Buildings are one of the United States's largest consumers of energy. Measures to decrease energy consumption often are overlooked during the building design process. One of the major barriers in design of buildings is the absence of tools to help architects and designers during the preliminary design stages. Therefore, the objective of this study is to develop an estimating tool to assess the energy performance and economic benefits of radiant barrier insulation in the temperate climate region in the United States. The developed tool is based on transient 3D finite element models that were validated based on the results of an experimental field study. The results of the 3D finite element models were used to develop a set of multiple-linear regression equations to predict the thermal and energy performances of radiant barrier insulation. The simulations run hour by hour for the entire year using the typical meteorological year (TMY2) weather data. Each simulation takes less than 30 seconds, allowing for very fast comparisons of different design scenarios. It is expected that the developed tool will simplify the integration of energy efficiency in residential building design and construction. Results show that attic radiant barrier can reduce building energy consumption by up to 12%. Results also indicate that cost savings in the temperate region ranges from $7 in Idaho to $41 in Connecticut in 2011.