## 2 Materials and Methods
### Analysis of Construction Technical Solutions  
Following the collection of the general set of technical solutions, those related to the energy efficiency target were categorized into the following types:  
* external wall insulation;
* roof/terrace insulation;
* external window replacement.  
This categorization facilitated the development of a portfolio of solutions, offering an overview of various intervention alternatives and enabling effective comparisons.  
For each solution, the associated construction products were identified and analyzed. Each product was examined based on its technical characteristics, including material composition, dimensions, supply specifications, and performance. Furthermore, the analysis highlighted the presence of environmental product certifications and key attributes for evaluating product compliance with sustainability criteria from a life-cycle perspective, such as durability, environmental impact, and features related to installation and disassembly.  
Comparison Between the Observed Building Products and Sustainability Criteria for Material Selection  
As previously mentioned, the interventions carried out under the SINFONIA project adhered to the KlimaHaus R protocol, which is specifically designed to evaluate the energy performance of buildings undergoing renovation. However, this protocol does not account for the environmental impact of materials. Consequently, this study references the KlimaHaus Nature protocol, proposed by the KlimaHaus Agency, which is compatible with the existing certification framework.  
The KlimaHaus Nature Technical Guideline, particularly in the section titled \"Environmental Impact of Building Materials\", introduces the ICC indicator. This indicator calculates the environmental impact of building materials and products used in the building envelope through a dedicated calculation program. The ICC indicator evaluates four parameters: Non-renewable Primary Energy (PEI nr), Acidification Potential (AP), Greenhouse Effect Potential (GWP100), and Material Durability (Time of Use, tu).  
For specific values of environmental parameters, reference is made to data available in the KlimaHaus database. Where a material is not included in the database, similar materials are used as substitutes. If the product being evaluated has an EPD compliant with ISO 14025 [70] and EN 15804 [71], the certified environmental parameter values in the declaration can be directly input into the calculation program.  
The calculation program assigns bonus points for factors such as the proximity of production, processing, and supply sites to the construction site; the use of materials with third-party environmental certifications (environmental product label Type 1 according to ISO 14024 [72]; and materials produced in facilities certified with the Klima Factory label. Additionally, the Guideline specifies materials that are not permitted for Naturecertification, such as products containing ozone-depleting substances, plastics with heavy metals or organic tin compounds, and tropical wood lacking FSC or PEFC certification.  
The KlimaHaus Nature indicators for building materials are summarized in Table 2 (see Section 1.2). Based on these criteria, the technical characteristics and product certifications contributing to the fulfillment of these requirements were highlighted in the data sheets of the materials used in the analyzed projects.