6 social housing units on rental basis
21 Ses Monges St., Santa Eugènia, Mallorca
ENVIRONMENTAL INDICATORS/
- CO2 emissions: 304,67 kg/CO2 x m² 59.4% reduction compared to an average value for all types of buildings of 750 kg CO2/m², calculated by SO. A total of 257,810.44 kg CO2 avoided. .
- Combined cooling and heating energy demand: 4,80 kWh/m² 84% reduction compared to the passive house limit of 15.00+15.00 kWh/m. Lifetime emissions associated with energy demand are 0.85 kg CO2 x m² per year, with total annual savings of 2,192.57 kg CO2. .
- Waste during the works: 20,11 tn (0,03tn/m²) 50% reduction compared to the theoretical calculation for an average equivalent building. .
- Water consumption during useful life: 88 liters per person and day 30% reduction compared to the average consumption in the Balearic Islands, according to INE.
CONCEPT/
This social housing is a prototype to refine and demonstrate the feasibility of local low-carbon materials in simple compression structures, recovering a model in which ‘the quality of architecture comes from stacking the mass, instead of the transformation of the physical and chemical qualities of the materials’ (A. Cuchí, 2007)
URBAN CONTEXT/
Santa Eugenia is a small, picturesque town, 20 minutes away from Palma. Landscape integration was essential to eradicate the stigma suffered by social housing in Balearic Islands. However, landscaping has not been solved from the form, but from the use of local low carbon materials and the update of vernacular construction techniques as the most efficient way to use these resources. When the works were finished, some surprised neighbors said:
‘They have not spoiled the town!’
PROGRAMME AND CLIMATE/
There are three homes on the ground floor, and three homes on the first floor. The access to the dwellings is through the rear courtyard to provide a common space as green as possible, and to improve the sense of community. In addition, all the dwellings have a little private outdoor patio at the entry.
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The climate in Mallorca is Mediterranean semi-arid and the risk of drought is expected to increase with climate change. Green areas and bioclimatic devices are important parts of the thermal functioning of the building; thus, it is important that these areas can continue to thrive in drought and high heat without a significant increase in the building’s water use. Hardy native plants with low water requirements were selected for this reason and are irrigated with stored rainwater. Two pre-existing trees have been preserved on the site -a Mediterranean hackberry and a pomegranate-.
NEW PRODUCTIVE MODEL AND REPETITION/
Global CO₂ emissions have increased from 5 Gigatons (Gt) to 37 Gt per year in the last century (GPC, 2022).
The Earth, through sea and land can only absorb 19 Gt of CO₂ per year, which is equivalent to the world’s available carbon budget. Therefore, twice as much is spent as is available.
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Green Building Council (GBCe) has calculated the carbon budget for the building sector in Spain, and to meet the European Commission's binding decarbonization targets, a 52% reduction in emissions is required by 2030 and 92% by 2050. Designing with a carbon budget is a complete game changer.
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One option to achieve this reduction - within this 5-year period - consists of recovering the capacity to build with the territory itself, seeking the greatest possible self-sufficiency under the paradigm of degrowth and global social justice: the recovery and preservation of local low-carbon resources, local industries that promote energy transition, up-cycling of resources previously considered waste, etc. These strategies are part of the ‘Resource Map’ and enable embedded CO₂ reductions that immediately meet the 52% target. Moreover, these local resources impose limits: how much can we build and what kind of uses should we prioritize?
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The Santa Eugènia project is the 2.0 update to 8 social housing units in 39th Salvador Espriu St, in Palma (2018-2021), and develops the research of a new production and consumption model based on the ‘Resource Map’, initiated in Reusing Posidonia (2012-2020), a climate change adaptation project funded by the LIFE+ program from the EU, in whose process of monitoring the houses it was found both the need to incorporate mass to have inertia in summer, as well as the unnecessary nature of active heating systems in well insulated buildings in the Mediterranean climate. It is a continuous process of learning and improvement through repetition, whose objective is to develop, step by step, a more refined, easier and faster low carbon building system.
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The two main improvements over the previous projects are a greater reduction of the combined energy demand -cooling and heating- through exclusively bioclimatic systems, and the standardization/repetition of construction elements to minimize the short-term economic investment of local low-carbon materials: sandstone in structure and facades, FSC wood for trusses and carpentry, interior carpentry of reused wood, Posidonia oceanica (Neptune grass) as roof insulation, etc. In this case, all the spans between pilasters are equal (160cm) to facilitate the execution of the building. The same applies to the window openings, which have been arranged on vertical axes to simplify the construction of walls and lintels.
MAP OF RESOURCES AND COMFORT/
The main priority is comfort and minimizing energy poverty through bioclimatic solutions and locally sourced materials. Total heating and cooling energy demand is calculated at 4.80 kWh/m². Even in a +2°C scenario (Paris Agreement limit) for the period 2041-2070, a combined cooling and heating demand of only 6.4 kWh/m² is expected. Domestic hot water (DHW) is heated by aerothermal pumps and photovoltaic panels. However, energy efficiency comes from the architecture itself:
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-In summer, the passive strategies are inertia (mass) and hygrometric comfort provided by the stone, cross ventilation facing the prevailing breeze from the sea (Embat) with the support of ceiling fans, sun protection through traditional wooden shades, and thermal insulation of 10 cm on walls and 24 cm on the roof.
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-In winter, the passive strategies are very thick thermal insulation -for Mediterranean climate-, and many windows to collect as much sun as possible. Air renewal is provided by a low-tech convection ‘Trombe’ wall (powered by a 50w fan) facing south, towards the neighboring plot, which is unbuildable according to current urban planning regulations. During the cold months, the outside air is tempered by convection in the Trombe wall and dis¬tributed to the six homes by mechanical ventilation through individual pipes for each dwelling.
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The building’s comfort is being monitored in collaboration with the University of the Balearic Islands (UIB), both to check and refine the efficiency of the system for future projects, and to provide reference values for future regulations.
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Following a mapping of resources, 50% of waste production was avoided during the construction phase, and 59,4% of CO2 embodied emissions were saved during construction, thanks to sustainable sourcing and the urban mining of a small pre-existing shed on the site, the construction elements of which have been entirely repositioned in the new work: shutters, doors, tiles, and sandstone-reused in the plinth of the building, with the cut marks exposed as TEd'A showed us a few years ago at Can Jordi i n’Àfrica-. All interior doors and partitions are made of wood from demolition. The reused solid wood boards of the pitched roof structure come from an old factory and support the 25 cm insulation of Posidonia oceanica. This insulation, with λ=0.044 W/mK, makes visible that ‘we do not live in a house, we live in an ecosystem’.
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The use of the leaves of this marine plant endemic to the Mediterranean, considered a priority habitat by the EU, requires the permission of the competent public body, and they can only be collected by authorized managers in March-April, since the dead leaves deposited on the beach protect the dune ecosystem from winter storms. Once on site, the leaves are dried in the sun without any additional treatment and compacted by hand in bulk on the roof of the building. Due to its chemical composition, there is no terrestrial predator that can affect it, due to the content of phenolic compounds, sulfides and sulfites, which are phytotoxic.
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The local ‘marès’ sandstone is low-carbon, it provides mass and endurance to extend the useful life of the building and is 100% reusable.
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The three homes on the ground floor are organised in two parallel 3.5 metre stone barrel vaults supported on three axes of pilasters with a base of 40x80cm, also made of stone. The rooms can be marked out using movable wooden doors that are the size of walls.
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The facades are solved by two parallel self-supporting stone walls, each 10 cm thick, with intermediate thermal insulation of 10 cm of recycled cotton, which is confined between two breathable waterproof sheets, the inner one being Intello type with variable SD value. The inner wall holds the vault pilasters, and the outer wall protects the insulation package. To reduce the number of anchors between walls, the outer stone sheet has pilasters that protrude 10 cm and increase its rigidity and stability. There are only two stainless steel anchors per pilaster, to facilitate the supervision of the execution on site, and they are located at the starting level of the lintels of each floor. The construction defines the expression of the building.
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The three homes -on the upper floor, with independent access and staircases for private use- are organised in a single open space, in this case under the pitched roof supported by wooden ‘spanish’ trusses with 9.6 metre spans, with wooden partition walls -and acoustic insulation- defining 2 bedrooms, each with two doors.
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One of the main improvements of the project to build faster is the upgrade of the mortar for the joints, which has been studied so that several stone blocks can be stacked on the same day with a crane without the need for wedges and will not be crushed by the weight of the blocks themselves. To facilitate the construction of the vault, one-piece stone lintels have been used between pilasters from a different quarry that provides a stronger stone and weighs approximately 840 kg per unit.
GENDER-SENSITIVE DESIGN CRITERIA/
The rooms are not hierarchical. All the rooms are the same, avoiding the division between double and single bedrooms, there is no en-suite bathroom, and they have a generous surface area so as not to determine their activity, with a size of between 12 and 13 m² to include storage space.
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The kitchen is located in a central place of the house, integrated with the common spaces of the living area, with visual connection between all the spaces to make visible the cures and the domestic tasks.
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The distribution through mobile partitions of reused wood is flexible and adaptable to the different stages and family circumstances, allowing the transformation and evolution of the house in a simple way, without the need for construction work. Lifespan is one of the main strategies of circularity of this building and requires flexibility of uses very easily over time. Interestingly, apparently rigid stone structures, combined with wooden partition walls, have generated a flexible floor plan.
SELF-SUFFICIENCY AND CITY/
Self-sufficiency in construction processes blurs the boundary between the productive space of the city and the productive space of the countryside, because the city is built with materials from the adjacent territory. Before the Industrial Revolution, farmers never had to worry about landscape integration. The recovery of cultural heritage becomes a tool both to meet the objectives of decarbonization and to recover the notion of the city as a sum of anonymous and silent interventions.
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Recently, public and private developers have built more than 300 houses in the Balearic Islands using local stone in structural elements. Thanks to the efforts of local and non-local architects, committed to the recovery of local low-carbon resources, some sandstone quarries have invested significantly to update facilities and increase the number of workers, with the aim of avoiding extinction and maintaining the trade: in the last 12 years 12 quarries had closed. One of the next collective steps being worked on is the development of methods to apply these materials on a larger scale and in a new context of labor shortage that has accelerated since COVID-19 and the lack of housing.
