glasses was a lever to improve the system. The sliding window frames of Casa do Bom Jesus (Braga, Portugal, 2009), by Topos Atelier, were the first to achieve large-scale glass panes in a vertical layout (2.20 x 5m). Prior to this, a first solution with a double parallel bearing bottom track was developed for the Archaeological Museum of Côa (Portugal, 2007), a design by Camilo Rebelo and Tiago Pimentel. It allowed for glass dimensions up to 15m², much greater than those then allowed by the rival minimal frame systems, but with glass panels arranged horizontally. In addition, a first “pocket” solution with a balustrade was developed specifically for this work – whereby the window retracts into the wall and gives way to a glass balustrade. It was this project, moreover, and the prototypes developed for it that gave rise to the further development of the panoramah!® brand and products. The new trade name allowed the dimensional and typological range to be improved and an enhanced thermal performance if compared with Vitrocsa – now a competitor – to be achieved. At the time Jofebar decided to take this step, another competitor, Sky-Frame, was already showing significant progress in terms of thermal and air/water performance, so it was necessary to close this gap without compromising the functional and aesthetic competitive advantages of the panoramah!® system.

The PH38 sliding series was launched at Villa E (Geneva, Switzerland, 2008), by Christian Geissbühler. The first pivot door solution was installed in Casa F, in Lugano (2008), designed by Carvalho Araújo, for which a pivoting frame originally developed for the shop window of the Spanish brand Dynamobel was perfected. The PH38 version of the sash window appeared shortly afterwards in the AA/Origami House (Barcelona, ​​Spain, 2009) by Carlos Ferrater and Xavier Martí. Later on, a sash system was developed with the window pane retracting into the floor at Villa La Californie (2012), in the South of France, in a Norman Foster design. In 2010, a triple glazed sliding frame (2.60 x 2.60m) was installed for the first time in Villa B in Geneva (Switzerland), in a P-H Gindre & Associés design. However, the limitation of the PH38 series to a glass thickness of 38mm means, with triple glass, a maximum surface area of 7m². To overcome this limit, a more robust 54mm series was developed for Villa NHV in Vandoeuvres (Geneva, Switzerland, 2012), a dla designlab-architecture project [pp. 318-323]. The PH54 quickly became the most award-winning minimalist series ever, obtained the stringent Minergie certification, attributed only to windows of the highest energy efficiency.

From 2008 onwards, and from an industrial point of view, it also became more frequent for glass processors to be equipped with “Jumbo” tempering furnaces, which allow the tempering of larger glass (6 x 3.21m), somehow meeting the aspirations of many architects. It should be noted that the glass panes used are now increasingly larger than the 6m2 that were part of the initial proposal from Vitrocsa, and it becomes paramount to partner with a preferred glass manufacturer, able to work with standards of quality much more demanding than those that the glass processing norms define. This explains the relationship that Jofebar and the Vidromax/Maxividro group began to establish in 2006, deepening as this glass processor adapts its installed capacity to the needs of its best customer, and culminating in the acquisition of part of Jofebar in 2011. The remaining part was acquired in 2013 by the same shareholder that owns Vidromax/Maxividro and the process of integration and verticalisation of the activity that today has led to panoramah!® being the only manufacturer of minimalist windows in the world that processes and manufactures the main components of its system.

Projects in India – done in close collaboration with long-time partner Durall Systems – have since long explored large frame sizes. Specifically, the house in Juhu Beach (Mumbai, India) with windowpanes of 19m² and 6m-high – which corresponds to the Jumbo dimension – was, in 2011, the building with the largest sliding windows ever built. In 2012, also in India, 7.2m-high double glazing was installed in another house in central Mumbai. In 2015, the biggest triple-glazed glass pane (3 x 5.5m) was installed in a panoramah!® sliding frame at Villa D in Vaud (Switzerland) by Grégory Garcia. Also in 2015, in Alderbrooke, UK, the 8m height was surpassed, with 26m² double glass panes (8.2 x 3.2m), a solution that formed the prototype for the PH60 series, launched in January 2017. This series has been designed specifically to meet the requirements of the Migergie-P and Passivhaus standards. Moreover, it achieves larger glass dimensions and higher thermal performances, a requirement that led to the reconfiguration of the profile, altering the positioning of the thermal break section.

It should be noted that the assembly of the Alderbrooke window obliged appropriate machinery to be built for its installation. In situations where they lack greater strength due to glasses’ large size, aluminium profiles are modified and change proportions. There is a whole engineering process that leads to the design of structural components of great slenderness to ensure the desired structural performance. It is easy to understand, therefore, that this qualitative leap requires ever-increasing precision in manufacturing and assembly to ensure perfect operation since large glass panels need to be operated with great lightness and ensure ease of maintenance. This requirement, therefore, rests both on the prior meticulous calculation that has to be made specifically for each window – adjusting the profiles to the forces to which each frame will be subjected – as well as on the accuracy of execution of the structural bonding between glass and aluminium during manufacture and on overcoming the difficulties on each site. In fact, these are the attributes that distinguish companies specialising in engineering, manufacturing and assembly from the multinationals that are developing competitive systems. While the former maintain these processes, the latter have been forced to dumb down the product and consequently eliminate much of the added value that it offers.

Other less conventional forms have also been object for development, such as solutions with curved and oblique geometries. Curved double glazing was first tried in minimalist frames as a fixed element in the Salão de Festas in Cortes (Leiria, Portugal, 2008), by Marini Bragança. Later, the PH Curve product, with curved sliding windows, was launched for Casa Circulo in Begur (Girona, Spain, 2015). This product was also developed with a hidden rail solution, installed for the first time in an estate in Valle Bravo (Mexico, 2016). The triple curved glass was supplied to the Villa AT in Søgne (Norway, 2016) by Sauders Architecture. In the same year, conical double-glazed windows were also installed in a house in Quinta do Lago (Algarve, Portugal). As for the sloped solutions, Jofebar has created a prototype of 8m-high sliding windows, with sliding guides modified to allow them to slide with any inclination. This solution was developed for the project “The Sanctuary” by Zaha Hadid, a house in Uccle (Belgium, 2013) that did not come to fruition. However, the work done gave rise to the skylight or inclined window solution, included in the panoramah!® series PH54 Skylight, ideal for sloping roofs. First installed in a residential building in Stockholm, the product won the Red Dot Design: Best of the Best 2014.