Triangular elements for forming geodesic structures each have three elongated leg members arranged end-to-end to form three apexes. At least one of the apexes is formed with a curved-shaped indentation which extends along an outer surface and perpendicular to the opposing side surfaces. The legs of each triangular element also include one or more outer grooves extending longitudinally along the outer surface. Each outer groove is sized to receive a seal member. An inwardly raised shoulder extends longitudinally along the inner surface. An inner groove is formed along a side edge of the raised shoulder and each inner groove is sized to receive a seal member. Panels are positioned over the opposing sides to form double-walled triangular element. Channels extend through the outer surface and raised shoulder of the inner surface. The triangular elements are arranged to form a geodesic structure and fasteners extend through the channels to secure adjacent triangular elements.