Lightweight structures, made with light materials or optimized designs, are a solid engineering solution for new constructions and restorations, supporting sustainability in construction. This study evaluates two case studies of complex all-FRP (Fiber Reinforced Polymer) structures, except for steel bolts, focusing on maintenance and life cycle assessment (LCA). The first case is a large strut-and-tie structure built in L'Aquila, Italy, in 2010 after the 2009 earthquake, one of the world’s largest FRP structures. It features open H-shaped beams and plate connections made via pultrusion and bag molding processes, using glass fibers and a vinylester matrix. The second case involves a pavilion initially built on the IUAV University campus in Venice, later relocated to a European refugee camp. It uses pultruded FRP beams and panels with similar materials and methods. The paper outlines maintenance procedures, torque loss in bolts, visual inspections, and structural performance under service loads, alongside reflections on LCA and design.