Unique application of the catenary suspension concept has been used for the 136 foot clear span, lightweight concrete roof deck of a new supermarket in San Francisco. The catenary principle so frequently used in suspension bridges, is the most economical structures known. The form in this supermarket application takes a natural catenary shape to a predetermine sag governed by the designed rigidity of the roof. The supermarket roof covers 16,000 square feet. The slab of vermiculite concrete was placed on paper backed wire lath and attached to 3 /8 inch high tensile stranded wire. The vermiculite concrete provided a lightweight, fireproof roof slab with high insulating qualities. The concrete was then pumped through a hose to the roof. On the under side, 2 inch by 2 inch by 16 gauge welded wire fabric was wire-tired to the floor lath, and vermiculite-gypsum plaster was manually applied in two coats to a thickness of 3 /4 inch.