Public Property

Salvador Espriu social housing by IBAVI under construction in the periphery of Palma de Mallorca

[Originally published in The Architectural Review in April 2022]

Before the arrival of steel and concrete, the most widely used building material on Spain’s Balearic Islands was marés, a sandstone formed in the Pleistocene by the compression of sea-sand and seashells, whose calcium acted as a bonding agent. This beige stone hides just below the surface of much of Mallorca and Menorca, revealing its stratifications along their rugged shores. Extraction of this stone, which dates as far back as the ancient Phoenicians, was originally from the coast, where it could be shipped by barge to construction sites. Traces of shore extraction are still visible in the form of orthogonal rock formations. In the Middle Ages, marés was shipped from these islands to as far as Perpignan and Naples, where Mallorcan kings and later the Crown of Aragon built royal palaces and castles. Eventually, with modern machinery, marés extraction moved inland, where over a thousand open-pit quarries abound to this day, although very few remain active.

Marés was used in the Balearic archipelago until well into the 20th century for just about every type of construction, whether monumental or utilitarian. Palma’s splendid cathedral completed in 1346 and its beautiful Llotja, a trading centre completed in 1452, are built of this stone, as are its defensive walls, countless houses, rural agricultural sheds and the many historical windmills that dot Mallorca’s landscape. Marés was simply the most readily available building material on these islands – the vernacular equivalent of brick or timber frames elsewhere. With the arrival of modern construction techniques and the development of larger building types, marés construction was rendered obsolete, relegated to a more decorative role at 1960s sun, surf and sangria holiday resorts.

A notable exception is Can Lis, the house Jørn Utzon completed for his family in 1972 after returning to Europe from his bitter experience building Australia’s Sydney Opera House (AR February 2019). Can Lis is an ensemble of pavilions united by garden walls, porches and patio courtyards, with modern precast-concrete joists and ceramic bovedillas (a type of hollow block) supported by marés cavity walls and piers that moderate daylight and frame sea views. The villa was restored in 2012 by Danish architect Lise Juel with local firm Aulets Arquitectes, and is today a canonical example of mid-century modernist architecture employing stone in a structural role.

Can Lis, Mallorca, by Jørn Utzon, 1972.

In the climate of conspicuous consumption of the 1980s, marés became the stuff of luxury holiday homes, a rarefied material supplied by the few quarries remaining in operation. However, marés is now being revived as a mainstream building material by the Instituto Balear de la Vivienda (IBAVI, the Balearic Housing Institute), a government agency responsible for delivering social housing on the islands. IBAVI periodically designs small social housing projects for the purpose of field­testing new methods and materials that can eventually be applied in larger housing projects commissioned through national architectural competitions. Some of IBAVI’s past in-house projects have experimented with non-fossil-fuel fired bricks and tiles, wooden doors that have been recuperated from renovated or demolished buildings, and dried Neptune grass thermal insulation, such as at their social housing project on Formentera (AR July/August 2019).

Through a process it has developed whereby the carbon emissions of different building materials are ‘resource mapped’ according to geographic location, IBAVI has discovered that marés construction outperforms other kinds when sourced nearby. IBAVI first tested this material in 2019 at Carrer del Regal, a three-storey urban infill social-housing project in Son Gotleu, an inner-city immigrant neighbourhood of Palma, in which load‑bearing stone walls work in structural combination with timber and concrete horizontal elements.

More recently, IBAVI has begun to test marés vaulting in an effort to minimise concrete and imported timber. Completed this year, the Salvador Espriu residential building on the periphery of Palma is the first of these experiments. ‘Marés construction not only lowers local carbon emissions by 60 per cent compared with concrete, but greatly improves thermal inertia, and therefore comfort in our Mediterranean climate,’ IBAVI architect Carles Oliver explains. ‘Marés is porous, so it regulates humidity and temperature in conjunction with cross‑ventilation, Neptune grass insulation, exterior wooden shutters and heat recovery units.’

Salvador Espriu social housing by IBAVI under construction

Containing eight affordable flats for households suffering from energy poverty, Salvador Espriu is an elongated two-storey building, in which a pair of parallel vaults, each spanning around 3 metres in width, separate the ground floor dwellings from those on the upper floor. The architecture of this building has been conditioned by the requirements of these structural vaults, determining dwelling layouts and spatial uses. The two parallel vaults are joined by a concrete girder that runs from party wall to party wall down the centre of each dwelling, an intermediate support for which is provided in the form of a stone structural core containing a bathroom. This core generates different domestic spaces: a living room on the side that is closest to the entrance and, opposite, a large bedroom that can be divided into two smaller bedrooms.

Considerable buttressing is required for such heavy vaults, which has generated a regular rhythm of deep niches inside dwellings along exterior walls. These niches have been used for cosy window nooks that open onto private rear patios, kitchen counters and built-in storage. The unusual structural system forms the very architecture, rather than – as is much more typical today – a structure driven by formalist or functionalist imperatives. Here, form follows structure.

Another IBAVI-designed residential building is currently under construction in the Mallorcan rural village of Santa Eugènia,  similarly based on a structural system comprising a pair of parallel vaults between upper and lower floor dwellings. A colonnade of stone piers supports stone lintels, replacing Salvador Espriu’s concrete girder and stone core. The marés vaults of this building are even larger, with no concrete visible. Here, a wider variety of domestic configurations has been enabled. ‘Santa Eugènia is the most optimised project to date in terms of carbon reduction, domestic adaptability, as well as cost effectiveness,’ Carles Oliver explains. ‘It is the culmination of all our research to date.’ Flexibility, eco-efficiency and affordability where every wall and pier is load-bearing? Le Corbusier must be turning in his grave.

Santa Eugenia social housing by IBAVI under construction

In dense urban environments such as Palma’s Son Gotleu, where land values are higher, dwellings containing rows of thick stone piers are less feasible – the reason that concrete girders and imported timber are used in urban projects, including in Salvador Espriu. IBAVI’s ‘most optimised’ vaulted stone project in construction in Santa Eugènia is, crucially, situated in a rural environment, where land values are lower.

One Mallorcan marés quarry that was on the verge of shutting down is reportedly modernising its entire operation thanks to renewed demand generated by IBAVI’s programme of 250 dwelling units employing this material. Who would have thought that one of the oldest, most artisanal and labour-intensive construction materials would be used to build social housing in the 21st century? It is remarkable to see public-sector architects democratising a building material that, once widely used, became luxurious and rarefied. Social housing has never looked so dignified.

With each subsequent project, IBAVI pushes the limits of materials and design one step at a time. Such an empirical approach, which involves a great deal of performance monitoring, data collection and critical analysis, is paramount if architecture is going to lead the way towards decarbonising the building industrial complex. IBAVI’s architects are perfecting a radically ‘new’ construction system – one that stands to transform building-as-usual, at least in this little part of the world.

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