## 4 Methods  
### Data Collection  
The results presented in this paper are based on data that were collected through analysis of the reports on the state of defects made by the inspector during the warranty period. The area of the conducted research included a total of 3 residential buildings. The buildings are part of various projects but were produced by the same developer and contractor. Two of them possess 16 aboveground stories, which are divided into 3 staircases with 172 flats, each with areas ranging from 29 to 117 m\({}^{2}\). These buildings were accepted in 2017 and 2018, which, in further analysis, coincides with the beginning of the research. The third building is a 6-story one, with two staircases and 73 flats. The time of the building's acceptance was August 2018. Details of the facilities analyzed are presented in Table 1.  
All buildings were finished to the same degree. The differences were in the type of finishing materials used in the common areas (that is, in staircases and the outdoor area). The development standard included plastering inside the premises, walls prepainted with white paint, screed, window and balcony joinery, entrance doors, embedded internal and external window sills, distributed ventilation system with diffusers for mechanical ventilation, distributed central heating installation together with installed radiators, water and sewage system without fittings, electrical installation together with plug and lighting sockets and switchboard, distributed teletechnical installation with a collective box, sockets and intercom, balustrades, and tiles on external floors. A precise definition of the elements of the shell unit standard is important in terms of warranty claims.  
The collected results of the research present an assessment of the validity of defect reports made by customers. The data are the result of actions taken by the developer, the supervision inspector, and the contractor. Each defect included in the statistics underwent verification of the original position of the developer. The role of the supervision inspector is to make an independent assessment and qualification of the report of potential defects by customers and managers of individual properties. The results of the research presented in this article are, therefore, based on expert knowledge.  
The collected data on warranty notifications cover the period from building acceptance in January 2018 and August 2018 to March 2020. A total of 560 notifications on the occurrence of defects during the warranty have been identified in the course of the conducted research. The collected data were analyzed statistically using GNU PSPP Statistical Analysis Software. First, the authors determined the percentage of valid and unfounded claims and, next, the percentage of claims under warranty cumulatively. Subsequently, the statistics of the three-stage qualification of defects were established--of low, medium, and high significance--as well as the relationship of defects to the place where they occur. The successive analyses concerned the type of defects. Pearson's parametric correlation and the determination factor R2 were computed to assess the relationship between the defects reported in different buildings and to establish the strength of the interdependence between different groups of defects.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Building** & \begin{tabular}{c} **The Number** \\ **of Stories** \\ \end{tabular} & \begin{tabular}{c} **The Number** \\ **of Staircases** \\ \end{tabular} & \begin{tabular}{c} **The Number** \\ **of Flats** \\ \end{tabular} & \
\begin{tabular}{c} **Total Area of** \\ **Flats (m\({}^{2}\))** \\ \end{tabular} &
\begin{tabular}{c} **The Time of** \\ **Acceptance** \\ \end{tabular} \\ \hline A & 16 & 3 & 172 & above 8000 & 2017/2018 \\ B & 16 & 3 & 172 & above 8000 & 2017/2018 \\ C & 6 & 2 & 73 & 3000 & August 2018 \\ Total & & & 432 & 19,000 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Details of the residential buildings.