Modular free-form roof envelopes: watertightness restoration and durability testing of silicone-sealed joints

This paper addresses the refurbishment of a modular free-form envelope composed of glazed and opaque panels with silicone-sealed joints. The case study is a 4,500 m² envelope with complex 3D geometry, formed by more than 2,200 triangular and quadrangular double-glazed or aluminium sandwich panels. The watertightness along panels was originally provided by silicone sealing beads, which over time failed to ensure adequate durability due to joint design, installation deficiencies, and the absence of maintenance. Ageing phenomena led to widespread seepage, while temporary measures, such as the application of butyl tape over all joints, proved ineffective in the long term. Two alternative refurbishment strategies were evaluated: the replacement of glazed panels with stepped glasses to eliminate through-bolts for pressure plates, and a more conservative approach involving the renewal of joints with newly designed double-layer silicone sealing beads. The latter was selected for its lower cost and reduced invasiveness. To assess the long-term durability of the selected silicone sealant, specimens replicating the actual geometry of the envelope were subjected to an accelerated ageing programme in a weathering chamber simulating twenty years of real-world exposure. Conditioned samples were then subjected to mechanical tests under tensile–shear and bending loads to evaluate mechanical performance of the material and reproduce expected displacement. The experimental campaign confirmed the capability of the material to withstand expected conditions. Prior to large-scale installation, full-scale on-site sampling was carried out in representative areas of the envelope. This phase allowed for the refinement of installation procedures, identification of logistical and geometric constraints, and optimisation of working conditions to ensure both safety and curing quality. The paper presents the design, laboratory testing, and field validation process, highlighting their combined role in developing durable refurbishment strategies for complex building envelopes.