The refurbishment of traditional vernacular architecture is currently of interest for the conservation of heritage, historic landscape and cultural landscape, as well as for its potential benefits in the field of environmental sustainability.
Given the threat of worsening climate change, the need for energy saving and for a reduction in CO2
emissions is currently a priority at a European and a global level 
, as reflected in the signing of the European Green Deal 
. According to official data from the European Union, over 40% of energy consumption is due to the heating and cooling of housing 
. However, the construction process also represents a sizeable expenditure in energy in the extraction, production and transport of building materials, as well as in the supposition of a phase of possible amortisation at the end of the life cycle in actions for the demolition and elimination of waste 
As is known, the numerous historic buildings of great heritage value are the bases of our history, culture and identity 
. Many of these buildings are now, or once were, dwellings standing alone or in groups in rural settlements or historic centres, and their refurbishment is essential for the conservation of our history and identity 
. This vernacular heritage architecture is not only important as a sign of identity linked to the landscape where it is born, but also for lessons in sustainability, which several authors have been promoting since the 1980s 
, according to the bibliographical review 
. In this regard, it is worth highlighting the project “VerSus: Lessons from Vernacular Heritage in Sustainable Architecture”, co-funded by the European Union between 2012 and 2014, which summarised the lessons in environmental, sociocultural and socioeconomic sustainability provided by vernacular architecture in 15 parameters, allowing the analysis of vernacular architecture cases and providing guidelines for the architectural design of new constructions 
. The conservation of this architecture is therefore important for the preservation of material, cultural and popular identity, offering continued inspiration with examples in sustainability 
. This project promotes international conferences focusing on these topics and becoming a source of major reflections in the field 
. This topic has also been covered in other publications on an international scale 
Regarding the first point, the extensive literature addresses the improvement of energy efficiency in the retrofitting of buildings. Nevertheless, almost all cases focus on housing built after the 1950s, according to the bibliographical reviews 
. Although these studies are of interest in the measurement and quantification of energy efficiency in existing buildings 
, they are somewhat limited in the application to buildings with heritage value which require the application of conservation criteria 
. Therefore, the notable differences between these refurbishments and conservation interventions on heritage buildings 
make it necessary to resort to other tools and guidelines used in the field of conservation 
, proposing practical examples of interventions for the improvement of energy efficiency in heritage and vernacular buildings. In parallel, several studies confirm the energy-efficient qualities of vernacular architecture as a type of architecture adapted to local surroundings and climate 
. It could therefore be said that interventions for improving energy efficiency in historic and vernacular buildings could be minimised, in turn reducing their potential impact on heritage buildings 
. On the contrary, transformations such as floods or stronger rains derived from climate change are putting this vernacular adaptation to the climate to the test, so that the adaptation of heritage to climate change is beginning to create new needs, questions and reflections 
In terms of the reduction in the CO2
emissions of architecture during its life cycle, it is increasingly claimed that the refurbishment, conservation, retrofitting and adaptation of existing architecture are more sustainable processes in terms of the environment and their possible effect on climate change than their demolition in order to build new constructions 
. Thus, there are growing numbers of guides and measures to prevent the production of CO2
as much as possible in building construction 
. However, in terms of LCA application to the retrofitting processes, once again these are mostly dwellings dating from the mid-20th century, according to the bibliographical review 
, and there are extremely few cases of this assessment being applied to heritage buildings 
. In the field of restoration and refurbishment of heritage architecture, different criteria entail the use of different types of traditional and industrial materials and techniques, 
and the impact on the environment can vary widely depending on the options, techniques and materials adopted in the project 
. In addition, the conservation of a heritage dwelling always prompts difficulties among all those taking part in the process (owner, developer, administration, etc.), given a lack of knowledge of the processes both during the intervention in the structure and the operation using traditional materials and techniques, as used in the past where they were part of local ancestral construction techniques found in the immediate surroundings 
There are still a few examples of refurbishment of vernacular architectures performed with traditional materials with the objective of preserving authenticity and, among them, fewer still which pretend to clearly demonstrate the impact that these alternatives from the conservation project have on CO2
emissions into the environment 
. Bearing this in mind, we aim to show that firstly, it is possible to use traditional materials and techniques in the conservation of traditional housing, and secondly, that the use of these traditional materials and techniques can impart major energy reduction in the conservation phase.
2. A Sustainable Approach for the Refurbishment Process of Vernacular Heritage: The Sesga House Case Study (Valencia, Spain)
The traditional architecture of Rincón de Ademuz was born closely of its surroundings and adapts to its conditions, as is the case of vernacular architecture in general. The towns are clustered on the south-facing slopes to prevent the occupation of the arable land in the valley, and dwellings tend to be two or three storeys high, towering over the buildings immediately below but allowing lighting and ventilation 
. The dwellings are generally built with masonry walls bonded with earthen mortar on the ground floor to prevent rising damp, while the upper floors are either thin, gypsum-rendered thin stone slab walls or sometimes rammed earth walls. However, the structure of the building is made up of gypsum structural pillars supporting rounded beams in juniper (Juniperus thurifera
L.), pine (Pinus nigra
) or poplar wood (Populus alba
). Both the floors with gypsum-poured jack arch vaulting and the roof formed with reed and ceramic roof tiles placed with clay and straw mix are supported by these beams. Stone slabs and gypsum are used for dividing walls and built-in furniture inside the building 
As all these materials are proximity materials, originally barely any energy would have been spent on transporting them to the construction site 
. In addition, many of the materials are used in the construction in their natural state, with almost no transformation, or with small transformations which also have a minimal impact on the environment, another lesson in sustainability to be learned from this vernacular architecture 
. Finally, the philosophy of the vernacular architecture essentially builds and resolves its problems with the materials found locally. This is in itself a philosophy which allows us to save on resources and transport while allowing contemporary architecture to re-establish contact with an identity linked to surroundings, something which has been lost over the last hundred years 
This vernacular architecture mostly uses gypsum as its only bonding agent, both because it is widely available in the surroundings and because it is five to seven times cheaper to calcine than lime in terms of fuel and time invested. This gypsum was manually calcined in the kilns near the towns and villages and mixed with a small amount of water to obtain a resistance capable of supporting up to four storeys 
Laboratory tests have confirmed these resistances, even using current commercial gypsum 
. Equally, a hundred pillars analysed in the region have provided information on the rubble infill used in the gypsum concrete of the pillars, dispelling any suspicion that the stones may have been commonly bonded with gypsum 
. Different accounts were also collected on the preference for the use of overcooked gypsum (anhydrite) in the construction of floors, given that this element was more waterproof.
The village of Sesga, where the restored dwelling is, and the dwelling itself answer to this description. The house (Figure 1
) is three storeys high, with masonry enclosures on the ground floor and vertically placed stone slab walls on the upper floors. The pillars of the structure rise up from the masonry wall to form floors and roof with the help of pine and juniper beams and pine and poplar joists. Samples extracted from the beams have dated the construction of the original single-storey dwelling to circa 1732 
. The wall adjoining the neighbouring building, built with rammed earth, lies under this structure so that it is suspected that it could be a century older. In 1947, another storey was added to the dwelling and the adjoining volume was built over a pre-existing courtyard, using the traditional techniques previously described 
Figure 1. The house before the intervention. Credits: C.M., F.V.
This lengthy refurbishment of a vernacular dwelling using traditional construction materials and techniques which have been reinterpreted was proposed from the outset as an experiment, a pilot conservation action which could be visited in order to showcase the results to local residents and society in general. The three-century-old building was initially in an extremely poor condition (Figure 1
) and at severe risk of collapse, with collapsed areas in the roof and flooring which let snow through to the ground floor 
Criteria Used for Decision Making
The refurbishment mostly employed natural materials including gypsum, lime, wood, reed, cork, etc. The structural reinforcement used local timber to replace beams and braces that had rotted away or to build the joinery missing from the house; local timber and natural glues were used in the restoration of the doors and the joinery found in the house; reeds were used to reinforce the gypsum and to form the basis of the roof; lime was used to consolidate and grout the rammed earth wall; gypsum was used for the repair or reconstruction of some collapsed small vaults and to build compression layers reinforced with reed meshes or twine 
. Gypsum rendering was reinforced with twine. Lime mortar was used to rejoint any masonry walls requiring structural reinforcement and for the ground floor flooring. Clay and straw were used to place the tiles recovered on the roof. Pressed cork panels were used for the thermal insulation of the walls and local-made brick was used as secondary wall to better insulate enclosures and to build new interior partition walls. Other less important materials were used following the same type of priority 
After the structural strengthening, the aim of intervention was to update contemporary habitability standards while preserving the vernacular nature of the building as much as possible, respecting its handcrafted finishes, the outlines of its construction, as well as the textures, qualities and patina of its materials. At the same time, efforts have been made from the outset to remain as much in line as possible with the sustainability parameters observed in vernacular architecture and coded in the VerSus Programme 
, with the SDGs 
and with the traditional life cycle of the materials usually used in the local vernacular architecture.
The specific actions carried out were:
Historic finishes have been respected. Any existing bare rough stone or stone slab walls have been maintained and any existing gaps have been jointed.
Interior gypsum-rendered walls have been re-rendered after adding thermal insulation and new walls. Extremely fast-setting gypsum was used as rendering, following tradition and leaving the natural marks of the trowel.
Flooring had a waxed gypsum rendering, recovering an almost-extinct local tradition.
Double-glazed wooden windows were added where previously there had only been wooden shutters.
The inner doors of the dwelling are small historic doors which have been repaired, including a charm against evil spirits in the form of three candle burn marks. The low doors make it necessary to duck when entering the room, as if revering the history of the space.
The refurbished vernacular house shows off the beams and the construction of its floors, ceilings and reed roof (Figure 2). The exterior façade, with a stone masonry plinth on the ground floor and rendered in reddish gypsum on the upper floors, conserves the same appearance and finish as before the intervention (Figure 2). Behind a façade, which still preserves the vernacular appearance of three centuries ago, there is a house with all the characteristic standards and installation of a contemporary dwelling but largely preserving its character. This has set a precedent with a clear message, especially for local residents: it is possible to preserve ancestral material culture while also carrying out the refurbishment of homes to be used in the present.
Figure 2. State of the house after refurbishment of its external facades and internal spaces. Credits: C.M., F.V.
The results obtained provide evidence that the qualitative criteria (VerSus) used to include sustainable principles in the design process of the refurbishment project are supported by the lower values in the quantitative assessment (LCA).
The refurbishment of this simple vernacular single-family house shows that it is not necessary to invent new building techniques, materials and processes; a contemporary approach reinterpreting the vernacular techniques and materials suffices to meet all objectives at once: mitigating climate change as seen from the LCA is carried out; this co-creation process involves the architect, owner and master builder, but also history, tradition, material culture and the idiosyncrasy of local materials. For example, the process of reinforcement of floors and roof incorporated a gypsum compression layer which was reinforced with locally sourced natural fibres (straw, wool, hemp, reed…). Samples were extracted from all these and tested in laboratories to decide which combination offered the best results, subsequently using it on site. Materials were all local and traditional, with a low carbon footprint, although the execution was contemporary. The structural properties of the reinforced floor were on a par with those of a floor built or reinforced with cement-reinforced concrete.
This all shows the potential of refurbishment using natural materials over refurbishment using conventional industrial materials or over a new construction following demolition of the existing dwelling. The application of these principles in the field of construction could significantly affect SDGs and related environmental, sociocultural and socioeconomic aspects, as well as helping to reduce the environmental impact of new construction.
The results obtained also provide evidence of the potential environmental advantages that vernacular techniques and natural materials have in the context of Valencia (Sesga), which have not been explored before. In short, it is demonstrated that vernacular construction can be developed as a contemporary option for housing in this region.
The refurbishment work of Sesga single-family houses based on natural materials has been demonstrated as the best solution to reduce the environmental impacts of building construction in this region, compared with the use of conventional industrial materials either in refurbishments or in new buildings, that are the two most common options not only in the village, but also in the whole region. Moreover, the study demonstrates that the combination of qualitative (VerSus) and quantitative (LCA) criteria can help to reduce the environmental impacts and integrate sustainability criteria in the design process. Furthermore, this refurbishment resorted to the use of traditional materials and techniques and the reinterpretation of their systems for the structural strengthening of walls, floors and ceilings, as well as final finishes. For example, based on the knowledge of traditional gypsum and its analysis in specialist laboratories 
, systems were created for the strengthening of floors and ceilings using gypsum compression layers reinforced with reed or hemp string, among other natural fibres used in experiments both on-site and in the laboratory. There were also reinforced renderings of the same type with fibres to prevent bulged walls from collapsing. Following older local builders, gypsum samples tested in the laboratory displayed the same or even greater resistance than a current reinforced concrete structure 
. This use of gypsum and natural fibres conceived as contemporary reinforcements seeks the same physical–chemical–mechanical compatibility as that of a human organ transplant, as the same phenomenon of rejection of the implanted organ could be generated in the refurbished building. However, several limitations in the assessment and integration of qualitative aspects in the design process are detected. Qualitative methods demonstrated the economic and social benefits of using these techniques. However,, the life cycle perspective still remains scarce. Nevertheless, it should be noted that the materials traditionally used in these houses built more than two centuries ago have reached the present day, so it does not seem unreasonable to hypothesise that the same materials used today could last at least as long. Thus, the integration of other quantitative aspects in the design process can be a future topic to be addressed.
This case has value in the specific context of the village of Sesga and the county of Rincón de Ademuz, but it also has a wide possibility of application in similar contexts in Spain and other European countries 
. Spain is currently one of the European countries that suffers most from depopulation of rural areas, with 52% of the population living in cities of more than 50,000 inhabitants, while only 3.2% live in municipalities with less than 1000 inhabitants 
, a phenomenon currently called “Emptied Spain” 
. In the rest of Europe this same phenomenon has been worsening in several rural areas, especially in Italy, Portugal, Greece and Germany, concerning the European Union 
, at the same time that it is trying to reduce CO2
. In this context, the renovation of homes with natural materials meets several objectives: showing the possibility of respecting and preserving a vernacular building as part of history and identity and updating it for contemporary life; using natural materials that are extracted and worked locally by creating work opportunities for local trades; helping to promote local activities and to fix the population in rural areas; and lastly, reducing CO2
The entry is from 10.3390/su13179800