This paper explored the temporary facilities created during the pandemic for use as COVID-19 test centers at Zaventem Airport, the main airport for the city of Brussels, Belgium. The possibilities of modular construction technology and the impact of the building envelope on users’ perception of indoor space comfort and privacy were closely observed. The three main problem statements were as follows: (1) the COVID-19 crisis indirectly influenced the creation of temporary modular buildings with glass envelopes; (2) the modular envelope is adaptable to the existing context; and (3) the envelope meets the needs of the users. This study’s objectives were to identify the critical factors for users’ well-being in temporary modular buildings, and to conduct factor comparisons among different users and between different building-enclosure systems. The study data were collected through a subjective assessment using a SWOT analysis and a survey questionnaire. The glass facade affected the users’ acceptance levels of comfort and privacy. The main results show that the users were satisfied with the level of comfort and dissatisfied with the level of privacy. This information can be used to identify areas for improvement and provide useful feedback to designers and engineers about specific design features and operating strategies for temporary modular emergency healthcare buildings.