**5. Conclusions**

This chapter reviews the life cycle assessment method, its stages, and methods for impact assessment. Many LCA variants have been proposed to include other aspects of sustainability, that is, social (SLCA) and economic (life cycle costs), rather than only accounting for environmental impacts. Although many improvements have been proposed to the original LCA method version, the flexibility associated with framing the LCA boundaries according to the designer's willingness stands out to assess the product's impacts over its life cycle. This flexibility makes it difficult to push new design paradigms to achieve true sustainability in context. The biomimetic design approach follows such a design paradigm since it looks for natural inspiration but limits its focus to solving human problems.

On the other hand, biomimicry design approaches go further toward strictly achieving sustainability under the binary orientation. This before led us to ask whether biomimicry can help improve the current LCA method's way of evaluating impacts, following the "nature success" philosophy. The literature analysis suggests that most impact assessment tools today still struggle to evaluate from the point of view of "achieving sustainability" instead of "reducing unsustainability." Among the tools found, three potential tools based on biomimicry principles are analyzed. Only two provide detailed quantitative criteria but only for the environmental aspect and following the constituents of "assess to conditions of sustainability." However, although these two tools greatly advance the current frameworks to evaluate impacts for biomimetic-based and cradle-to-cradle-based designs, they still present limitations on "assessing achievement" since their criteria reflects the assessment of progress improvement. Conversely, the Biocircular model approach offers great potential to frame the "achieving sustainability" paradigm since it still is in the early stages of development.

Moreover, two case studies were analyzed under the constituents of "achieving sustainability" and "assessing progress": (i) a net zero energy building by comparing a new design with a design to retrofit, and (ii) a sustainable construction project. Both cases are analyzed under the usage phase of the life cycle.

Finally, the present work, by presenting the analysis of current LCIA tools from the point of view of the "achieving sustainability" paradigm, hopes to bring the attention of designers and engineers, especially to the construction sector. Urgency is required due to a rapid shortage of resources and a deliberate (or unintentional) increase in waste production.
