## 5 Results and Discussion  
EnergyPlus 9.1.0 software with the EcoRood model [76] was used for the computation of the heating and cooling energy needs. Different outcomes for the reduction in the building's annual energy need for cooling and heating (for the last floor) are demonstrated in Table 5 and Figure 3. As a result of the currently insufficient thermal insulation, the analyzed apartment can potentially reduce the consumption up to 22% of heating and 21% of cooling energy with the implementation of IGR compared to the current state (Figure 3b), which is in the range of savings obtained in BAU scenario measures. On the other hand, IGR models reduce the need for cooling energy significantly more than the proposed EGR model. In the corresponding economic analysis, the yearly benefits of heating and cooling energy reductions, for models with EGR and  
The results of the economic analysis are presented in Table 5. Based on the presented input data for the apartment under the green roof, the life cycle NPV for model 3 is computed in the range of EUR 17/m\({}^{2}\) to EUR 132/m\({}^{2}\), depending on the type of the roof when the property value increase is accounted as a benefit. By analyzing the models without this benefit, it can be said that there are dominantly negative outcomes of NPV values for scenarios 1 and 2, which may be the case with similar location and envelope properties. It is important to emphasize that the analyzed object has eight residential units, and for similar energy performance buildings with a higher number of RU, individual users (investors) could have lower installation costs but lower benefits from membrane longevity as well. Therefore, sensitivity analysis evaluated the impact of this parameter. Since the social benefits, but also the costs, are excluded from the NPV model in this paper, corresponding life cycle assessment analysis should incorporate the negative aspects of old roof disposal aspects as well. Since the uniform variations included an estimated green roof lifespan of 40 to 55 years, in Figure 4, the most probable result for NPV of the life cycle projected to 47 years is presented for all models. These results indicate that energy savings are not the crucial aspect of the economic benefits of investment, even for the model with the IGR. Based on the calculation, it is clear that the payback period is not more than one year for the models incorporating this benefit. This outcome is expected because the increase of the property value has become significantly higher than the initial costs--if it is distributed on all residential units of the building. An analogous observation is in accordance with sensitivity analysis. Moreover, the property value increase broadly determines the outcome of the NPV at the end of the life cycle, and the shape of the LCC curve is depicting the asymptotic tendency of the final result (Figure 4.). The influence of a number of residential units is analyzed through sensitivity analysis. For the different numbers of RU, the NPV value curve tends to increase or decrease with a high rate for all models, which will be indicated in the sensitivity analysis. For an individual investor (number of RU = 1) in the equivalent model, the NPV value would further decrease to EUR -176/m\({}^{2}\), EUR -254/m\({}^{2}\), EUR -124/m\({}^{2}\), and EUR -170/m\({}^{2}\), for models 1 EGR, 1 IGR, 3 EGR, and 3 IGR, respectively. LCC analysis can present different results depending on the climate and economic parameters, but various costs and benefits that are included in the calculation could alter the results as well. In ref. [14], the most probable NPV for installation of EGR on detached house was calculated as USD 351/m\({}^{2}\), with significant benefits obtained by thermal envelope improvement. In the first scenario in ref. [55], where property with a constructed green roof is being used after construction, the most probable NPV is calculated as USD 173/m\({}^{2}\) and USD 213/m\({}^{2}\) for EGR and IGR, respectively.