This paper presents a parametric study of the effects that shingle absorptivity, radiant barrier emissivity, attic ventilation flowrate, and roof slope have on the performance of radiant barriers in symmetrical residential attics. A heat balance model was developed to investigate these effects. The model was validated against experimental data and was found to predict with good accuracy. Of the four parameters investigated, only emissivity of the radiant barriers had first-order effects on their performance. Variations in the performance of the horizontal radiant barrier (HRB) configuration were minimal in the other three parameters. The truss radiant barrier (TRB) configuration showed slightly more variations because of the presence of uncovered end-gables. This paper presents a brief description of the heat balance model, the parametric studies and conclusions.