## 4 Application of Green Roof on the Existing Building
### Model and Parameters
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type 1—Layers** & **d [cm]** & \(\rho\) [kg/m\({}^{3}\)] & **Weight [kN/m\({}^{2}\)]** & **Weight [kN/m\({}^{2}\)]** \\ \hline concrete or stone tiles & 3–5 & 200–2400 & above concrete laid to & \\ sand (or without) & 3 & 1800 & fall layer & above roof plate \\ \hline hydro-insulation & 1–2 & 900 & q = 1.02–2.51 & q = 1.56–3.01 \\ \hline cement screw (or without) & 2–3 & 2100 & & \\ thermal insulation (or without) & 3–6 & 100 & & Whole roof structure \\ concrete laid to fall (or without) & 3–5 & 2400 & & \\ \hline roof plate structure & & & & \\ \hline
**Type 2—Layers** & **d [cm]** & \(\rho\) [kg/m\({}^{3}\)] & **Weight [kN/m\({}^{2}\)]** & **Weight [kN/m\({}^{2}\)]** \\ \hline asphalt or gravel & 2–5 & 1800–2000 & above concrete laid to & \\ hydro-insulation & 1–2 & 900 & fall layer & above roof plate \\ \hline cement screw (or without) & 2–3 & 2100 & q = 0.90–1.25 & q = 1.71–2.56 \\ \hline thermal insulation (or without) & 3–6 & 100 & & \\  & & & & Whole roof structure \\ concrete laid to fall (or without) & 3–5 & 2400 & & Typical U [W/(m\({}^{2}\)K)] \\ \hline bitumen layer (or without) & 0.5 & 900 & & \\  & & & & \\ \hline roof plate structure & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristic layers and weight of different types of flat roofs according to [17]. Figure 2: Micro location and the possible green roof implementation: (**a**) on the roof of the analyzed building; (**b**) on the entire block of buildings. The installation of a green roof in the proposed models would be performed after the removal of all non-structural elements above the last slab in the building. Consequently, the weight of the new roof structure would be reduced compared to the weight of the existing roof. The estimated mass of the proposed types (Table 2) of the green roof ranges from 125 kg/m\({}^{2}\) (EGR) to 250 kg/m\({}^{2}\) (IGR). In general, additional capacity can be introduced to account for the increase in load due to the saturation of soil and maintenance loading [59]. Regarding the uniqueness of building typology and condition, structural analysis or survey is recommended in most cases [67], especially in the potentially active seismic area, where the additional load on the roof has global implications on the whole building structure. The configuration of the model of EGR and IGR structures and its properties are shown in Table 2, where the highest values of parameter correspond to the IGR model, and the lowest to EGR model. The thickness of the layer is marked as d, density with \(\rho\), specific heat with c, and thermal conductivity with \(\lambda\). Thus, the variation in the composition of the green roof layer can give different outcomes in thermal properties and numerical models [68; 69; 70; 71], which modifies the peak cooling load and energy consumption. However, since the aim of the paper is a general approach in the profitability of the analyzed project, detailed variation of the layer properties is not performed. As presented later in the conducted sensitivity analysis, the dependence of the calculated energy cost reduction indicated the overall importance of the savings achieved by installing a green roof. Energy efficiency measures consider different levels of thermal envelope retrofitting, and the effects of those actions are usually determined relative to the current state. Results of greening the roof can additionally improve energy consumption, even after the possible usual measures of energy renovating in the buildings--the so-called business as usual (BAU) scenario. In the model of partial renovation (flat roof renovating excluded) assumed in ref. [65], the BAU scenario predicted 20% of heating energy savings, which can be compared with the energy savings in the presented analysis. On the other hand, in ref. [72], 15% of energy savings represents a low renovation scenario, and 45% of energy savings represents a moderate renovation scenario.