Ducts located in an attic or crawlspaces are generally considered accessible because code requires access to those spaces. Access is usually gained by opening a door, hatch, or other moveable panel. If this can be done without causing damage that would need to be repaired, this is considered accessible. Somewhat counter intuitive is that ducts buried under insulation in an attic may be considered inaccessible. Essentially the benefit of pulling the ducts out of the insulation to reduce duct leakage is outweighed by the benefit of leaving them buried to reduce losses due to conduction of heat.