# BEST--Building Energy-Saving Tool for Sustainable Residential Buildings
## 2 Materials and Methods  
The overarching goal of this research is to enhance the energy efficiency of the national residential building stock, with the aim of developing high-performance buildings aligned with the energy transition objectives set by current regulations. The study focuses on the development of a tool designed to assist designers in identifying the most suitable retrofit solutions based on the building's construction period, typology, structural characteristics, and climatic zone. The outcomes of previous research efforts have provided the foundation for the development of a decision-support tool for energy efficiency interventions in residential buildings undergoing renovation [37]. The tool is built on an Excel-based computational engine with macros in Visual Basic, integrating pre-calculated solutions through a dynamic matrix consisting of 718 configurations, in accordance with the parameters established by current regulations (Supplementary File S1). Leveraging an optimized solution database, the system enables the selection of standardized, efficient, and sustainable technologies that meet the regulatory performance requirements for wintertime building performance, with reference to off-site construction practices. The tool offers a preliminary energy analysis, allowing users to assess the impact of retrofit interventions on the building envelope by providing insights into potential energy and cost savings. Through performance simulations, professionals can compare different optimized solutions, supported by a dynamic matrix that integrates criteria related to the existing building envelope and regulatory requirements. The calculations include heating and cooling energy demands, considering both the envelope and the most common HVAC system types. A key feature of the tool is its ability to select vertical and upper horizontal enclosures based on specific criteria, thereby simplifying the complexity associated with defining layer compositions. The proposed energy efficiency solutions, tailored to each case, allow for the calculation of economic savings, NPV, and available incentives. Additionally, users can download detailed reports containing stratigraphy information, simulation results, hygrothermal performance checks, and sustainability indicators. In the table below (Table 2) the functionalities of the BEST tool are presented. The methodological approach underpinning this research is based on the definition of a flowchart that identifies the fundamental input data necessary to guide designers in selecting the most appropriate case scenario for the building to be retrofitted. This classification is based on construction period, building typology, structural characteristics, and climatic zone. Figure 1 presents the methodological framework, outlining the key steps followed in the tool's development. The activities and findings from previous research, essential for generating a database of optimized pre-calculated solutions, are highlighted in grey. In particular, these first three steps represent the preliminary phase of the development of BEST. This phase is focused on building the technical and knowledge base required to generate effective energy retrofit solutions. A detailed description is provided below:  
* _Step 1--State of the art of the main types of Upper Horizontal Closures (UHC)_: The first step involves a comprehensive analysis of the state of the art and a typological classification of UHCs based on the buildings' construction periods. The objective of this step is to build an organized database that identifies the most recurrent construction solutions for each historical building era. The outcomes include a typology table of UHCs by construction age and a systematic classification matrix that will support the subsequent selection of appropriate retrofit interventions. * _Step 2--Study of insulating materials through a sustainable approach_: The second step focuses on the study of insulating materials with a strong emphasis on sustainability.