A saving of one-half million dollars in construction costs is claimed for a 34 story office tower which is located over the intersection of two main subway lines in Toronto. Key factors in the savings were the use of: structural lightweight concrete which reduced dead loads and prestressed flat-plate floors which reduced the total height of the building. Because of these two factors it was possible to reduce the size of the prestressed foundation girders on which the building is carried. The girders were stage-post-tensioned, a relatively new technique that also saved money. Cost advantages with structural lightweight concrete increase in proportion to the height of the structure and length of spans. Reduction of dead weight in this 34 story tower saved money by permitting smaller columns and minimum-depth foundations. To construct the post-tensioned lightweight concrete floors the contractor erected flat-soffit flying forms for the entire floor area and installed welded-wire fabric in the bottom of the forms. After the lightweight concrete had developed a compressive strength of 3000 psi, hydraulic post-tensioning jacks were placed on the exterior edges of the slab and pressure was applied against anchors embedded in the hardened concrete to stress the tendons. These tendons were then held by end anchors in which the strand is permanently attached and left unbonded. Grouting was entirely eliminated, thus saving considerable time and money.