The report is a revised version of a support document for the performance testing portion of the proposed Florida statewide building standard for radon-resistant construction. The support document was developed by the Alternate Performance Standard Development Committee of the Florida Radon Research Program (FRRP), commissioned by the Florida Department of Community Affairs. The report contains the rationale and technical justification for the version of the Performance Testing Section (Section 5) of the standard which was recommended by the Standard Development Committee, as well as recommended text for the section. The recommendations and draft standard language were based largely on an FRRP research project which involved study of short- and long-term average indoor radon concentrations in 80 Florida houses for over a year. At the time of the committee report the project had collected 6 months of data from about ha lf the houses and 3 months of data from the remaining half. After a brief review of the variability of indoor radon, the report describes background, methodology, data analysis strategy, and early results from the short-/long-term radon correlation project. These are followed by a rationale for the recommended standard section.