Silicone sealants have been used since the 1960s as an adhesive to bond glass/glass and glass/metal constructions in facades and buildings, and a unique assembly type evolved around this time that came to be known as structural silicone glazing (SSG). In these systems the silicone sealant acts both as an elastomeric adhesive transferring applied glazing loads to supportive metal framing as well as a seal maintaining air and watertightness. Such systems offer numerous benefits as well as the opportunity of creating walls of uninterrupted glass and other unique aesthetic features without visual mechanical attachment of glazed elements. In general, the past 45 years have shown that the silicone sealants previously and currently employed have remained durable enough to maintain a healthy service life, but what is the actual service life of these systems? Because there is a life-safety aspect to SSG, a commonly asked question that demands continual study but remains elusive pertains to predicted longevity. Simply put: “How long can SSG systems last before replacement becomes necessary?” This paper provides information gleaned from numerous existing SSG installations from the 1970s and 1980s via field visits, extraction of structural silicone sealants, and subsequent laboratory evaluation of aged silicone rubber. Data were obtained through glass replacement works or from investigative inspection.