Sealants used in weatherseal applications are subject to both environmental and mechanical aging during their service life. Environmental aging consists of interaction with sunlight, rain, or moisture, and other atmospheric agents such as ozone. Mechanical aging is linked to the expansion and contraction of the different substrates (glass, concrete…) due to temperature variations. In order to assess the durability of sealants, the ISO 11600 norm includes separate tests for movement capability (ISO 9047) and UV irradiation (ISO 11431) but no combinations of those tests. In 1991, the RILEM TC139-DBS “Durability of Building Sealants” was created to develop new and more adapted testing. The testing proposed by this comity, was a combination of accelerated weathering (humidity and UV) combined with thermo-mechanical cycling. This study compares the durability of silicone sealants and newly developed Si-modified organic based sealants using alternated cycles of ISO 11431 and ISO 9047 during a one year period. Results show that most Si-modified organic will show limited durability in weatherseal applications mostly because of poor UV resistance. Newly developed Si-organic based sealants tested during this work show excellent UV resistance but poor elastic recovery after compression at high temperature (70 °C). This poor elastic recovery limits their long term movement capability. However, good durability can be expected with designs leading to lower movement capability than those obtained from the ISO 11600 testing.