## 1 Introduction
### Sustainability Assessment Methods  
The knowledge generated by these indicators can be oriented towards the creation of methods and certification tools that measure sustainability and introduce policies to improve the environmental performance of buildings. Focusing the analysis on sustainability assessment methods for residential buildings in Europe, one of these policies is the implementation of GPP [17]. Another involves the application of Level(s) [73], the European framework for sustainable buildings. This builds upon the objectives of both the EU Green Deal [74] and the EU Circular Economy Action Plan [2]. As a voluntary initiative, the Level(s) framework aims to promote a common language across Europe to assess and report on the sustainability of buildings. This framework proposes several indicators covering three main areas: resource use and environmental performance; health and comfort; cost, value, and risk. These have been developed based on existing standards as well as on a life-cycle approach to measure and support improvement through construction, use, and end-of-life phases for residential and office buildings. Another initiative in the EU is a French proposal, Energy-Plus and Carbon Reduction Buildings (E+C-) Trial Scheme [75], whose main goal is to reduce the overall CF of buildings by using low-carbon and energy-efficient materials. In Italy, the compulsory minimum environmental criteria (CAM) [76] contain technical specifications for materials and components, thereby clearly promoting the circular approach in construction. In particular, CAM requires a minimum of 15% recycled content in the materials used for each construction/refurbishment intervention. They also set specific minimum recycled content thresholds for seven types of materials and require product certifications, such as environmental product declarations, environmental labelling, and producer declarations, in order to prove that products are \"CAM\" compliant. The criteria are mandatory for any type of building intervention in public buildings. Another Italian tool is the Itaca Protocol [77], which assesses the level of sustainability of buildings with reference not only to consumption and energy efficiency, but also taking into consideration their impact on the environment and human health. In Spain, there are no mandatory methods created by the administration that promote GPP. There are private initiatives, such as HADES [78], which is a free method that helps in the design of buildings of a more sustainable nature. HADES is mainly oriented towards housing, although it can also be used for offices and equipment. It evaluates energy, materials and the circular economy, water, indoor environmental quality, and climate change. Another tool is VERDE [79] (Valoracion de Efficiencia de Referencia de Edificios), also developed by GBC Spain, and this method aims to provide a methodology for the evaluation of the sustainability of buildings. It is a methodology that enables buildings to be conceived in a global way while including all their phases. VERDE develops tools for residential buildings, offices, rehabilitation, etc. The LCA of the building is carried out whereby the potential impacts are weighted in absolute values, and these are subsequently associated with one of the six levels of certification through a comparison with a reference building. The CO emissions caused by the manufacturing of materials employed and by the operational energy consumed are evaluated by LEED y BREEAM, which is the first initiative managed by GBCe [80], and by the second initiative known as BREEAM Spain [81]. Its methodology is based on the determination of impacts classified by categories, although these impacts do not conform to the LCA. At the end of the process, like VERDE, it is the accredited certifier who calculates the rating of the building. Another method available in Spain is ECOMETRO [82], which is an open source for the design, environmental assessment, and measurement of LCA in buildings.