## 4 Safety and Sustainability Assessments of U-Shaped Stair Projects: A Case Study
### Decision Makers  
When choosing a staircase design for a single-family house, it is important to consider the opinions of architects and interior designers, to ensure that the structure, form, dimensions and aesthetic features of the staircase are in harmony with the existing spatial layout or interior-design decisions. For original and specific staircase projects that are going to be implemented in the open-plan living area, consultations with engineers are recommended, to ensure the appropriate selection of staircase-support elements. The expertise of staircase company specialists may complement the preceding expertise, as staircase sellers have a direct linkage with house owners and an extensive knowledge of customer needs, behavioural tendencies, usability, and safety and durability demands. Finally, experts in environmental protection and fire safety possess valuable knowledge regarding the sustainability of staircase materials, as well as fire safety features.  
Considering the previous reasons, seven experts (DM 1-DM 7) were invited to participate in the study case. They are:  
* DM 1 and DM 2. Architects who can assess the overall visual and aesthetic value of the building, and advise on the design, shape, and proportions of the staircase;
* DM 3. An engineer who can advise on the design of the staircase and the choice of materials, taking into account the strength, stability, and weight of the staircase;
* DM 4. The specialist of the staircase company who can assess staircase safety, design, choice, and other aspects;  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Alternatives** & **Staircase** & **Handrail** & **Steps on** & **Stair Width** & **Step Height** & **Tread** & **Lighting** \\  & **Material** & **Construction** & **Landing** & **cm** & **Width, cm** & **Coating** & **Lighting** \\ \hline A1 & Steel & Side mounting, horizontal infill (s/h) & 2 & 80 & \(15\times 25\) & Ceramic & E and N \\ \hline A2 & Wood & Top mounting, vertical infill (t/v) & 0 & 120 & \(17\times 29\) & Carpet & SW and SE \\ \hline A3 & Reinforced concrete & Top mounting, horizontal infill (t/h) & 4 & 100 & \(15\times 30\) & Wood & W and N \\ \hline A4 & Reinforced concrete & Side mounting, vertical infill (s/v) & 3 & 90 & \(18\times 25\) & Ceramic & E \\ \hline A5 & Wood & Top mounting, horizontal infill (t/h) & 0 & 110 & \(17\times 29\) & Wood & N \\ \hline A6 & Steel & Side mounting, vertical infill (s/v) & 1 & 70 & \(18\times 30\) & Carpet & NE \\ \hline A7 & Steel & Side mounting, horizontal infill (s/h) & 3 & 70 & \(18\times 30\) & Wood & No windows \\ \hline A8 & Reinforced concrete & Top mounting, vertical infill (t/v) & 4 & 100 & \(17\times 29\) & Ceramic & No windows \\ \hline A9 & Wood & Side mounting, horizontal infill (s/h) & 3 & 80 & \(18\times 25\) & Carpet & No windows \\ \hline \hline \end{tabular}
\end{table}
Table 3: Description of alternatives representing U-shaped stair projects in single-family house.  
* DM 5. An environmental specialist with expertise in sustainability for construction projects. The choice of stair materials and their environmental impact could be advised upon by this expert;
* DM 6. A fire safety expert who can advise on the type and materials of the staircase in relation to the building plan and other aspects related to preventing fire;
* DM 7. An interior designer who can advise on the choice of stair coverings in terms of style, functionality, and lighting solutions.  
All these experts were asked to determine the final list of criteria related to the analysed topic, to conduct a pairwise comparison for the AHP-based calculation of the subjective weights, and to convert linguistic values to numerical values for some of the criteria describing the alternatives.