Blown Insulation for Existing Vented Attic Description Guide describing how to insulate a vented attic in an existing home using blown insulation added to the attic floor.
Ducts Buried in Attic Insulation Description Guide describing buried ducts in loose-fill attic insulation, a method that can only be used in dry climates.
Ducts Buried in Attic Insulation and Encapsulated Description Guide describing approaches to burying and encapsulating ducts in unconditioned attics to increase the overall R-value of duct insulation.