The new mellon national band and trust company in suburban Pittsburgh has an elliptical-shaped roof featuring arched overhanging vaults integrally joined with a central compression and tension ring and supported by 22 outside columns so that the ceiling is the same shape as the exposed roof. The vaulting is highlighted by special, concealed lightening to give visitors the impression that the roof is open to the sky. A glass-domed 12 foot diameter skylight tops the compression ring. The roof design is said to be an "architectural first." The ceiling is formed by 22 vaulted concrete shells, 11 identical pairs, with each pair varying in length because of the elliptical design. The shells are as long as 35 feet, including a 4 foot overhang around the periphery of the building. There each vault is 11 feet wide and 7 feet high. This decreases gradually as the vault reaches the compression ring, where it is 1 and one-half feet wide and 2 feet high. Since conventional rigid insulating materials were not adaptable to the contours of the roof, a thermal insulating polyurethane foam was sprayed over three-eights of an inch metal rods, metal lath and cement plaster. It was covered with reinforcing rods and 5 to 9 inches of concrete. The foam material has a compression strength of 38 pounds per square inch, sufficient to prevent appreciable compression from the concrete. The foam is expected to reduce building heating requirements because cold from the roof exterior will not reach the ceiling and necessitate additional warm air to offset it.