Below Deck Spray Foam Insulation for Existing Roofs Description Guide describing how to add spray foam insulation to the underside of the existing roof deck as part of the conversion of a vented attic to an unvented, insulated attic.
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.