# Retrofitting a Building's Envelope: Sustainability Performance of ETICS with ICB or EPS
## 5 Results
### Comparative 3E Performance of ETICS with ICB and Expanded Polystyrene (EPS)
#### 5.2.3 Comparison of the Economic Costs and Benefits of ETICS with ICB or EPS  
The results achieved in the comparison of the economic balance concerning the NPV of the C2C cost of the external wall alternatives (Figure 9) show that the use of EPS in ETICS provides a saving in the acquisition costs at stages A1-A3, A4 and A5 varying from 28% to 30%. When analysing the NPV of the C2C cost, this value is reduced due to the significance of the maintenance and energy costs, but it still reveals an economic advantage of using EPS in ETICS due to its lower market cost when compared with ICB.  
With the results from Figure 9, it is also possible to conclude that none of the wall alternatives where ETICS with ICB or with EPS were applied provide any \"economic savings\" in comparison to the reference solutions. However, the results shown were obtained considering a consumption of energy corresponding only to 10% of the needs for heating and cooling during the B6 substage. If higher values (35% and 50%) are used to simulate future expectable scenarios for dwellings or multi-familiar residential buildings, these \"economic savings\" become more significant. In fact, Figure 10 demonstrates that the alternatives with 9 cm of ICB in ETICS have a better performance than the reference walls from an energy consumption point of view to fulfil 35% (W7 in the single-leaf wall group) or 50% (W14 in the cavity wall group) of the heating and cooling needs. For a consumption value of 25%, the alternative of ETICS with 9 cm of EPS (WE7) becomes the best alternative in the single-leaf wall group. In the cavity wall group the WE14 solution (also with 9 cm of EPS) becomes the best alternative only for a consumption pattern of 35%. Nevertheless, the alternatives with ICB in ETICS always present a higher NPV of the C2C cost than the ones with EPS independently of the consumption pattern that is considered for the use stage, because of the higher acquisition cost and U-value for the same thickness of insulation.  
Figure 9: NPV/m\({}^{2}\) of external wall of the economic (A1–A5, B2–B4 and C2–C4 and D stages) and energy (B6 stage) costs of ETICS with ICB and EPS.  
Figure 11 is similar to Figure 10, but only includes the external wall alternatives that were renovated by the application of ETICS and also indicates their corresponding U-values. This chart helps the decision-maker to choose the best energy renovation alternative from a C2C economic point of view depending on the U-value and consumption of energy wanted and on the available budget.  
Figure 11: Difference between the NPV of the economic (A1–A5, B2–B4 and C2–C4 and D stages) and energy (B6 substage) costs of each external wall alternative renovated and the NPV of W1, considering different consumption patterns for the use stage (guaranteeing 10%, 25% or 35% or 50% of the energy needs) and considering the corresponding U-values.  
Figure 10: Difference between the NPV/m\({}^{2}\) of external wall of the economic (A1–A5, B2–B4 and C2–C4 and D stages) and energy (B6 sub-stage) costs of each external wall alternative and the NPV/m\({}^{2}\) of W1, considering different consumption patterns for the use stage (guaranteeing 10%, 25%, 35% or 50% of the energy needs) of ETICS with ICB and EPS.