## 5 Conclusions  
Passive construction is expected to increase due to European environmental regulations and the sensibility of police makers related to building energy consumption. For this reason, the use of NDT as a diagnosis tool could be essential to verify the compliance with design technical specifications. Along this line, the main contribution of this research is the analysis of the applicability of non-destructive techniques for the post-construction evaluation of thermal transmittance of passive house facades in steady-state conditions.  
According to the literature review, the heat flux meter method is a non-destructive technique standardized by ISO 9869-1:2014 [76]. Currently its use in PH is not very widespread, even in the Mediterranean climate. Indeed, the literature review showed that some constraints of applying the _HFM_ average method can arise when the practitioner wants to verify the compliance with technical specifications of projects in facades with low U-value. One of the main constraints is the high deviations obtained between the measured and its corresponding theoretical U-value, as can be seen in previous studies. According to [PERSON] et al. [23] and [PERSON] et al. [28], these deviations are more pronounced when climatic conditions are not stable during the monitoring process. Another constraint is the fact that some testing parameters for the monitoring process are not fully specified for measuring facades with low U-value by the Standard ISO 9869-1:2014 [76], such as temperature difference between indoor and outdoor environment and the test duration. Concerning the quantitative _IRT_, a significant reduction of the prices of IR cameras [33] led the researchers to put their efforts in the development of accurate approaches related to the thermal characterization of building envelopes. Nevertheless, a gap still exists in the implementation of _QIRT_ in passive houses.  
In the current research, the assessment of an experimental mock-up with controlled climatic conditions allowed to check the possible suitability of the NDT in highly insulated walls and to define good practices for a detached house based on PH concept under real environmental conditions. Based on the analysis of results and the respective discussion, this study demonstrated that the _HFM_ average method and quantitative internal _IRT_ can be executed successfully for determining the in situ U-value of passive house facades. Despite this, neither one of the NDTs was implemented in warmer climates or conducted in summer. Hence, the applicability of the _HFM_ average method and the quantitative internal thermography has not been demonstrated under these mentioned boundary conditions, and, consequently, further research is needed. Furthermore, the practitioner should choose the method, depending on test duration, thermal gradient, experience in measurement campaigns, and knowledge in data analysis.  
Conceptualization, K.G. and B.T.; methodology, K.G. and B.T.; software, B.T.; validation, K.G. and B.T.; formal analysis, K.G. and B.T.; investigation, K.G. and B.T.; resources, M.C.; data curation, M.C.; writing--original draft preparation, K.G. and B.T.; writing--review and editing, M.G.; visualization, M.G.; supervision, M.C.; project administration, M.C; funding acquisition, M.C. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by the Government of Catalonia, Research Grant 2017-SGR-227.  
The authors acknowledge Eovwall Technology for providing the experimental mock-up and the detached house and facilitating the monitoring process.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.