The building provides to the occupants a shelter envelope and comfortable interior climate conditions. Starting from our ancestors, climate directly has great influence on both building design and the corresponding building’s overall energy performance. Nowadays, passive design has been getting popular again for taking advantage of the regional climate to maintain a comfort indoor climate, so as reducing or eliminating the dependence on active systems. Along with the prolonged construction service years, the current appeal of passive design is not only facing historical weather but also the changing future climate. It is undoubted that there is an ever-widening disparity between historical weather patterns and current—not to mention future—climate conditions resulting from anthropogenic changes. Consequently, this chapter focuses on this field and presents a preliminary climate-adaptive design study for urban multifamily buildings at early stage. Special attentions are paid to the indoor thermal comfort and minimum energy use from today to the last part of the twenty-first century. The generated future climate data combined with thermal comfort model assessment has been proposed as a new way of including future climate scenarios in preliminary building design for two representative sites, in Rome, Italy, and Stockholm, Sweden. The existing vulnerability to the expected climate conditions from psychometric analysis indicates that (1) the climate trend in Rome would gradually lead to more failures in the majority of conventional adaptive design measures, as the cooling and dehumidification demands would rise from 5.3% to 23.6%, while the heating and humidification demands would decrease from 27% to 16%, and (2) the climate trend in Stockholm would result in an increased comfort period by exploiting more adaptive design measures, since the heating and humidification demands would be reduced from 67% to 53%. However, the cooling and dehumidification demands would increase slightly from 0% to 1.5%. Accordingly, four main key risks are identified: (1) overheating would become a rising increasing public health threat for buildings in Rome that rely exclusively on natural ventilation; (2) open questions remain for the design team in the area of correct cooling load selection, additional space for the future installation and the effectiveness of current cooling device, etc.; (3) occasional heat waves and gradual rising humidity levels are expected to be a vulnerable topic for conventional lightweight building in Stockholm; and (4) buildings with a heavy heating load would tend to have greater cooling demand, especially those with poor ventilation resources or greater internal gains. In conclusion, it is suggested that envelope optimization, whichever climate type, is one of the most efficient and effective adaptation measures toward future climate conditions. After that, a detailed case study with a new container building is proposed accordingly.