Burying ducts beneath loose-fill insulation or encapsulating ducts in closed cell spray polyurethane foam (ccSPF) can significantly reduceconductive losses and gains for unconditioned attic installations. Calculated R-values of buried and/or encapsulated ducts are needed to determinethe energy savings resulting from installations of buried ducts. Effective R-values for four duct configurations (traditional, encapsulated, buried,and both buried & encapsulated) were calculated using closed form equations and finite element methods. R-values for a 200 mm (8 in) roundflexible duct were found to range from RSI-1.5 (RUS-8.8) for code-minimum duct insulation to R_SI-8.4 (R_US-47.7) for deeply-buried ductsencapsulated in 38 mm (1.5 in) of ccSPF. Parametric simulations were performed for varying radii and loose-fill insulation heights, andgeneralized correlation equations for R-value were calculated from these simulations. While linear interpolations of tabulated values provide overallduct system R-values that are accurate to 7% of simulated values, these correlations are accurate to 0.07%. As buried and/or encapsulated ductsare accepted as a method of meeting the more stringent duct insulation requirements of new building codes, these R-value calculation methodologieswill provide needed quantification of the potential energy savings.