A 12 sided double curved conoid shell roof, 3 inches thick with a clear unsupported span of 66 feet, has been built without formwork for the Beth Israel Synagogue at Miami Beach, Florida. The structure was designed fro hurricane load conditions. Construction of the roof and sides of the building was accomplished with gas concrete sprayed at low pressure on a fabric of metal riblath hooked to reinforcing rods. The shape of the roof was first created by erecting a temporary tower in the center, elevated above the edge beam, and draping reinforcing bars radially from the center ring (apex) to points at the rim. The prefoamed concrete was then applied in layers to a uniform thickness of 3 inches. The final layer on the top was extra dense to provide moisture resistance, and the final coat underneath was finished to provide good acoustical properties. After the concrete had reached the desired strength, the center tower is removed, and the ‘catenary' reinforcement relaxes and goes into compression as does the gas concrete. The final shape is, thus, a corrugated conoid, supported on columns, and completely in compression. The horizontal thrust at the rim is taken by the steel beam which forms a ‘tension ring' around the perimeter.