Permanent fireproof concrete roofs which are water-tight without conventional roofing or membrane are now practical and economical in prestressed concrete. The basic theory used in designing a prestressed concrete deck for water tightness is similar to that used for many years to make prestressed concrete tanks water-tight. By compressing each element of a concrete roof slab in both directions to a net compression of about 500 psi, the concrete is made crack-free and impervious to water. It has been interesting to note that the undersides of the roof slabs have shown no evidence of water seepage through the prestressed concrete slabs, even with as much as a 6 inch head of water on the top surface of a 3 inch slab. The construction procedures used in making water tight prestressed slabs are straight forward and no special equipment is required. To obtain maximum speed and economy, prestressed concrete lift-slab construction was used for all of the parking deck structures. The control and supervision of both steel and concrete placement was much easier at ground level- also, most of the shrinkage and elastic shortening of the slabs took place before the final connections were made to the columns and walls. Ready mixed concrete was used on all of the jobs. Special care was taken in designing the concrete mix so as to hold the shrinkage to the minimum. This was accomplished by using a large quantity of maximum size aggregate and holding the cement factor to the minimum. The concrete was placed with between 3 and 4 inches slump and the specified 28 day strength was 4000 psi. The specifications allowed the stressing of the post-tensioned tendons at a concrete strength of 3500 psi- this strength was in almost all cases achieved in seven to ten days.