«2- , A total of 33 structures were examined. These were in various ptages of construction that varied from floor slab only to essentially complete and occupied (by the contractor supervisor). of the structures are shown in Figure l. The locations Figure 2 is a sketch of a completed dwelling. A typical building layout is indicated in Figure 3, showing the points at which measurements were made: on the center line of each wall, 10 feet out from the wall, 3 feet above the surface of the ground; in the center of the building, at a height of 3 feet; and in the center of the building, on the floor. FINDINGS Raw Data The exposure rates measured are indicated in Table 1, in micro roentgens per hour (uR/h). External exposure rates ranged from 7 uR/hr A to 55 pR/hr, with an arithmetic mean value of 20 uR/hr. Treated Data and Results Exposure rate reduction factors (RF) were computed for each dwelling except for seven "slab only" sites where no external measurements were made. The reduction factor (RF) is expressed in percent and was de- termined utilizing the following equation: RF = (1 - Interior Exposure Rate) x 100 Exterior Exposure Rate