Climate change is considered as one of the biggest threats that humankind is facing nowadays, with environmental, social, and economic consequences. The building sector is facing multiple climate change impacts, which is becoming more and more vulnerable. This is especially true considering that about 35% of the buildings in the European Union (EU) are over 50 years old and the replacement rate of new building in Europe is low. Therefore, it is expected that much of the existing building stock will be affected by several climate change impacts in near future. Specifically, from the building point of view, these impacts can range from a slight rise in the average environmental temperature and humidity levels to extreme and severe events (such as strong wind and floods), changing in most of the cases, the building performance, and thermal behavior. Among the adaptation strategies to climate change, the envelope optimization, whichever climate type, is the most effective way to reduce the building energy dependency and increase the indoor thermal comfort. In this regard, the integration of phase change materials (PCM) into the building envelope can produce a sort of extra thermal capacity to the building, enhancing its overall energy efficiency. Specifically, when PCM is used without any control systems, it means that it is passively contributing to the building thermal comfort, stabilizing the indoor temperature and reducing both cooling and heating demands. Considering that the effectiveness of PCM application over the building envelope is mostly associated with the selection of the appropriate melting temperature and thickness, in the context of climate change, it is expected that the optimal PCM melting point and amount found for the present period will not be optimal for future and vice versa. Therefore, the present book chapter presents a numerical investigation on the effectiveness of PCMs wall implementation as a resilient building refurbishment solution. Specifically, the book chapter aims at proofing the PCM’s capability of being an effective building refurbishment strategy, under historical and future climate conditions. The whole study is based on dynamic building simulations carried out by IDA ICE tool on a typical residential single zone house in Stockholm (Sweden) and Rome (Italy) cities. The results of the simulations highlight that PCM can contribute to a reduction of cooling demand and improve the indoor thermal comfort under both historical and future climate in Stockholm. In addition, PCM results in slight effectiveness in reducing heating loads, and the total annual energy saving is between −1.5% and −2.4% for the historical period and −1.9% and −5.7% for the future one. In Rome, the incorporation of a PCM layer in the building envelope slightly reduces the cooling demand and enhances the indoor thermal comfort, where the total annual energy saving equals to −1.6% for the historical period. Conversely, no beneficial effects in term of annual energy saving have been observed for future climate condition in Rome.