Quantifying the benefits of radiant barriers is complex because the benefits depend upon the climate, attic geometry, duct arrangements, and other building parameters. Homeowners, however, require simplified guidance regarding building envelope options, even those options that seem to have no simple answers. An extensive parametric evaluation of radiant barrier installation alternatives was made using a newly expanded and benchmarked version of an attic simulation program. To complement this analysis, a detailed numerical analysis of radiation heat transfer within the attic and within the small space bounded by the rafters and the sheathing was completed. The results provide guidance for homeowners and builders.