**5. Optimum U-value levels on the basis of a total carbon analysis**

The following section utilises the range of embodied carbon values presented above in order to identify the associated optimum U-value measures and present the uncertainties such discrepancies can cause in early stage building design decision making. **Figure 7** demonstrates these points and clearly presents the broad range of identified optimum points that can be achieved using the same type of insulation material depending on the source of embodied carbon values used.

The range of embodied carbon associated with Cellulose insulation as an example, leads the optimum U-value points to cover values from 0.15 W/m2 .K to 0.35 W/ m2 .K. This applies to all other insulation materials as well with MW and PU covering 0.16–0.25 W/m<sup>2</sup> .K and 0.21–0.29 W/m2 .K respectively.

Comparing VIP values with other insulation materials demonstrate that U-values lower than 0.21 W/m2 .K could not be reached without leading to an increase in the total carbon values. The VIP values however show comparable results with PU insulation, although due to its higher GWP values, the total carbon value is higher for identical optimum U-values. This is also investigated by Resalati et al. [1] where it was *An Aggregated Embodied and Operational Energy Approach DOI: http://dx.doi.org/10.5772/intechopen.103073*

#### **Figure 7.**

*Optimum U-value points associated with the GWP data points generated on the total carbon curve.*

observed for VIPs that their interquartile range was almost double of those for PU. The values demonstrate the CEL, EPS, GW, and MW insulation types allow for lower U-values to be reached, in the context of assumptions applied to this study. **Figure 7** further highlights the sensitivity of identifying the optimum insulation levels for low and zero energy buildings to the assumption applied to the LCA models.

The optimum insulation levels based on an aggregated operational and embodied carbon approach allows for identifying the effectiveness of building fabric design in meeting the carbon savings targets. This has been presented that an operational carbon only approach, as is required by the current building energy codes and regulations, does not necessarily lead to a lower overall energy load when compared with an aggregated approach. This has also been concluded by Mohazabieh et al. [52], Gul and Patidar [53] and Stephan et al. [15].

The analyses here further highlights these implications for subsequent future regulatory requirements, and hence provide the building product manufacturers with appropriate tools for analysing their products' place in any future market where a total carbon approach is applied to building design in principle. The key concept here is that the discussion of factoring embodied energy/carbon into building design decisions is well past the point of questioning its significance and more addressing the challenges of how best this could be incorporated into our existing regulations. This is also concluded in a study presented by Lutzkendorf [54]. Further delays in factoring in the environmental performance of various materials, products, and services when calculating/regulating the required U-values in building design can in principle lead to the design choices that increase the carbon footprint rather than reducing it.

The findings also provide meaningful insight for developing novel insulation technologies. Any new technology will need to have very low levels of embodied energy relative to its R-value if lower insulation levels are to be achieved with the embodied energy values factored in. This can either be achieved using low impact materials or with appropriate plans for end-of-life recyclability. VIPs for instance offer huge potential to be used in future low and zero energy buildings given their very thin nature relative to the thermal conductivity measures, and can potentially outperform the conventional insulation materials based on an aggregated carbon approach. Appropriate end of life treatments however, need to be considered for VIPs to be competitive in the market environmentally.
